[advances in food and nutrition research] advances in food and nutrition research volume 67 volume...

CHAPTER TWO

Implications of Light Energyon Food Quality and PackagingSelectionSusan E. Duncan1, Hao-Hsun ChangDepartment of Food Science and Technology, Virginia Polytechnic Institute and State University, Blacksburg,Virginia, USA1Corresponding author: e-mail address: [email protected]

Contents

1.

AdvISShttp

Introduction

ances in Food and Nutrition Research, Volume 67 # 2012 Elsevier Inc.N 1043-4526 All rights reserved.://dx.doi.org/10.1016/B978-0-12-394598-3.00002-2

26
2. The Chemistry of Light Energy on Foods 28
2.1
Light as a source of chemical energy 28 2.2 Food photosensitizers: Transfer of light energy to foods 29 2.3 Transition of energy in foods 31
3.
The Effect of Light-Induced Oxidation on Food Quality 32 4. Effect of Light Energy on Susceptible Food Molecules 33
4.1
Lipids 34 4.2 Proteins 36 4.3 Vitamins 36 4.4 Chlorophyll 43
5.
Effect of Selected Light Wavelengths on Light-Responsive Food Moleculesand Food Quality 44 5.1 Carotenoids 45 5.2 Flavonoids 47 5.3 Ascorbic acid 49 5.4 Riboflavin 50 5.5 Chlorophyll 52 5.6 Myoglobin 52 5.7 Food colorants 53 5.8 Protein 55 5.9 Tocopherol and retinoic acid 56 5.10 Nitrogen-containing compounds 57
6.
Food Packaging to Protect Food Quality by Interference with Light Energy 59 7. Conclusions 61 References 62
25

http://dx.doi.org/10.1016/B978-0-12-394598-3.00002-2

26 Susan E. Duncan and Hao-Hsun Chang

Abstract

Light energy in the ultraviolet and visible light regions plays a critical role in overall foodquality, leading to various degradation and oxidation reactions. Food degradation andoxidation result in the destruction of nutrients and bioactive compounds, the formationof off odors and flavors, the loss of food color, and the formation of toxic substances.Food compounds are sensitive to various light wavelengths. Understanding the effectthat specific light wavelengths have on food compounds will allow the development ofnovel food packaging materials that block the most damaging light wavelengths tophotostability of specific food compounds. Future research should focus more specif-ically on the effect of specific light wavelengths on the quality of specific food products,as there is limited published information on this particular topic. This information alsocan be directly related to the selection of food packaging materials to retain both highquality and visual clarity of food products exposed to light.

1. INTRODUCTION

Numerous compounds that occur naturally or are added as ingredients

to food products are sensitive to light energy, leading to photodegradation

and oxidation reactions. Absorption of light energy by food compounds

leads to loss of functionality of these compounds in food products. Colored

pigments can be degraded under light exposure and cause food discoloration.

Secondary volatile compounds responsible for off odors and flavors of foods

are derived from photodegradation or oxidation of food compounds

(Ullrich & Grosch, 1988). The formation of toxic compounds may occur

during light-induced oxidation, and these toxic compounds could act as car-

cinogens (Min & Boff, 2002a, 2002b). Essential nutrients in foods also can be

lost under light exposure due to photodegradation or oxidation (Sattar,

John, & Furia, 1975). The effect of light on other bioactive compounds

in functional foods is not well studied but is of increasing importance as

the functional foods market expands (Betoret, Betoret, Vidal, & Fito,

2011; Kaur & Das, 2011; Siro, Kapolna, Kapolna, & Lugasi, 2008).

Many naturally occurring bioactive compounds play roles in reducing

the risk of numerous diseases and may have potential health benefits

(Boddy, 2011). Food products fortified with bioactive compounds are

becoming increasingly popular, providing opportunities for diverse product

selection to address health and well-being of consumers. However,

photodegradation or oxidation of bioactive compounds present in food

products can cause the loss of nutritional and health benefits of some

bioactive food components.

27Implications of Light Energy

Undesirable changes in visual effects (color), which are readily evident,

are not accepted by consumers and are used as indicators of lower quality or

unsafe products. The combined effects from the loss of nutrients and bioac-

tive components with degradation of quality (color and flavor) negatively

impact overall food quality and consumer acceptance, leading to loss of

product sales, decreased trust in brand, and an economic loss for the food

industry. Packaging selection for functional foods containing natural or

fortified light-sensitive bioactive compounds is needed to provide adequate

protection.

Food packaging is a practical approach to protect foods from light dam-

age. However, consumers prefer to “see” the products in order to evaluate

quality, so many food products are packaged in clear containers (Doyle,

2004). Clear or translucent packaging, however, allows product exposure

to light wavelengths from overhead and display illumination in retail stores,

increasing the risk of light-induced degradation or oxidation (Duncan &

Webster, 2009). Numerous studies have focused on the effect of light energy

on the stability and quality of various food products. The effect of light

energy on photodegradation or oxidation of various compounds present

in foods has also been well discussed, including detailed mechanisms. How-

ever, there is limited published information associated with the effect of spe-

cific light wavelengths on photostability of food compounds. With such

knowledge, it is possible to develop novel packaging designed to protect

valuable nutritional and functional food components as well as overall food

quality (Webster, Duncan, Marcy, & O’Keefe, 2009). Packaging materials

can be designed to block specific light wavelengths that are most damaging

to photostability of specific food compounds (Webster, Duncan, Marcy, &

O’Keefe, 2011). Thus, food products can be protected from light damage

and still be visible to consumers by using designed packaging materials that

block the most harmful light wavelengths to food products.

Food packaging and food manufacturers are eager to understand the

relationship of light wavelengths to the quality of specific food products,

and how packaging materials can be designed to block detrimental light

wavelengths while still retaining product visibility. This review illustrates

the impact of light as a source of chemical energy on food quality and

reactions or mechanisms of photodegradation or oxidation of food com-

pounds under light exposure. We also review the effect of specific light

wavelengths on food quality by investigating the most detrimental light

wavelengths to photostability of food compounds. We then discuss the

selection of food packaging based on the information gathered from the

Table 2.1 Definition of terms used in this review paperTerms Definition

Quantum The minimum amount of physical quantity involved in a

reaction

Photon A single quantum of light as the basic constituent of

electromagnetic radiation

Electromagnetic

radiation

A form of energy absorbed and emitted by particles, quantum,

or photon and exhibits wave-light behavior

Electromagnetic

spectrum

The distribution of colors in the range of all possible

frequencies and wavelengths of electromagnetic radiation

Fluorescence The emission of light by a substance that absorbs energy and

jumps to a higher energy state

Incandescence The emission of light from a hot body as a temperature effect

Chromophore The functional group absorbs a characteristic UV or visible

light wavelengths

Photosensitizer A light-absorbing substance that initiates a photochemical

reaction

Singlet state A state of an atom in which all electrons have paired spins

Triplet state A state of an atom in which electrons with spins parallel to each

other

Radical Molecules with unpaired electrons

Omega-3 Compounds have a double bond three carbon atoms away

from the end of carbon chain

Photosynthesis A chemical process that converts carbon dioxide into organic

compounds using the energy from sunlight


effect of light energy on overall food quality. Table 2.1 provides definitions

of some key terms used in this chapter in order to facilitate understanding.

2. THE CHEMISTRY OF LIGHT ENERGY ON FOODS

2.1. Light as a source of chemical energy
Light is more generally referred to as electromagnetic radiation, which is the
energy that is dissipated when converted to other types of energy. The

energy of a photon is proportional to the frequency and wavelength of

the wave. Higher frequencies have shorter wavelengths, while lower

200 250 300 350 400 450 500 550 600 650 700 750 800 nm

InfraredVisibleX-ray UVC UVB UVA

Vio

let

Blu

e

Cya

n

Gre

en

Yello

wO

rang

e

Red

Figure 2.1 Wavelengths of the electromagnetic spectrum (Duncan and Hannah, 2012).


frequencies have higher wavelengths of a wave. As a result, electromagnetic

radiation is classified according to frequencies or wavelengths of its wave and

expressed as electromagnetic spectrum. A spectrum refers to light intensity

as a function of frequencies or wavelengths, as derived from the

Planck–Einstein equation (Ireson, 2000). A spectrum is divided in order

of increasing wavelengths or decreasing frequencies, including gamma rays,

X-rays, ultraviolet (UV) (200–400 nm), visible (400–800 nm), near infrared,

microwave, and radio waves (Fig. 2.1). The mechanisms of energy absorbed

by these subcategories of the spectrum differ. However, the fundamental

process is that a certain amount of energy is absorbed by each subcategory.

The UV and visible spectra are of interest for this review. The visible

spectrum (400–800 nm) is the region detected by the human eye, with dif-

ferent regions associated with different colors within the spectrum. The

seven colors associated with narrow bandwidths of light wavelength include

violet (400–450 nm), blue (450–475 nm), cyan (475–495 nm), green

(495–570 nm), yellow (570–590 nm), orange (590–620 nm), and red

(620–800 nm).

Food products may be exposed to various light sources with different

light wavelengths. The electromagnetic radiation given off by the sun is

primarily, within the infrared, UV, and visible light spectra (Erez, 1977).

A fluorescent light produces UV and visible light wavelengths through fluo-

rescence (Welch et al., 1997). Incandescence usually refers to a spectrum

region of visible light. Different light sources generate various light wave-

lengths and frequencies, affecting the response of photosensitive food

components.

2.2. Food photosensitizers: Transfer of light energy to foodsThe effect of light energy on food quality begins with the absorption of light

energy by a photosensitive compound (chromophore) in food products

(Gust, Moore, & Moore, 2001). The absorption of a photon of light by a

chromophore in food results in the transition of energy level from the “low-

est ground state” to “higher excited state,” meaning energy is transferred

from light to foods (Voityuk, Michel-Beyerle, & Rosch, 1998). The


“excited state” chromophore may lose its energy and return back to ground

state if it does not absorb another photon from light, or it may jump to

another higher energy level by absorbing more photons (Buruiana,

Buruiana, Strat, & Strat, 2004). The absorption of light energy by food com-

ponents can only occur when a chromophore absorbs those specific light

wavelengths with the precise amount of energy capable of elevating the

chromophore from a lower to a higher energy level within molecular

orbitals. For example, double bonds and conjugated diene, triene, and tet-

raene are reactive sites within chromophores and absorb UV light energy

at wavelengths 210, 233, 268, and 315 nm, with resulting excitation of the

molecule and transition from lower energy ground state to the higher energy

excited state (Ohkawa, Ohishi, & Yagi, 1978). Overall, only a small number

of compounds present in food products are already known to absorb light

energy from specific light wavelengths. As a result, food scientists are inter-

ested in investigating the effect of specific wavelengths of UV and visible light

on specific food compounds to understand the overall effect on food quality.

The energy transferred from light to the chromophore in food is tran-

sient. As the energy is transferred, the chromophore returns to the ground

state. The energy, however, may be released in the form of heat (emission),

reacting chemically with other components in foods, such as fatty acids, to

initiate autooxidation (Logani & Davies, 1980). Alternatively, the energy

can be transferred to other photosensitizers (Raviv, Pollard, Bruggemann,

Pastan, & Gottesman, 1990).

Numerous food components have been identified as photosensitizers,

including chlorophyll, myoglobin, and riboflavin (Foote & Denny, 1968).

A common feature in the chemical structure of these compounds is the pres-

ence of conjugated double bonds (Fig. 2.2) which are sensitive to photon

excitation, especially in the regions of UV and visible light (Iwata, Hagiwara,

& Matsuzawa, 1985). The excited singlet photosensitizer (1Sen*) is

generated from the ground state of singlet photosensitizer (1Sen) under light

illumination. A photosensitizer in its singlet state absorbs light energy in

picoseconds and becomes excited for a short period of time (<10 ns)

(Choe &Min, 2006). During this brief excitation, the singlet photosensitizer

reacts by either decaying back to the ground state, generating fluorescence or

heat as it loses energy, or forming another excited triplet photosensitizer

(3Sen*) through intrasystem crossing (ISC) (Choe & Min, 2005). Excited

triplet photosensitizer (3Sen*) has a much longer lifetime compared to that

of excited singlet photosensitizer (1Sen*) and can proceed in either type I or

II pathways (Takemura, Ohta, Nakajima, & Sakata, 1989).

Riboflavin

Chlorophyll a

Myoglobin

N

N N

O

NH

O

OH

OH

H

N N

Fe

NN

HCCH

COOHHOOC

OH

N

N

N

O

OOCH3O

2O

N

Mg

OH

C

HC

Figure 2.2 Structures of photosensitizers in foods and their reactive sites.


2.3. Transition of energy in foodsPhotosensitized oxidation can proceed in either type I or II pathways. In a

type I mechanism, excited triplet photosensitizer (3Sen*) may interact

directly with a substrate molecule by accepting and donating hydrogens

andelectrons (Choe&Min, 2005).Radical compounds formed fromthe type

I pathway can abstract hydrogens from other compounds to initiate free rad-

ical reaction (Min & Boff, 2002a, 2002b). These radicals undergo further

oxidation with triplet oxygen to form hydroperoxides. Excited triplet

photosensitizer (3Sen*) may also react with triplet oxygen to form

superoxide anions in type I pathway (Kepka & Grossweiner, 1971). Under

low oxygen conditions in foods with readily oxidizable compounds,

the type I reaction pathway predominates, but this is not common

(Korycka-Dahl, Richardson, & Foote, 1978).

More than 99% of excited triplet photosensitizers (3Sen*) proceed in

type II pathway (Choe & Min, 2005). Energy is transferred from excited

triplet photosensitizer to triplet oxygen to form singlet oxygen and ground

state of a singlet photosensitizer (Fig. 2.3; Keene, Kessel, Land, Redmond, &

Truscott, 1986). Excited triplet photosensitizer and singlet oxygen possess

Fluorescence

Ground state

Singlet oxygen

Pho

spho

resc

ence

1Sen (chlorophyll, riboflavin,and myoglobin)

3Sen*

1Sen*

3O2

Intersystem crossing(ISC)

hv

Figure 2.3 Photosensitizing mechanisms.


higher energy states, while ground state singlet photosensitizer and triplet

oxygen possess lower energy states. The rate of the type II pathway is most

dependent on the solubility and concentration of oxygen present in the sys-

tem (He, 1998). The reader is directed to a comprehensive review (Choe &

Min, 2005) for detailed description of the chemistry of these pathways.

Photosensitizers present in foods are capable of forming numerous rad-

ical compounds and singlet oxygen under light exposure. These formed

compounds are very reactive and are largely involved in food oxidation

(Brand-Williams, Cuvelier, & Berset, 1995). The formation of these highly

reactive radical compounds, including superoxide (O2�•), hydroxyl radical

(OH•), peroxy radical (ROO•), and alkoxyl radical (RO•), through different

pathways under light irradiation accelerates food oxidation and has negative

impacts on overall food quality (Choe & Min, 2005).

3. THE EFFECT OF LIGHT-INDUCED OXIDATION ONFOOD QUALITY

The effects of light-induced photooxidation on foods can generally be

categorized into three main areas: quality effects, nutritional and bioactive

effects, and human health risk effects.


1. Quality effects: Light exposure leads to the formation of various volatile

compounds responsible for undesirable odors and flavors of foods as well

as causes changes in pigments and colorants, leading to observable

discoloration (Hong, Wendorff, & Bradley, 1995; Jung, Kim, & Kim,

1995; Li & Min, 1998; Min & Boff, 2002a, 2002b).

2. Nutritional and bioactive effects: Essential nutritional components (vitamins,

lipids, and proteins) of food products are lost or chemically altered during

photooxidation (Carlsen & Stapelfeldt, 1997; Dyrby, Westergaard, &

Stapelfeldt, 2001; Kerwin & Remmele, 2007). In addition, some

bioactive components recognized for providing health benefit beyond

basic nutrition may be degraded. The implication is the loss of basic

nutritional value and the loss of potential value in reducing the risk of

chronic diseases.

3. Human health risk effects: Some volatile compounds formedduring photoox-

idation of foods are known to be toxic to humans, including 1,4-dioxane,

benzene, toluene, and lipid peroxide (Min & Boff, 2002a, 2002b). Lipid

peroxide is a highly toxic compound that diffuses into the cell and can be

reduced by catalase, peroxidase, and glutathione (Halliwell & Chirico,

1993). Peroxide is toxic at low concentrations and may lead to diseases

such as immune-compromised subject and adult respiratory distress

syndrome. Other toxic compounds formed during oxidation of foods

under light exposure are carcinogens (Doniach, 1939).

Minimizing the negative effects of light on food quality, nutritional value,

and human health requires an understanding of the susceptibility of food

molecules to photooxidation and appropriate control measures for limiting

the transfer of energy to these molecules.

4. EFFECT OF LIGHT ENERGY ON SUSCEPTIBLE FOODMOLECULES

Certain classes of molecules within foods provide critical functions in

biological pathways, are essential for life, and must be provided through food

or supplement sources. Many, but not all, of these molecules are susceptible

to degradation and oxidation through the transfer of light energy. Lipids,

proteins, and carbohydrates are the three main structural components of

all living cells and act as primary macronutrients in the human diet. Lipids

and proteins are more susceptible to the effects of light, whereas there is very

little information relating photoenergy to degradation of carbohydrates


(Min&Boff, 2002a, 2002b).Vitamins, andmanyminerals, are essential for life

andmust be obtained throughdietary sources. Several vitamins are responsive

to light energy, but minerals are not (Fennema, 1996). Many bioactive

compounds have structures very similar to known photosensitizers and

may be susceptible to excitation or degradation from the transfer of energy

from light. A brief summary of these general classes is provided, but the

reader is directed to more in depth reviews where available.

4.1. LipidsLipids consist of a broad group of naturally occurring compounds, including

fats, sterols, waxes, triacylglycerols, and phospholipids. These compounds are

generally soluble in organic solvents but sparingly soluble in water. Phospho-

lipids are themain structural component of biologicalmembranes and are rich

in unsaturated fatty acids. Triacylglycerols, richly deposited in adipose tissue,

are major forms of energy storage in living organisms. Lipid signaling is an

important part of cell signaling that governs the basic cellular activities.

Although there is a broad diversity of fatty acids within food lipids,

humans have dietary requirements for a limited number of polyunsaturated

fatty acids, including linoleic (an omega-6 fatty acid) and alpha-linolenic acid

(an omega-3 fatty acid), which cannot be synthesized in human body (essen-

tial fatty acids). Omega-3 fatty acids, which include linolenic acid,

eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have been

found to possess significant health benefits (Harris, Hill, & Kris-Etherton,

2010). Linoleic and linolenic acids are rich in vegetable oils, milk, nuts,

and fish, while EPA and DHA are primarily found in algal and fish oil, fish,

and egg yolks. For more information about the oxidation of polyunsaturated

fatty acids by singlet and triplet oxygen oxidation, the reader is referred to

Bradley and Min (1992) and Min and Boff (2002a, 2002b).

Chlorophyll, which is a well-known photosensitizer naturally present in

soybean and algal oil, produces singlet oxygen in the presence of light and

triplet oxygen (Choe &Min, 2005). The oxidation of linoleic acid by singlet

oxygen leads to the formation of 1-octen-3-ol, which is responsible for the

oxidized flavor of soybean oil exposed to light and is well studied (Min &

Boff, 2002a, 2002b; Smouse & Chang, 1967). Beany or grassy odor,

resulting from photooxidation soybean oil, is attributed to 2-pentyl furan

(Smouse & Chang, 1967). Min (2000) reported that 2-pentyl furan is

formed in soybean oil in the presence of light and chlorophyll by singlet

oxygen oxidation of linoleic acid. The formation of reversion flavor in

soybean oil can be prevented by eliminating light exposure.


The interest in omega-3 rich lipids, for their potential health benefits,

has increased the number and variety of food products enriched with fish

or algal oil, which also means the unintentional addition of the chlorophyll

photosensitizer. Both EPA, with five double bonds, and DHA, with six

double bonds, easily react with singlet oxygen due to the number of highly

reactive unsaturated double bonds in each molecule (Fig. 2.4). This high

susceptibility to oxidation leads to the production of undesirable odors

and flavors after relatively short storage periods (Kaitaranta, 1992).

Jonsdottir, Bragadottir, and Arnarson (2005) correlated hexanal, 4-heptenal,

2,4-heptadienal, and nonenal with rancid and fishy flavors in bulk fish oil

exposed to light.

Overall, the effect of light energy on food lipids is mainly associated with

the formation of volatile compounds responsible for off odors and flavors of

food products. Foods containing high levels of polyunsaturated fatty acids

are susceptible to singlet oxygen oxidation from light exposure due to the

presence of double bonds. Singlet oxygen can also react with cholesterol

though the reaction rate is much slower (Doleiden, Fahrenholz, Lamola,

& Trozzolo, 1974).

Eicosapentaenoic acid (EPA)

Docosahexaenoic acid (DHA)

COOH

COOH

CH3

CH3

Figure 2.4 Structures of photosensitive molecules (lipids) in foods and their reactivesites.


4.2. ProteinsMilk, meat, eggs, fish and shellfish, cereals, and legumes are the major

sources of food proteins. The effect of light energy on food proteins is largely

associated with singlet oxygen oxidation of amino acids. Singlet oxygen

reacts primarily with three essential amino acids (tryptophan, methionine,

and histidine) and two conditional (essential in times of illness and stress)

amino acids (cysteine and tyrosine) (Michaeli & Feitelson, 1995, 1997).

These electron-rich amino acids, which contain either double bonds or

sulfur atoms in their structures, easily react with the electron-seeking

singlet oxygen (Fig. 2.5). The reaction rate between histidine and singlet

oxygen is 4.6�107 M�1 s�1 (Michaeli & Feitelson, 1994). Aspartic acid

is formed by the reaction between histidine and singlet oxygen, while

hydrogen sulfide is formed by the reaction between cysteine and singlet

oxygen (Choe & Min, 2005; Michaeli & Feitelson, 1994). Singlet oxygen

oxidation of amino acids results in the loss of functionality of food

proteins or enzymes under light exposure (Min & Boff, 2002a, 2002b).

4.3. VitaminsVitamins comprise a diverse groupof compounds that arenutritionally essential

micronutrients to humans and must be obtained from dietary sources

(Fennema, 1996). Functions of vitamins in humanbody include hormone-like

NH2

NH2

COOH

Tryptophan

O

OH

Histidine

NH

N

NH

Figure 2.5 Structures of photosensitive molecules (proteins) in foods and their reactivesites.


function, regulator of cell and tissue growth, precursor of coenzyme,

antioxidant defense system, and genetic regulation (Fennema, 1996).

Vitamins protect against diseases, and many have additional potential

health benefits for reducing the risk of chronic disease (Liu, 2003). Vitamins

are fortified or enriched into many food products to ensure adequate

amounts of vitamins are being absorbed into human body on a daily basis

(Radimer et al., 2004). Although quantitatively minor components of foods,

it is important to protect and maintain the vitamin concentrations in foods

throughout storage. However, many vitamins are sensitive to light energy;

photooxidation and subsequent degradation of vitamins present in food

products result in the loss of biochemical functionality and nutritional value

of vitamins (Bowden & Snow, 1932; Bradley & Min, 1992). A brief

discussion of riboflavin and vitamins A, C, D, and E response to light is

provided.

4.3.1 Vitamin ACarotenoids are forms of vitamin A and contribute significantly to vitamin A

activity of foods. Vitamin A plays an important role in numerous biological

activities of humans, especially associated with vision, and the conversion of

light energy for signaling of the visual center of the brain (Saam, Tajkhorshid,

Hayashi, & Schulten, 2002; Sugihara, Buss, Entel, Elstner, & Frauenheim,

2002). There is growing evidence that carotenoids in food products may

have additional bioactive functions relating to macular degeneration and

other eye diseases (Linan-Cabello, Paniagua-Michel, & Hopkins, 2002).

Carotenoids are orange-yellow pigments that occur naturally in many

living organisms, especially in photosynthetic organisms such as plants and

algae (Cogdell & Frank, 1987). Carotenoids are rich in fruits and vegetables,

including carrots, potatoes, spinach, cilantro, and cantaloupe. With

tetraterpenoid structures, molecules in this class contain numerous conju-

gated double bonds and absorb light energy for use in photosynthesis

(Fig. 2.6). Carotenoids also protect chlorophylls from photooxidation and

degradation (Wagner, Youngman, & Elstner, 1988). Lutein, a carotenoid

found in the macula of the eye, protects the macula from photodamage

by absorbing near-UV light (Krinsky, Landrum, & Bone, 2003).

One of the best-known properties of carotenoids is their ability to act as

antioxidants. b-Carotene is considered to be the most powerful physical

quencher in foods (Min & Boff, 2002a, 2002b). A singlet state carotenoid

quenches singlet oxygen to form triplet carotenoid and triplet oxygen

Ascorbic acid

HO

O

O

O

HO

HO

OH

OH

OH

a-Tocopherol

Vitamin D2

b-Carotene

Figure 2.6 Structures of photosensitive molecules (vitamins) in foods and their reactivesites.


(Beutner, Bloedorn, Hoffmann, & Martin, 2000). Carotenoids quench

singlet oxygen before singlet oxygen reacts with other food compounds,

such as polyunsaturated fatty acids (Choe & Min, 2005). The prevention

of singlet oxygen oxidation is likely to improve the oxidative stability of

food products under light exposure since singlet oxygen is more reactive

than triplet oxygen. The excited triplet state of carotenoid loses its energy

as heat and returns back to ground singlet state (Edge, McGarvey, &

Truscott, 1997). Although less likely, carotenoids are also capable of

quenching an excited triplet photosensitizer before the excited molecule

reacts with triplet oxygen to form singlet oxygen (Sies & Stahl, 1995).

The rate of singlet oxygen quenching by a carotenoid is highly

dependent on the number of conjugated double bonds within the

molecule. Carotenoids with seven or fewer conjugated double bonds are

not effective quenchers (Beutner et al., 2000).

Numerous studies have concluded that carotenoids act as antioxidants in

foods under light exposure due to singlet oxygen quenching. However,

there is a potential that carotenoids may act as pro-oxidants in edible oil

stored in dark conditions (Subagio & Morita, 2003). The interaction


between peroxy radicals and carotenoids may result in propagation of food

oxidation (Choe &Min, 2009). Detailed pro-oxidant mechanisms of carot-

enoids are still not fully understood, and more research is needed to better

understand the pro-oxidant mechanisms of carotenoids in light-protected

food products. One hypothesis is that carotenoids lose antioxidant activities

in light-protected foods due to the absence of singlet oxygen quenching.

Carotenoids in foods quench singlet oxygen under light exposure but are

reactive with other radical compounds in foods when that function is not

needed.

Photodegradation of carotenoids follows first-order behavior (Chou &

Breene, 1972). Carotenoids in trans forms can be photoisomerized and pho-

todegraded to form cis isomers and non-carotenoid degradation products

with reduced vitamin A activity (Jungalwala & Cama, 1962; Pesek &

Warthesen, 1988; Stratton, Schaefer, & Liebler, 1993).

Overall, the presence of conjugated double bonds in carotenoid struc-

tures makes them sensitive to photodegradation and oxidation, leading

to the formation of degradation compounds. Carotenoids are often used

as natural colorants in foods. Therefore, the effects of photodegradation

or oxidation on carotenoids of foods may include not only the loss of vitamin

A and antioxidant activity of carotenoids but also the discoloration of foods.

4.3.2 RiboflavinRiboflavin, also known as a water-soluble vitamin B2, plays important roles

in biological activity of human body, such as normal growth and develop-

ment, production and regulation of hormones, and formation of red blood

cells. It is the central component of flavinmononucleotide and flavin adenine

dinucleotide which act as oxidases or dehydrogenases to participate in

oxidation–reduction reaction of biological systems (Barile, Brizio, Valenti,

De Virgilio, & Passarella, 2000). Riboflavin may act as a bioactive com-

pound when added in food products, especially in baby foods (Lee &

Humbert, 1975). Riboflavin is yellow orange in color, contributes to the

color of food, and is well known for its photosensitizing activity due to

the presence of conjugated double bonds (Min & Boff, 2002a, 2002b).

Dairy products, such as cheese and milk, leafy vegetables, and soybean are

good sources of riboflavin. There are extensive reviews relating to the

photooxidation of dairy products and effects on product quality (Choe,

Huang, & Min, 2005; Duncan & Webster, 2010; Sattar et al., 1975).

Excited triplet riboflavin can undergo type I pathway of photosensitiza-

tion to form radicals and degradation compounds such as hydroxyl radical,


lumiflavin, and lumichrome (Allen & Parks, 1979; Bradley & Min, 1992;

Jung, Oh, Kim, Kim, & Min, 2007; Lee & Min, 2009; Pan et al., 2001).

Singlet oxygen formed by type II pathway of photosensitization can react

with riboflavin itself, leading to the destruction of riboflavin. The

degradation of riboflavin in foods under light exposure has adverse

nutritional impact and lowers food quality (Allen & Parks, 1979).

Riboflavin-containing food product may also lose its color under light

exposure due to photodegradation of riboflavin.

4.3.3 Vitamin CAscorbic acid, a form of vitamin C, is a water-soluble natural component

produced in a large amount in plant tissues (Fennema, 1996). Vitamin C

is an essential nutrient for humans and acts as an antioxidant by protecting

the body against oxidative stress (Bendich, Machlin, Scandurra, Burton, &

Wayner, 1986). Papaya, pineapple, kiwifruit, oranges, and kale are foods

rich in ascorbic acid. Ascorbic acid and its salt forms are commonly applied

as antioxidant food additives. Ascorbic palmitate is an ester form of ascorbic

acid with fat-soluble properties to protect fats in foods from oxidation.

Ascorbic acid is defined as “generally recognized as safe,” and there is no

restriction level of usage in the United States (Gardner & Lawrence, 1993).

The hydroxyl groups of ascorbic acid are responsible for the antioxidant

activity of ascorbic acid (Fig. 2.6; Brand-Williams et al., 1995). Ascorbic acid

in foods is a good electron donor, donating hydrogen atoms to other mol-

ecules, to reduce other food components and terminate oxidation chain

reactions. Oxidized ascorbic acid is relatively stable and will not initiate a

new round of food oxidation (Niki, 1991). Ascorbic acid also acts as a syn-

ergist with tocopherol by donating hydrogen atoms to tocopherol radical

(Hamilton, Kalu, McNeill, Padley, & Pierce, 1998; Olsen, Vogt, Saarem,

Greibrokk, & Nilsson, 2005). The regeneration of tocopherol back from

tocopherol radical leads to the reuse of tocopherol and the prevention of

tocopherol oxidation (Makinen & Hopia, 2000).

Ascorbic acid also acts as an antioxidant in light-exposed foods by

quenching singlet oxygen before singlet oxygen reacts with other food com-

pounds, similar to the function of carotenoids (Chou & Khan, 1983; Jung

et al., 1995). Singh, Heldman, and Kirk (1976) suggested that light

energy is important for the destruction of ascorbic acid. Sahbaz (1993)

reported that oxidation of ascorbic acid is very efficient in the presence of

riboflavin, light, and triplet oxygen. Sattar et al. (1975) found that

80–100% of ascorbic acid in riboflavin-containing milk was degraded


under light exposure. These findings suggest that singlet oxygen formed by

riboflavin photosensitization is able to react with ascorbic acid, leading to the

degradation of ascorbic acid. Ascorbic acid present in foods containing

photosensitizers may be degraded under light exposure.

Ascorbic acid may protect riboflavin of milk from photodegradation un-

der light exposure (Hall, Chapman, Kim, & Min, 2010). Results showed

that degradation rate of riboflavin in milk with 500 or 1000 ppm of ascorbic

acid was significantly slower than in milk with 0, 100, and 250 ppm of

ascorbic acid under light exposure. Both ascorbic acid and riboflavin contain

double bonds, and they compete to react with singlet oxygen at different

reaction rates. It is likely that the reaction rate between ascorbic acid and

singlet oxygen is higher than the reaction rate between riboflavin and singlet

oxygen so riboflavin is better protected in light-exposed milk that contains

ascorbic acid. However, light will also cause the degradation of ascorbic acid

and the formation of oxidized ascorbic acid (Kanner, Mendel, & Budowski,

1977). It is difficult to interpret the effect of light energy on the quality of

foods containing both ascorbic acid and photosensitizers. Ascorbic acid can

protect riboflavin from photodegradation, but it, in turn, is likely to be

degraded under light exposure.

Ascorbic acid is photooxidized to form dehydroascorbic acid by electron

transfer. The oxidation rate of ascorbic acid increased with increase in light

illumination (Mapson, 1962). Overall, ascorbic acid in foods may be pho-

todegraded, with loss of antioxidant activity, by quenching singlet oxygen

under light exposure. However, the quenching mechanism between singlet

oxygen and ascorbic acid may also protect other food compounds, such as

riboflavin in milk, from photodegradation and oxidation. The complexity

of interactions among molecules currently makes it difficult to predict the

preferential reactions among ascorbic acid, riboflavin, and other molecules

within foods when exposed to light.

4.3.4 Vitamin DVitamin D is a class of fat-soluble secosteroids and acts as a prohormone to

stimulate calcium absorption in the human body. It is important for normal

mineralization and bone growth. Vitamin D3 cholecalciferol and vitamin

D2 ergocalciferol are enriched in milk and infant formulas to provide a

readily available food source for preventing osteomalacia or rickets in chil-

dren and adults (Parish, 1979). Cholecalciferol is formed in human skin

upon exposure to sunlight, while ergocalciferol is formed in plant sterols

under UV light illumination (Zucker, Stark, & Rambeck, 1980). Light


energy is able to form classes of vitamin D; the dietary requirement for

vitamin D in human body depends on the extent of sunlight exposure

(Fennema, 1996).

The effect of light energy on photostability of vitamin D has been studied

(Jacobs & Havinga, 1979; Li & Min, 1998). Vitamin D is sensitive to light

due to its conjugated triene structure (Fig. 2.6). However, the effect of light

energy on photostability of vitamin D in food products is dependent on the

presence or absence of photosensitizers in foods, such as chlorophyll in

vegetable oils or riboflavin in milk, to produce singlet oxygen. Light

energy may have little effect on photostability of vitamin D in foods

without photosensitizers. Riboflavin accelerated the degradation of

vitamin D2 by over twofold in a model (water and acetone) system,

exposed to light as compared to an equivalent system without riboflavin

(Li & Min, 1998). It is likely that singlet oxygen produced by riboflavin

photosensitization reacts with vitamin D2, leading to the degradation and

isomerization of vitamin D2. Degradation products of vitamin D2 in a

light-exposed model system included 5,6-epoxide of vitamin D2,

tachysterol, lumisterol, and 7-dehydrocholesterol (Jacobs & Havinga, 1979;

King & Min, 1998). This once again demonstrates that the effect of light

energy on the stability of specific compounds in foods is largely associated

with the presence or absence of other photosensitizing food compounds.

4.3.5 Vitamin ETocopherol, a class of fat-soluble compound with vitamin E activity, is best

known for its antioxidant activity. It is synthesized only in photosynthetic

organisms and acts as a protective component. Tocopherol has also been

found to be crucial for seed storage and germination (Maeda & DellaPenna,

2007). Vegetable oils, including soybean, sunflower, and almond oil, are rich

in tocopherol. Tocopherol is also found in other food sources, such as

peanuts, asparagus, tomatoes, and carrots. Some animal fats also contain

tocopherol, however, in a much lower amount than that of vegetable oils

(Shahidi & Shukla, 1996). Commercial vitamin E supplements are marketed

for their antioxidant functions to protect cell membranes from oxidative

damage in human body. There are several good reviews of the antioxidant

functions of tocopherol in foods and in body systems (Choe & Min, 2009;

Halliwell, 1996; Kamal-Eldin & Appelqvist, 1996).

Tocopherol is sensitive to light due to its conjugated triene structure

(Fig. 2.6) and reacts irreversibly with singlet oxygen to form tocopherol

hydroperoxydienone, tocopherylquinone, and quinine epoxide (Choe &


Min, 2005). The reaction between singlet oxygen and tocopherol also

protects other food components from singlet oxygenoxidation. 5-Formyl to-

copherolwas found tobe aphotodegradation compoundof tocopherol under

light exposure (Pirisi et al., 1998). Some unknown intermediate species of

tocopherol present in very low amounts may also lead to the formation of

photodegradation compounds of tocopherol. However, Grams, Eskins,

and Inglett (1972) reported that tocopherol was insensitive to incandescent

light, while Drott,Meurling, andMeurling (1991) suggested that tocopherol

suffered from photooxidation but to a lesser extent than that of vitamin A.

Overall, tocopherol may not be that sensitive to light energy compared with

that of other photosensitive compounds in food products. Photodegradation

compounds of tocopherol exhibit little or no vitamin E activity (Fennema,

1996). The effect of light energy on photostability of tocopherol and its

antioxidant activity in food products is still mostly unknown, indicating that

more research is needed for a better understanding.

4.4. ChlorophyllChlorophyll, a green pigment present in green plants, algae, and photosyn-

thetic bacteria, is important for photosynthesis. Chlorophyll molecules,

located in photosystemswithin chloroplasts, absorb light and transfer light en-

ergy through an electron transport chain (Arnold & Azzi, 1968; Krause &

Weis, 1991). The resulting proton gradient is used to generate chemical

energy in the form of adenosine triphosphate (Avron & Schreiber, 1979).

Chlorophyll is found in all green vegetables as well as in fruits and

vegetables that are not green, although at much lower concentrations. In

addition, low levels of chlorophyll are found in many animal products,

including milk and butter, as a result of the animal’s vegetative diet. In

addition to its contribution as a food colorant, chlorophyll is likely to act as

a bioactive compound when consumed in food products. Chlorophyllin, a

derivative of chlorophyll, has been shown to prevent the formation of

carcinogenic compounds in human body (Dashwood, Breinholt, & Bailey,

1991; Tumolo & Lanfer-Marquez, 2012).

Chlorophyll comprises magnesium complexes derived from porphyrin

with pyrrole rings linked by single bridging carbons. Chlorophyll is sensitive

to light energy due to its conjugated double bond structure. It is protected

from light destruction during photosynthesis in healthy plant cells by sur-

rounding components that absorb light energy, such as carotenoids and

lipids (Fennema, 1996). Chlorophyll acts as a photosensitizer in foods in


the presence of light and triplet oxygen. Radical compounds and singlet

oxygen, formed by chlorophyll photosensitization, could react with chloro-

phyll itself, leading to photodegradation of chlorophyll, much like that of

riboflavin photosensitization. Photodegradation of chlorophyll may result

in the opening of the pyrrole ring, which is then fragmented into smaller

compounds (Struck, Cmiel, Katheder, & Scheer, 1990). Methyl ethyl

maleimide, glycerol, lactic, citric, succinic, and malonic acids have all been

reported to be photodegradation compounds of chlorophyll (Jen &

Mackinney, 1970; Llewellyn, Mantoura, & Brereton, 1990).

Chlorophyll likely acts as a pro-oxidant in food products exposed to

light, acting as a photosensitizer to produce radical compounds and singlet

oxygen. However, in vegetable oils stored without light, chlorophyll func-

tions as an antioxidant, not a pro-oxidant possibly by donating hydrogen

atoms to peroxy radicals to terminate the oxidation chain reaction, similar

to the antioxidant activity of tocopherol (Endo, Usuki, & Kaneda, 1985;

Gutierrez-Rosales, Garrido-Fernandez, Gallardo-Guerrero, Gandul-

Rojas, & Minguez-Mosquera, 1992). The exact location of donated

hydrogen atoms is still unknown and a peroxy-chlorophyll intermediate

may be involved. Lack of formation of radical compounds and singlet

oxygen by chlorophyll photosensitization may also explain the loss of

pro-oxidant activity of chlorophyll in foods stored in the dark. However,

very little information can be found associated with antioxidant or pro-

oxidant activity of other photosensitizers in foods under either light or

dark storage.

5. EFFECT OF SELECTED LIGHT WAVELENGTHS ONLIGHT-RESPONSIVE FOOD MOLECULES
AND FOOD QUALITY
The impacts of light energy on overall food quality have been well

discussed, including discoloration, the destruction of nutrients and bioactive

compounds, the production of off odors and flavors, and the formation of

toxic compounds. However, there is limited published information associ-

ated with the effect of specific light wavelengths on food quality; most of the

published information is related to dairy products (Webster et al., 2009,

2011; Wold et al., 2005). In fact, specific photoresponsive food

compounds respond to only a small portion of the spectrum. As a result,

selected light wavelengths or narrow regions of the spectra may have

different impacts on specific compounds in foods. It is valuable to


understand the effects of these narrow bands of light on specific food

compounds in order to determine the most detrimental light wavelengths

to the overall food quality and to guide packaging selection. There is

only limited published work pertaining to the effects of light wavelengths

on specific food compounds and much more research is needed to

understand the interactions that occur in complex food systems.

The UV region of light has been widely accepted as very detrimental to

food quality. Many compounds, with nutritional or bioactive (functional

food) contributions to human health or quality contributions (color, flavor,

and odor), are affected by light in the 200- to 400-nm wavelength region.

However, visible regions of light may also cause considerable damage to

some nutrients, bioactive compounds, and pigments. Many photosensitive

compounds, including carotenoids, flavonoids, ascorbic acid, riboflavin,

chlorophyll, myoglobin, and some food colorants, are found in food prod-

ucts. In addition, pharmaceutical and medical research has focused on the

effects of light wavelengths on photostability and mechanisms of targeted

compounds that could be applied in treatment of diseases (Stochel, Wanat,

Kulis, & Stasicka, 1998). Environmental scientists are interested in the effects

of light wavelengths on photodegradation of hazardous compounds that

may damage the environment, especially compounds found in waste water

(Manilal, Haridas, Alexander, & Surender, 1992). Literature from these dis-

ciplines provides additional information pertaining to photosensitive amino

acids, nitrogen-containing compounds, and tocopherols that are commonly

found in foods. A brief description of the effects of specific wavelengths on

these compounds is provided.

5.1. CarotenoidsThebroad class of carotenoids,which characteristically include yellow, orange,

and red pigments, includes xanthophyll (e.g., lutein, zeaxanthin, astaxanthin,

canthaxanthin) and carotene molecules (e.g., a-, b-carotenes, lycopene).Carotenoids are found in a variety of food sources, often contributing a natural

source of pigmentation. The effect of specific light wavelengths on the stability

of carotenoids has been relativelywell studied.Most classes of carotenoids have

maximum absorption at light wavelengths between 400 and 500 nm (Zur,

Gitelson, Chivkunova,&Merzlyak, 2000). It is likely thatUV light and visible

light, between 400 and 500 nm, are the most destructive light wavelengths to

the stability of carotenoid compounds. Carotenoids are susceptible to

photodegradation or oxidation at these light wavelengths and lose their


antioxidant activities to protect other food components from oxidation. The

loss of food color is also significant due to the degradation of carotenoid-based

pigments.

Astaxanthin and canthaxanthin are responsible for the reddish hue of

the flesh of wild salmonoids (Skrede, Storebakkent, & Naes, 1990). The

rate of degradation of these compounds is fastest at 254 nm.

Christophersen, Jun, J�rgensen, and Skibsted (1991) studied the

photodegradation rates of astaxanthin and canthaxanthin in chloroform

at 254, 313, and 436 nm. Quantum yields for photodegradation of

astaxanthin in chloroform at light wavelengths of 254, 313, and 436 nm

were 3.2�10�1, 3.1�10�2, and 1.6�10�6, while quantum yields for

photodegradation of canthaxanthin in chloroform at light wavelengths

of 254, 313, and 436 nm were 7.2�10�1, 5.0�10�2, and

4.6�10�6 mol Einstein�1, respectively. Photodegradation rate of

astaxanthin in salmonoids was faster under UV light (300–400 nm) than

that of fluorescent light (visible light>400 nm) (Christophersen, Ber-

telsen, Andersen, Knuthsen, & Skibsted, 1992). Astaxanthin concentration

in salmonoids under UV and fluorescent light was 6.2 and 8.2 mg kg�1

flesh (8.5 mg kg�1 flesh prior to storage) after 6 months of frozen storage

with polyamide/polyethylene packaging. Frozen salmonoids under UV

light illumination had higher rates in the loss of reddish color and the for-

mation of secondary volatile compounds, also with lower score in sensory

evaluation than under fluorescent light during storage period. Degradation

of astaxanthin led to decreased antioxidant function, with increased oxida-

tion of salmonoids under UV light illumination.

The UV light range is also destructive to lutein, b-carotene, and xantho-

phyll, possibly 100 timesmoreharmful than visible light (J�rgensen&Skibsted,

1990). UV light at 254 nm resulted in the fastest degradation rates of all these

three compounds in buffered solutions, compared to light wavelengths at 313,

366, 436, and 546 nm (J�rgensen&Skibsted, 1990). Photodegradation rates of

xanthophyll at 254, 313, 366, 436, and 546 nmwere 7.1�10�4, 4.4�10�4,

3.3�10�5, 2.4�10�6, and 1.0�10�6 mol Einstein�1, respectively. Visible

light at 463 nm also contributes to degradation of lutein (Kline, Duncan,

Bianchi, Eigel,&Okeefe, 2011).The effects of narrow lightwavelengthbands,

includingUV light (200–400 nm) and 50 nm bandpaths centered around 463,

516, 567, and 610 nm absorbance maxima, were studied at 25 �C on a lutein-

fortified colloidal beverage containing whey proteins, lutein, and limonene.

Lutein concentrations after 12 h at UV, 463, 516, 567, and 610 nm were

0.7, 1.5, 2.3, 2.1, and 2.2 mg ml�1, respectively (3.5 mg ml�1 under dark


condition). They concluded UV light and 463 nm wavelength regions were

the most damaging to lutein stability in lutein-fortified colloidal beverage.

Bixin and norbixin, which are commonly used as colorants in cheeses,

are apocarotenoids derived from the seeds of the annatto (achiote) tree

(Levy, Regalado, Navarrete, & Watkins, 1997). Norbixin is the water-

soluble derivative of bixin and binds to b-casein to form a stable color during

separation of the whey of cheese processing (Govindarajan &Morris, 1973).

Annatto extract (bixin) is very sensitive to UV light. Quantum yields for

photodegradation of annatto extract dissolved in a buffer solution

(pH 5.2) at light wavelengths of 313, 366, and 436 nm were 10�10�4,

4.3�10�4, and 1.9�10�4 mol Einstein�1, respectively, indicating that

UV light (313 and 366 nm) caused more photodegradation than visible light

at 436 nm (Petersen, Wiking, & Stapelfeldt, 1999).

5.2. FlavonoidsFlavonoid compounds, like carotenoids, are also pigmented, ranging in

color from yellow, red, blue, and purple. They contribute to the color of

plants, fruits, and vegetables and are used as colorants in food systems.

In plant systems, they filter UV light as well as provide pigmentation.

An accumulating research base indicates that flavonoids also have potential

bioactive function in the human body as antioxidants. In addition, flavo-

noids may have functional benefit in combating inflammation and reducing

the risk of cancer, with other potential biological values as well (Yao et al.,

2004). Flavonoids are sensitive to light energy due to conjugated double

bonds (Fig. 2.7). The effect of light wavelength has been studied directly

on anthocyanins and quercetin.

Anthocyanins are water-soluble pigments that give food products their

blue, red, and purple color and are widely accepted as safe food colorants

(Boulton, 2001). Anthocyanins are widely found in foods, especially in fruits

and vegetables, and extracts from red cabbage have been applied as natural

blue colorants in soft drinks (De Rosso &Mercadante, 2007). Anthocyanins

have hydroxyl groups attached to phenol groups, providing powerful anti-

oxidant functionality in foods and the potential for health benefits.

The natural function of anthocyanins in plant tissues is to protect cells

from sunlight damage, mainly by absorbing UV light (Chalker-Scott,

1999). Biosynthesis of anthocyanins in plant tissues is found to be light wave-

length dependent (Bishop & Klein, 1975; Downs, Siegelman, Butler, &

Hendricks, 1965). Visible light also affects color development of pears.

The anthocyanins, cyanidin-3-galactoside, and cyanidin-3-arabinoside are

OH

OH

HO

O

Quercetin

Cyanidin (anthocyanidin)

+

OH

OH

OH

HO

OH

OH

OOH

O

Figure 2.7 Structures of photosensitive molecules (flavonoids) in foods and theirreactive sites.


responsible for red color in pears (Francis, 1970). Light wavelengths between

600 and 700 nm gave more vivid colors in red pears with higher contents of

cyanidin-3-galactoside, but wavelengths between 400 and 500 nm resulted

in darker colors with lower contents of cyanidin-3-galactoside (Dussi, Sugar,

& Wrolstad, 1995). The longer light wavelengths led to increased

anthocyanin concentrations in pears for biosynthesis. That is, variation in

light wavelengths has a significant impact not only on photodegradation

but also on biosynthesis of food compounds.

Anthocyanins, which have absorptionmaxima at 278 and 517 nm associ-

ated with carbinol pseudobase and flavylium cation structures, respectively,

are sensitive to light exposure due to conjugated double bond structures

(Mazza & Brouillard, 1987a, 1987b; Stringheta, Bobbio, & Bobbio, 1992).

Photodegradation mechanisms of anthocyanins comprise numerous

reactions, including the cleavage of benzopyrylium and phenyl ring that

could lead to the formation of degraded compounds (Maccarone,

Ferrigno, Longo, & Rapisarda, 1987). UV light, in the range of 313 nm, is

detrimental to extracted anthocyanin pigments, as observed in elderberry

and red cabbage extracts. Elderberries are one of the richest sources of

anthocyanin pigments, with cyanidin-3-sambubioside and cyandin-3-

glucoside accounting for 85% of total anthocyanins in elderberries

(Bronnum-Hansen, Jacobsen, & Flink, 1985; Drdak & Daucik, 1990).

Quantum yields for photodegradation of anthocyanins, from elderberry


extract dissolved in citrate buffer solution, at light wavelengths of 313, 366,

and 436 nm were 2.1�10�4, 1.6�10�4, and 2.8�10�5 mol Einstein�1,

respectively (Carlsen & Stapelfeldt, 1997), decreasing one order of

magnitude between light wavelength 313 and 436 nm. Light wavelength

at 313 nm had the most detrimental effect on photostability of

anthocyanins (dissolved in buffer solution at pH 7) from red cabbage

extract in soft drinks (Dyrby et al., 2001). Overall results imply that

anthocyanin-colored food products should avoid exposure to light

wavelengths in the lowerUVrange (278–313 nm)andvisible light at 517 nm.

Quercetin, found primarily in plant sources, such as fruits (e.g., apples),

vegetables (e.g., onions), and herbs, has a yellow color (Bilyk & Sapers,

1986). The hydroxyl groups of quercetin are responsible for its antioxidant

activity, similar to that of anthocyanins (Pekkarinen, Heinonen, & Hopia,

1999). Therefore, quercetin is likely to act as a bioactive compound in food

products. Quercetin is believed to be responsible for protecting plants from

UV light damage through direct absorption of UV irradiation (Rozema

et al., 2002). Light energy absorbed by quercetin can be released as heat

or lead to the decomposition of quercetin (Smith, Thomsen, Markham,

Andary, & Cardon, 2000). Both UV and visible light illumination may have

impact on the photostability of quercetin in food products. However, the

most damaging light wavelengths to photostability of quercetin have not

yet been determined. UVA (365 nm) and UVB (310 nm) illumination

resulted in similar degradation pathways and oxidized compounds formed

from quercetin (Fahlman & Krol, 2009). Quercetin undergoes a slow

decomposition process to produce a mixture of C-ring-opened products.

2,4,6-Trihydroxybenzoic acid and 3,4-dihydroxybenzoic acid were the

main degradation products formed from quercetin under UV light illumi-

nation (Ferreira, Quye, McNab, & Hulme, 2002). There is also evidence

that quercetin degrades under blue light (Takahama, 1985). Visible

light wavelength may also have impact on the photostability of flavonoid

compounds in food products.

5.3. Ascorbic acidIt is well known that ascorbic acid (vitamin C), an important naturally

occurring water-soluble compound found in food products, is sensitive to

light exposure (Lee & Nagy, 1996). Ascorbic acid has a maximum absorp-

tion at light wavelength of 265 nm (Nandi & Chatterjee, 1987). Ascorbic

acid degraded faster in orange juice stored in UV (below 400 nm) than in

fluorescent (above 400 nm) light conditions (Conrad, 2002). Degradation


rates of ascorbic acid in apple juice were greater when stored in UV light

compared to supermarket fluorescent light or outdoor daylight (combina-

tion of UV and visible light) conditions (Conard, Davidson, Mulholland,

Britt, & Yada, 2005). Ascorbic acid concentration in apple juice with poly-

ethylene terephthalate (PET)/polyethylene naphthalate (PEN) packaging

decreased from 400 to 0 mg l�1 after 140 days under UV light exposure.

Apple juice became visibly lighter in color within a short length of time

when stored underUV light. Ascorbic acid-containing food products should

be protected fromUV light to maintain its antioxidant activity. Several stud-

ies also indicate that direct condensation of anthocyanins with ascorbic acid

could be responsible for photodegradation of ascorbic acid in food products

(Francis, 1985; Poei-Langston & Wrolstad, 1981).

5.4. RiboflavinRiboflavin, which is very responsive to light and acts as a photosensitizer, has

absorption maxima at 270, 380, and 450 nm (Chandrakuntal, Thomas,

Kumar, Laloraya, & Laloraya, 2006). Because milk is a natural source of ribo-

flavin and the degrading effects of light on milk are broadly recognized, there

is extensive literature on the effects of light wavelength on riboflavin. Ribo-

flavin degradation and the resulting effects on color, volatile chemistry, and

sensory quality have been studied in milk, a variety of cheeses, and butter.

Riboflavin-containing food products should be protected from UV

(200–400 nm) and visible light wavelengths between 400 and 500 nm.

UV and visible light wavelengths between 365 and 500 nm contribute to

photooxidation of milk, primarily due to riboflavin photosensitization

(Herreid, Ruskin, Clark, & Parks, 1952; Webster et al., 2009, 2011).

Webster et al. (2011) studied the effects of narrow bandwidths of light,

including 200–400 and 50 nm bandwidths with maxima at 395, 463, 516,

567, and 610 nm, on the formation of secondary volatile compounds in

ultra-high temperature milk and the aroma impact. Hexanal and pentanal

were formed in much higher amounts under UV light and the 463 nm

bandwidth; visible light bandwidths yielded aroma active compounds that

had shorter retention times and low aroma intensities, whereas UV light

and 463 nm bandwidths yielded volatile compounds with longer

retention times and higher aroma intensities. Matak et al. (2007) also

indicated UV light irradiation at 254 nm resulted in dramatic change in

sensory and chemical properties of goat milk.

The effect of light wavelength on cheeses also indicates a need for pro-

tection from UV and low range visible spectrum. Several studies have


evaluated wavelengths in the UV (366 nm) and visible (405, 436, and

546 nm) wavelength regions in Havarti (Mortensen, S�rensen, Danielsen,

& Stapelfeldt, 2003), Danbo (Andersen, Andersen, Hansen, Skibsted, &

Petersen, 2008) cheeses, and cheese spread (Hansen & Skibsted, 2000).

Riboflavin acts as an effective photosensitizer under light wavelengths at

405 and 436 nm, leading to the formation of singlet oxygen and various rad-

ical compounds, accelerating oxidation reactions, and degrading riboflavin.

Changes in volatile production, aromas, and color effects were reported

in Havarti cheese as a function of light wavelength (Mortensen et al., 2003).

Secondary volatile compounds were formed in highest amounts at light

wavelengths of 405 and 436 nm. Quantum yields in riboflavin-containing

Havarti cheese at wavelengths 366, 405, and 436 nm were 0�10�5,

5�10�5, and 3�10�5 mol Einstein�1 for hexanal and 0�10�5,

13�10�5, and 9�10�5 mol Einstein�1 for 1-pentanol (Mortensen

et al., 2003). Havarti cheese exposed to light wavelength at 366 nm retained

sweet and buttery odors while nauseating and acidic odors were detected in

Havarti cheese under light exposure at 405 and 436 nm after 24-h storage

periods. Color changes of Havarti cheese were less significant at wavelength

366 nm compared to that of 405 and 436 nm. Riboflavin was degraded only

at 436 nm in Danbo cheese exposed to light wavelengths at 366, 436, and

546 nm (Andersen et al., 2008). Riboflavin does not absorb light at 546 nm

so 546 nm did not have a direct effect on riboflavin degradation; also,

although riboflavin does absorb light at 366 nm, 366 nm did not cause

the degradation of riboflavin in Danbo cheese, which is consistent with

observations in Havarti cheese (Mortensen et al., 2003). Both studies

suggested that the energy of excited riboflavin may be transferred to other

food components, such as carotenoids, permitting riboflavin to return to

ground state without being degraded under light wavelength at 366 nm.

Although 405 and 436 nm was observed to be most detrimental to

Havarti and Danbo cheeses, 366 nm caused higher oxidation in a dairy cheese

spread (Hansen & Skibsted, 2000). Quantum yields of lipid peroxide forma-

tion in a riboflavin-containing dairy spread stored at 366, 405, and 436 nm for

12 h were 4.5�10�3, 2.6�10�3, and 1.1�10�3 mol Einstein�1, respec-

tively. Mortensen et al. (2003) suggested that the difference in responses

may be attributed to a higher b-carotene/riboflavin ratio in the dairy cheese

spread compared to the Havarti cheese. b-Carotene is known to be an effec-

tive quencher against oxidation and may have protected riboflavin and lipids

in the dairy spread against photodegradation and oxidation. b-Caroteneis more stable under visible than under UV light as we described earlier.


That is, the lower degradation of b-carotene in the dairy spread under visible

light wavelengths (405 and 436 nm) may protect riboflavin and lipid in dairy

spread against photodegradation and oxidation. The relatively small amounts

of b-carotene present in Havarti cheese would provide little protection of

riboflavin from photodegradation and oxidation under light wavelengths at

405 and 436 nm. The energy that is absorbed and transferred from one mol-

ecule to another within a complex food system is affected by the combination

of photoresponsive molecules within the food.

5.5. ChlorophyllChlorophyll acts as an effective photosensitizer under specific light wave-

lengths, similar to that of riboflavin. Chlorophyll is sensitive to light, leading

to its degradation (Psomiadou &Tsimidou, 1998). Chlorophyll absorbs light

energy and acts as a photosensitizer at 400–450 and 650 nm, forming singlet

oxygen and radical compounds. Thron, Eichner, and Ziegleder (2001) stud-

ied the effects of specific light wavelengths on sunflower oil spiked

with chlorophyll and observed the highest degree of oxidation at 650 nm.

Oxygen consumption of 15 g model system per quant under light wave-

lengths at 400, 450, 500, 550, 600, and 650 nm was 3.36, 2.54, 1.81, 4.49,

4.26, and 5.0210�23 mg, respectively. Pentane was formed at the highest

amounts at 650 nm. Lower oxygen consumption rate and pentane formation

were observed in chlorophyll-spiked sunflower oil at 400 and 450 nm than

that of 650 nm. It is implied that light wavelength at 650 nm could be most

damaging to photostability of chlorophyll in sunflower oil.

Chlorophyll is also present in dairy products but generally at very low

concentrations. Chlorophyll in cheeses was degraded under light wave-

lengths at 436 and 546 nm, but not at 366 nm (Andersen et al., 2008).

Chlorin (chlorophyll a) absorbs light energy between 500 and 633 nm

(Wold et al., 2005). Webster et al. (2011) observed that pentanal production

was high in milk exposed to light at 610 nm, suggesting that chlorophyll,

other chlorins, or a porphyrin may be contributing to oxidation of milk

in addition to riboflavin. In conclusion, food products containing chloro-

phyll may be sensitive to longer visible wavelengths, in the 650 nm range

of light, contributing to changes in volatile chemistry.

5.6. MyoglobinNumerous studies have focused on the effect of light wavelengths on meat

color. Color is an important quality factor for consumers to select and pur-

chase fresh meat. The color of meat is determined by relative amounts of


myoglobin, oxymyoglobin, and metmyoglobin (Hood & Riordan, 1973).

Myoglobin and oxymyoglobin can be oxidized to formmetmyoglobin under

photochemical reactions (Zhu&Brewer, 1998). The change in color ofmeat

from red (myoglobin and oxymyoglobin) to brown (metmyoglobin) due to

photooxidation is unacceptable to consumers. Light at 580 nmwas absorbed

by myoglobin and led to the oxidation of myoglobin and oxymyoglobin in

beef cuts (Townsend & Bratzler, 1958). They also found yellow light wave-

lengths (570–590 nm) resulted in the greatest amount of metmyoglobin for-

mation. Six different visible light wavelengths, 420, 510, 550, 570, 590, and

632 nm, were applied to study the effects on the formation of oxidized com-

pounds in myoglobin-containing meat products (Solberg & Franke, 1971).

However, results indicated that formation of oxidized compounds was not

wavelength dependence. They also suggested molecules other than myoglo-

bin and oxymyoglobin, such as riboflavin, could be involved in the formation

of oxidized compounds in meat exposed to light.

Quantum yields for photooxidation of oxymyoglobin to form

metmyoglobin in beef extract under light wavelengths at 254, 405, and

546 nmwere 1.6�10�2, 1.2�10�5, and 7�10�6 mol Einstein�1, respec-

tively (Bertelsen & Skibsted, 1987). They assumedUV light is more efficient

than visible light in metmyoglobin formation and meat discoloration; rela-

tive rates of myoglobin oxidation at 254, 405, and 546 nm were 4700, 12,

and 1, respectively. UV light wavelengths below 350 nm were found to

cause negative effects on color stability of minced beef (Andersen, Bertelsen,

& Skibsted, 1989). Setser, Harrison, Kropf, and Dayton (1973) reported that

light wavelength at 254 nm gave the greatest loss of oxymyoglobin in bovine

muscle. Lighting without UV irradiation led to a significant delay in meat

discoloration with extended shelf life (Djenane, Sanchez-Escalante, Beltran,

& Roncales, 2001). Overall, myoglobin and oxymyoglobin are sensitive to

UV and visible light wavelengths and both UV and visible light wavelengths

led to an increase in the formation of metmyoglobin in meat products (Setser

et al., 1973). Although UV light is much more detrimental to red color of

meat than visible light, myoglobin-containing meat products also should

avoid visible light exposure, especially at wavelength 580 nm.

5.7. Food colorantsBoth natural and synthetic colorants are used in foods to preserve food color

during storage. Synthetic food colorants have been largely applied in the past

few decades due to their high stability and low cost (Young & Yu, 1997).

However, recent studies suggest that synthetic food colorants could act as


carcinogens, with a risk of toxicity in the human body (Wrolstad & Culver,

2012). With strict regulation set by US Food and Drug Administration

regarding legal concentrations that may be added in food products, and

the risk of toxicological and safety concerns of synthetic food colorants, food

manufacturers are seeking stable, natural colorants for their products

(Qi et al., 2010). However, many food colorants are light sensitive.

Carminic acid is a red b-glycosyl derivative of anthraquinone that occursnaturally in the cochineal insect (Fiecchi, Galli, & Gariboldi, 1981). It is also

known as Natural Red 4 and is widely used in beverage products. Carminic

acid is sensitive to light exposure and high pH levels (Tanaka, Yamaura, &

Toba, 1986). Photodegradation rates of carminic acid are strongly wave-

length dependent, and themost detrimental light wavelengths to the stability

of carminic acid fall in the lower UV range (254–334 nm). Quantum yields

for photodegradation of carminic acid dissolved in NaCl solution at light

wavelengths of 254, 366, and 436 nm were 2�10�4, 4.6�10�5, and

2.1�10�5 mol Einstein�1, respectively (Jorgensen & Skibsted, 1991);

254 nm was most damaging to carminic acid. Amino- and hydroxyl-

substituted anthraquinones are likely to be responsible for photodegradation

of carminic acid, but detailed chemical mechanisms are still not clearly

understood (Allen, Harwood, & McKellar, 1978). The relative rates

of photodegradation of carminic acid in fruit wine at light wavelengths of

334, 366, and 436 nm were 38, 1, and 0.1, respectively, with greatest deg-

radation at 334 nm (Refsgaard, Rasmussen, & Skibsted, 1993). Carminic

acid also has a maximum absorption at 500 nm (Gonzalez, Gallego, &

Valcarcel, 2003). Therefore, beverage products with carminic acid as food

colorants should avoid exposure to light wavelengths at lower UV range or

visible light at 500 nm. Degradation of carminic acid results in the loss of red

color in food products during storage.

Saffron, a natural food colorant with intense golden-yellow color,

originates from the crocus (Tarantilis & Polissiou, 1997). Most chemical

compounds found in saffron are classes of carotenoids, such as lycopene,

zeaxanthin, and b-carotene (Tsimidou & Tsatsaroni, 1993). Therefore, saf-

fron possesses antioxidant activity due to carotenoid compounds, contribut-

ing to functionality as a food colorant and a bioactive compound in food

products. However, saffron is also sensitive to light exposure due to conju-

gated double bond structures (Orfanou & Tsimidou, 1996). Manzocco,

Kravina, Calligaris, and Nicoli (2008) concluded that the oxidation rate

of a saffron-containing beverage was faster with increased light intensity

from 0 to 8100 lux. Saffron has a maximum absorption at light wavelength


of 440 nm, attributable to trans-crocins, the main compound responsible for

golden-yellow color of food beverages (Manzocco et al., 2008). However,

the intensity of trans-crocins (440 nm) peaks decreased during increased light

intensity with the loss of golden-yellow color in beverage products. That is,

light at 440 nm may be harmful to the golden-yellow color in saffron-

containing food products due to degradation of trans-crocins. trans-Crocins

could be isomerized to less colored cis isomers or lead to the formation of

uncolored hydroperoxy-crocins (Manzocco et al., 2008; Tsimidou and

Biliaderis, 1997).

5.8. ProteinAlthough there is very limited information about light wavelength effects on

food proteins, there is some published literature on the photostability of phar-

maceutical proteins (Manning, Chou, Murphy, Payne, & Katayama, 2010).

Tryptophan, tyrosine, andphenylalanine are the amino acidsmost sensitive to

photooxidation due to conjugated double bonds in their structures, but cys-

tine, with the disulfide bond, also demonstrated some sensitivity to UV light.

Photooxidation of tryptophan, at UV light wavelengths above 300 nm,

has been involved in most photolytic damage to pharmaceutical proteins

with subsequent loss of binding and biological activity (Qi et al., 2009).

Amino acids neighboring to tryptophan were affected when tryptophan

absorbed UV light wavelengths between 320 and 400 nm (Roy et al.,

2009). Reduction of disulfide bonds in proteins may occur by electron trans-

fer when tryptophan absorbs UV light (Vanhooren, Devreese, Vanhee, Van

Beeumen, & Hanssens, 2002). A disulfide bond is a covalent bond with the

coupling of two thiol (SH) groups of cysteine. Disulfide bonds play critical

roles in protein stability by holding proteins together in its functional and

native forms (Huang, Cao, & Davie, 1993). The effect of specific wave-

lengths on photodegradation rates of cystine was studied (Asquith & Hirst,

1969). Acidic cystine solutions exposed at 248, 254, 265, 270, 280, 289, 297,

302, and 313 nm had absorbances of 0.9, 0.825, 0.577, 0.463, 0.263, 0.14,

0.07, 0.04, and 0.017, respectively. Cystine had a maximum absorption at

light wavelength 248 nm, while wavelengths above 300 nm had little or

no effect on this amino acid. Simultaneous fusion of C��S or S��S bonds

led to decomposition and deamination of cystine and the formation of deg-

radation products, including pyruvic acid, cysteine, ammonia, and cysteic

acid (Asquith & Hirst, 1969). These studies suggest that pharmaceutical pro-

teins could lose functionality under UV light by altering protein structures,

stability, and biological activities of amino acids.


Collagen, a type of protein found in animals, is associated with bone

strength and skin resilience. It contains the aromatic amino acids, phenylal-

anine, and tyrosine, which absorb light wavelength at 253 nm resulting in

irreversible destruction of these amino acid residues (Sionkowska &

Kami�nska, 1999). Changes in polydispersity of collagen were observed at

253 nm. Singlet oxygen may initiate photodegradation or oxidation of

phenylalanine and tyrosine in collagen to form active oxygen species, such

as H2O2 and O2�, which can easily attack other biomolecules. 3,4-

Dihydroxyphenylalanine was the degradation product formed from phenyl-

alanine at UV light wavelengths below 300 nm (Kato, Nishikawa, &

Kawakishi, 1995). Proteins present in food products can also be sensitive

to UV light wavelengths, similar to that of pharmaceutical proteins. The

losses of essential nutrients and functionalities of food proteins under UV

light could lower overall food quality and bioactivity. Food products should

be protected from UV light wavelengths to retain nutritional value of food

proteins during storage.

5.9. Tocopherol and retinoic acidThere has been increasing attention given to the effects of light wavelengths

on photostability and activity of bioactive pharmaceutical compounds.

Tretinoin tocoferil, which is a tocopherol-ester compound, has been used

to treat skin ulcers (Makishima et al., 1998). Tretinoin tocoferil is composed

of retinoic acid and tocopherol ester. Retinoic acid is a metabolite of vitamin

A that mediates the functions of vitamin A required for cell growth, normal

cell differentiation, and cell maintenance (Tee & Lee, 1992). Liver, eggs, car-

rots, sweet potatoes, green vegetables, and tropical fruits are foods rich in ret-

inoic acid. Tocopherol is a class of compound with vitamin E activity and is

known for its antioxidant activity as described earlier in this review. Tretinoin

tocoferil stimulates the proliferation of human skin fibroblasts due to either

retinoic acid or tocopherol activity (Makishima & Honma, 1997). However,

tretinoin tocoferil is sensitive to light (Teraoka, Konishi, & Matsuda, 2001).

A significant increase in photodegradation rate of tretinoin tocoferil occurred

at light wavelengths below 500 nm, with 420 nm as most damaging, while no

degradation products were observed at wavelengths above 500 nm. The

remaining percentage of tretinoin tocoferil at 300, 350, 400, 420, 450, and

500 nm after 1 h was 80%, 55%, 15%, 10%, 25%, and 100%, respectively

(Teraoka et al., 2001). Tocopherol has a maximum absorption at light wave-

length 292 nm, while retinoic acid has a maximum absorption at 365 nm (Jore

& Ferradini, 1985; Wang, Hodges, & Hill, 1978). However, tretinoin


tocoferil, which is composed of tocopherol and retinoic acid, was most

degraded under light wavelength at 420 nm (Teraoka et al., 2001). There

is no doubt we cannot determine the most damaging light wavelengths to

photostability of tocopherol and retinoic acid in food products based on

photostability of tretinoin tocoferil. However, we may infer that the most

detrimental light wavelengths to food products composed of numerous

food compounds and individual specific compound could be totally

different. Light wavelength at 420 nm could be most damaging to

photostability of tretinoin tocoferil composed of tocopherol and retinoic

acid, while wavelengths at 292 and 365 nm may be most damaging

to photostability of tocopherol and retinoic acid, individually. The other

possible explanation for this difference can be attributed to the

interaction of antioxidant and pro-oxidant activity. Retinoic acid acts

as a photosensitizer under UV light wavelengths, and numerous

photodecomposition products and radicals are formed (Xia et al., 2006).

Tocopherol, however, acts as antioxidant in foods under light exposure.

There could be specific light wavelengths that tocopherol is effective

to protect foods from retinoic acid-initiated photodegradation, while

tocopherol is mostly degraded and gives no protection against

photodegradation at other light wavelengths. Variation in amounts of

compounds, such as tocopherol and retinoic acid, may also affect

photodegradation and oxidation mechanisms of foods as discussed earlier

in this review. Overall, it is very difficult to determine the most harmful

light wavelengths to food products containing numerous compounds due

to a very complicated scenario. It is possible that light wavelengths in the

420 nm region could be detrimental to photostability of foods containing

tocopherol and retinoic acid.

5.10. Nitrogen-containing compoundsPyridine is a heterocyclic organic compound with a nitrogen atom and is used

in food colorant and flavoring. Pyridine is found in a relatively small amount of

foods, including milk, nuts, cereal, meats, and vegetables. Pyridine can signif-

icantly contribute to flavor properties of foods, as 2-methylpyridine and

4-isobutylpyridine are responsible for astringent and fatty flavor in food prod-

ucts (Maga, 1981). There is no reported information about photochemistry of

pyridine in foods. However, there is evidence that the drug nisoldipine, a class

of dihydropyridine, is sensitive to light (Michelitsch, Reiner, Schubert-

Zsilavecz, & Likussar, 1995). Photodegradation of nisoldipine under UV light

yielded nitrophenylpyridine and dimers of nitroso derivatives (Marinkovic,


Agbaba, Karljikovic-Rajic, Vladimirov, & Nedeljkovic, 2003). Photo-

degradation of this drug, which is used to treat angina pectoris, hypertension,

and heart failure, leads to decreased therapeutic effects and the formation of

toxic compounds (Michelitsch et al., 1995). However, the effect that light

has on pyridine-associated compounds in foods or any effects of pyridine

on human health are still uncertain. There is a potential that UV light may

be damaging to pyridine, but it is still not sure whether this directly affects food

quality, especially flavor characteristics.

Azo compounds, which include the R��NN��R0 structure, have vividcolors, including orange, red, and yellow, and account for 60–70% of all dyes

used in foods as colorants (Fennema, 1996; Gung & Taylor, 2004). We

assume that azo dyes may be sensitive to UV light illumination though

they are generally stable within foods when exposed to the wide pH range

of foods, heat, oxygen, and light. Orange II is a class of azo dye present in

industrial wastewater and is likely to be degraded under light exposure

(Faust & Hoigne, 1990). Feng, Hu, Yue, Zhu, and Lu (2003) studied the

effect of UV light wavelengths at 254 and 365 nm on photostability of

Orange II in aqueous solution. UV light at 254 nm significantly

accelerated photodegradation of Orange II and was almost completely

degraded after 30 min. Orange II was still present, but only at 10%, when

exposed to 365 nm after 90 min. Quantum yields of radicals formed from

photodegradation of Orange II increased as UV light wavelength

decreased (Kang, Liao, & Hung, 1999). UV light wavelength at 254 nm

resulted in the fastest photodegradation rate of Orange II with the highest

amounts of formed radical compounds. These radicals may be involved in

further degradation or oxidation of Orange II under light exposure. While

Orange II is an industrial dye, not a food dye, its response to UV light

may be indicative that 254-nm region wavelengths could be damaging to

photostability of azo dyes in foods. In conclusion, UV light wavelengths

could be most damaging to nitrogen-containing compounds in food

products. However, it is not clear how photodegradation of nitrogen-

containing compounds in foods affects food quality.

Foods and beverages are composed of numerous compounds in complex

matrices. The interaction between food compounds and other factors, such

as temperature, pH, water activity, and food structure, also impacts the effect

of specific light wavelengths on photostability of specific compounds present

in food products.We concluded that UV light illumination, especially in the

region of short wavelengths, can be most damaging to photostability of the

majority of compounds present in foods. However, wavelengths between


400–500 and 600–650 nm, where riboflavin and chlorophyll are excited, are

also important to consider for foods that contain these compounds. More

studies are needed for a better understanding of the effect of specific light

wavelengths on overall quality of foods.

6. FOOD PACKAGING TO PROTECT FOOD QUALITY BYINTERFERENCE WITH LIGHT ENERGY

The most effective way to protect food products from light damage is

to provide a complete light block, but this approach limits visibility of the

product to the consumer (Risch, 2009). Packaging costs may also be higher

in order to provide this level of protection. Understanding the effect of

specific light wavelengths on food compounds within a food system will

allow the development of novel, possibly tailored, food packaging materials.

For example, a packaging material that blocks UV light wavelengths below

400 nm and visible light wavelengths between 400 and 500 nm could

be applied to protect carotenoid-containing food products from

photodegradation and oxidation. This specific designed packaging would

limit exposure to the most damaging light wavelengths. However, food is

a complicated matrix containing numerous compounds, and these com-

pounds respond to light energy andwavelengths in different ways. The pack-

aging material should target the protection of those food compounds most

responsible for overall quality within the food product. Innovative food

packaging materials that reduce the intensity of light energy within focused

light wavelength regions may provide effective protection of photo-

responsivemolecules, thus protecting product integrity and nutrient stability.

Packaging films with unique optical properties through wavelength in-

terference, rather than absorption, may provide options for creating novel

food packaging that combines light protection and product visibility

(Cong & Cao, 2004; Webster et al., 2009). Milk, packaged in glass

bottles with iridescent films (blocking all UV wavelengths and either a

single visible riboflavin-excitation wavelength or all visible riboflavin-

excitation wavelengths), was exposed under fluorescent light up to 21

days (Webster et al., 2009). The use of iridescent films that blocked UV

and all riboflavin-excitation wavelengths (broad spectrum), allowing only

4% transmission at those wavelengths, provided better protection than all

other treatments (UVþ single riboflavin-excitation wavelength or a broad

spectrum film that blocked all but 20% transmission). However, the

protection was not as great as a complete light block, provided by foil


overwrap, as evidenced by an oxidized flavor by the 21st day. This suggested

that other photosensitizers, in addition to riboflavin, may be present in milk

and lead to the formationof oxidized flavor at lightwavelengthsother than the

region of riboflavin excitation. This outcome suggests that other

photosensitizers in milk may also need interference or that the transmission

needs to be less than 4% at the riboflavin-excitation wavelengths.

Ready-to-serve beverages are often packaged in transparent bottles made

of PET (Beltran-Gonzalez, Perez-Lopez, Lopez-Nicolas, & Carbonell-

Barrachina, 2008). PET is a thermoplastic polymer resin of the polyester

family with an excellent barrier property. Van Aardt, Duncan, Marcy, Long,

and Hackney (2001) demonstrated that amber PET bottles, which blocked

UV and visible wavelengths less than 450 nm, provided greater protection

than did clear PET with UV blockers for milk stored at 4 �C at

1100–1300 lux for 18 days. PET blended with small amounts of PEN

may provide better protection against light destruction (Conard et al.,

2005). The two condensed aromatic rings of PEN give better UV light

resistance compared to that of PET (Starosta, Wawszczak, Sartowska, &

Buczkowski, 1999). However, the high cost of PEN has limited its use;

blends of PETwith PENwould provide a better light barrier property while

reducing costs (Patcheak & Jabarin, 2001). Conard et al. (2005) studied

the effect of packaging material on ascorbic acid degradation rates of apple

juice under UV light exposure. Degradation rates of ascorbic acid in PET,

PETþ1% PEN, and PETþ4% PEN packaging treatment bottles were 3.2,

1.9, and 1.6 mg l�1, respectively. Blends of PET with PEN led to less

ascorbic acid degradation in apple juice under UV light exposure. PET

can block UV light wavelengths below 320 nm, while PEN is able to block

UV light wavelengths below 375 nm (Conard et al., 2005). Blends of several

packaging materials that block an extended region of light wavelengths

could provide a better light barrier property while maintaining a reasonable

packaging cost.

The effect of packaging material with either UV-permeable or UV-

impermeable characteristics on the color stability of chilled meat under light

exposure was studied (Bertelsen & Boegh-Soerensen, 1986). UV light-

impermeable packaging improved color stability of light-exposed meat.

However, UV-impermeable packaging material did not improve the color

stability of ham exposed to light (Andersen et al., 1989). It is assumed that

light wavelengths other than UV light may be responsible for photooxida-

tion of nitrosomyoglobin and the loss of red color of ham under light expo-

sure. Differences in the photochemistry between oxymyoglobin, which is


sensitive to UV light, and nitrosomyoglobin, which may be sensitive to light

wavelengths other thanUV light, needed to be further investigated. Caution

should be taken when determining photochemistry of closely related com-

pounds, such as oxymyoglobin of chilled meat and nitrosomyoglobin of

ham. These closely related compounds may be sensitive to different light

wavelengths and could have significant impact on the selection of food pack-

aging materials.

The effect of different packaging materials, including transparent-

oriented polyethylene terephthalate (OPET), transparent-oriented polypro-

pylene (OPP), cavitated white OPP, and metalized extruded OPP on lipid

oxidation in potato crisps exposed to fluorescent light was studied

(Lennersten & Lingnert, 1998). Results showed neither OPET nor OPP

provided adequate protection against light-induced lipid oxidation in potato

crisps. Cavitated white and metalized extruded OPP provided much better

protection against lipid oxidation in potato crisps under light exposure; met-

alized extruded OPP was the most effective. However, metalized packaging

materials have been largely replaced by materials that have more environ-

mentally friendly images (Lennersten & Lingnert, 1998). Transparent OPET

and OPP provide clarity to consumers to see through food products. How-

ever, they do not provide protection against lipid oxidation in foods under

light exposure. Potato crisps packed in polyethylene plus a brown light-

absorbing pigment were relatively stable throughout a long storage period

under light exposure, suggesting pigments can be used to improve the light

barrier of packaging materials (Kubiak, Austin, & Lindsay, 1982). The

choice of food packaging material not only depends on its ability to protect

food products from photodegradation and oxidation which results in a better

food quality but also depends on other factors such as cost, clarity, and

environmental issues. Food manufacturers need to select the most suitable

packaging materials for specific food products based on all the associated

factors.

7. CONCLUSIONS

Light energy plays an important role in overall food quality during

storage. Numerous compounds that occur naturally or are added to food

products absorb light energy at different wavelengths and initiate various

degradation and oxidation reactions. Photosensitizers, such as riboflavin,

chlorophyll, and myoglobin, form singlet oxygen and radical compounds

in the presence of light, while photoresponsive compounds are sensitive


to light energy and may photodegrade or undergo oxidation. The combined

effects lead to the destruction of nutrients and bioactive compounds present

in foods, the formation of undesirable off odors and flavors through oxida-

tion reactions, the loss of food color due to pigment degradation, and the

formation of toxic substances in foods under light exposure. These negative

impacts will not be accepted by consumers and can cause a significant loss to

the food industry.

There is little information on the antioxidant or pro-oxidant activity

of food antioxidants when exposed to specific light wavelengths. The effect

of light energy or wavelength on antioxidant or pro-oxidant mechanisms of

food antioxidants is still not well understood. Different photodegradation or

oxidation reactions of food compounds or food antioxidants could occur

when exposed to different light wavelengths due to the differences in energy

levels they absorb from light, leading to the production of various radicals or

oxidized compounds. The reactions between formed radicals or oxidized

compounds and food antioxidants may lead to different mechanisms of food

antioxidants. More research is needed to investigate the effect of light energy

or wavelength on antioxidant or pro-oxidant activity of food products.

Understanding the effect that specific light wavelengths have on food

compounds will allow the development of novel food packaging materials

designed to block the most damaging light wavelengths for light-sensitive

food compounds. However, there is still unknown territory associated with

the overall effect of light energy on food quality and packaging selection.

Detailed photodegradation or oxidation mechanisms of numerous food

compounds are needed, especially pertaining to the effect of light wave-

length on photochemistry of various food compounds. Interactions between

food compounds can also have impacts on the most damaging light wave-

lengths to overall food quality. Future research should focus more specifi-

cally on the effect of specific light wavelengths on the quality of food

products since there is limited published information on this particular topic.

This information can be also directly related to the selection of food pack-

aging materials to retain both high quality and visual clarity of food products

under light exposure.

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