OPTION F:FOOD CHEMISTRYF4 COLOUR

F.4.1: DISTINGUISH BETWEEN A DYE AND A PIGMENT

• Dye: Synthetic compounds which are added to food to enhance its appearance.

• Pigment: defined as naturally occurring colours found in the cells of animal and plants.

DYE PIGMENT

• Dye are soluble in water.• Composed of organic

substances.

Insoluble in water Composed of inorganic

substances

F4.2 EXPLAIN THE OCCURRENCE OF COLOUR IN NATURALLY OCCURRING PIGMENTS

Role of pigments in reflecting colour of foods into our eyes.

• A pigment is a naturally occurring colour found in the cells of plants and animals

• The pigments have colour because of their ability to reflect or emit different quantities of energy at wavelengths able to stimulate the retina in the eye.

• They absorb light in the visible region of the electromagnetic spectrum and transmit the remaining light in the visible spectrum which has not been absorbed

Examples of the common naturally occurring pigments

• Poriphyrins (Chlorophyll and Haem)• Carotenoids• Anthocyanins

F4.3 DESCRIBES THE RANGE OF COLOURS AND SOURCES OF THE NATURALLY OCCURRING PIGMENTS ANTHOCYANINS,

CAROTENOIDS, CHLOROPHYLL AND HEME.

Anthocyanins Carotenoids Chlorophyll Haem

1) Source

Most widely occurring pigments in plants

Most widespread pigments in nature (the large majority are produced by algae)

Plants, algae, and cyanobacteria

Fresh meat

1) Colour range

Yellow to red orange Red astaxanthin

(complexed to a protein) is responsible for the blue or green colour of live lobster and crabs, and pink colour of salmon and flamingo

Green

Red (myoglobin responsible for the colour of fresh meat)

1) Examples

Fruits and vegetables (cranberries, blueberries, strawberries, and raspberries

Banana, carrots, tomatoes, watermelon, peppers, and saffron.

Green plants

Meat of adult mammals (cows, sheeps, horses)

F4.4 DESCRIBE

THE FACTORS THAT AFFECT THE COLOUR STABILITY OF

ANTHOCYANINS,CAROTENOIDS, CHLOROPHYLL AND HEME

THE FACTORS THAT AFFECT THE COLOUR STABILITY OF ANTHOCYANINS

• The structure and colour of anthocyanins changes with pH.

• The flavylium cation is bright red in acidic. In basic solution, H+ removed from the OH group on the left ring to form a quinoidal base which is blue. As the colour of anthocyanins is pH dependent, they can be used as acid-base indicator.

• In aqueous solution, anthocyanins can exist in four possible structural forms depending on the pH and temperature.

(A) (AH⁺) (B) (C) quinonoid flavyium carbinol base chalcone (blue) (red) (colourless ) (colourless)Very high pH Low pH Neutral pH• At low pH, the AH⁺ predominates and the

mixture is red, at neutral pH values there is sufficient concentration of OH ions for this to hydrolyse and the solution becomes colourless as it is converted to B and C. At greater pHs the AH⁺ in eqm with this is converted to A and the solution turns to blue and form this product

• As the stability of anthocyanins is also affected by the temperature, the colour of anthocyanins can vary significantly during the cooking process.

• The anthocyanins is most stable and most highly coloured at low pH and low temperature.

• When exposed to heat the eqm moves to the right and the compounds are less thermodynamically stable. This causes a loss of colour and browning.

• The anthocyanins also form deeply coloured coordination complexes with Fe3+ and Al3+ ions that are present in metal cans and this lead to discolouration in canned fruit.

THE FACTORS THAT AFFECT THE COLOUR STABILITY OF CAROTENOIDS

• Carotenoids are highly unsaturated molecule and the presence of carbon-carbon double bonds makes them susceptible to chemical attack.

• Degradation pathways include isomerization, oxidation and decomposition of the carotenoids molecule.

• Light, enzymes and reaction with hydroperoxides (from the oxidation of lipids) causes oxidation that will results in the bleaching of colour, unpleasant off odours and loss of vitamin A activity

• Carotenoids are stable up to 50°C and in the pH range 2 – 7 and therefore not degraded by most forms of food processing. When heated the naturally occurring trans- isomer rearranges to the cis- isomer.

THE FACTORS THAT AFFECT THE COLOUR STABILITY OF CHLOROPHYLL

Chlorophyll contains a group with 4 nitrogen atoms which is called a porphin. The porphin ring forms a very stable complex with Mg ion.The stability of chlorophyll towards heat depends on the pH.In a basic solution with a pH of 9 it is thermodynamically stable but in acidic solution with a pH of 3 is unstable.

• When heated, the cell membrane of the plant deteriorates releasing acids which decrease the pH.

• At this lower pH, the 2 H ions will displaces Mg ion resulting in formation of an olive-brown pheophytin complex.

• The breakdown of the cell during heating also increases the susceptibility of chlorophyll to decomposition by light (photo-degradation).

THE FACTORS THAT AFFECT THE COLOUR STABILITY OF HEME

• In muscles, heme is associated with the purple –red protein myoglobin molecule, which binds to oxygen molecules to form the red oxymyoglobin molecule.

• The Fe2+ is more stable than Fe3+ in the non-polar environment provided by the side chain in the complex.

• The red oxymyoglobin undergo a slow auto-oxidation reaction to form the complex of the Fe3+ known as metmyoglobin (brown red).

• To reduce this happen, meat are packed in plastic films with low gas permeability and stored in an atmosphere of carbon dioxide.

MbO2(red,Fe2+) Mb(purple-red,Fe2+) MMb(brown,Fe3+)

Oxymyoglobin myoglobin metmyoglobin

ANTHCYANINS CAROTENOIDS CHLOROPHYLL HEME

Oxidation Affects position of equilibrium

Unsaturated carbon bonds allow for oxidation catalyzed by light, metals and hydroperoxides =LOSS of color (bleached)

*Loss of Vit. A activity = stinky

Oxygen binds to purple-red myglobin (Mb), forming red oxymyoglobin (MbO2)*Fe2+ in MbO2 and MbAuto-oxidation of MbO2 and Mb = Fe2+ → Fe3+ (metmyoglobin, MMb) = brown-red color

Temperature Higher temperatures = equilibrium shifts to the right =LOSS of color

Stable up to 50°CTherefore, 50°C+ = LOSS of color

Increase heat = trans- isomer rearranges tocis-isomer

Stability depends on pHHigh pH (basic) – about pH 9 = thermodynamically stable

Low pH (acidic) – about pH 3 = thermodynamically unstable (LOSS)

Increase heat = deterioration of cell membrane = decreases pH = chlorophyll decomposition by light

pH levels Low pH levels = greater color

Stable in range of pH 2 – pH7Therefore, pH < 2 and pH > 7 = LOSS of color

Refer to temperature

Presence of metal ions

Can form complexes with Al3+ and Fe3+ (in tin cans) = LOSS of color of canned foods

Structure of chlorophyll contains porphin ring (group with 4 nitrogen atoms) which forms complex with a Mg ionLow pH = Mg ion displaced by 2 H ions =olive-brown pheophytin color

Porphin ring forms complex with Fe ion.Fe2+ in MbO2 and Mb

F.4.5: Discuss the safety issues associated with the use of synthetic

colorants in food.

Concerns:• Synthetic dyes are biochemically active– Can negatively impact health• toxicity is easy to prove • chronic health effects are difficult to determine• Special concern about carcinogenic effects

– Standards vary from country to country• Malachite green and sudan red are generally banned

• Synthetic colorants = dyes

International Numbering System (INS) or E numbers = food additive identifiers

Artificial dyes are potentially carcinogenic (any substance, radionuclide, or radiation that is an agent directly involved in causing cancer) so these particular carcinogens are banned in certain countries.

Therefore in most countries, all ingredients are required to be on packaging labels.

International Food Concerns: Some dyes banned in certain countries but not others. Now with lots of international trade, it has become a concern with the use of these particular dyes.

Possible solution: international legislation on colorant legislation Example of International Food/Colorant Concern: Sunset Yellow in M&M's Banned in Finland and Norway

• Potential carcinogen• Allergic reaction in people with aspirin intolerance

F.4.6: COMPARE THE PROCESSES OF NON-ENZYMATIC BROWNING AND CARAMELIZATION

What is enzymatic browning process?A chemical process which occurs in fruits and vegetables containing the enzyme polyphenoloxidase and produce brown pigments.

MAILLARD REACTION• Is a type of non-enzymatic browning which consist of a complex

series of reactions between amino acids and carbohydrate.• Responsible for the smell and colour change of common cooking

processes.• the first step in Maillard browning is condensation reaction of the

aldehyde group in the reducing sugars with the free amino group of an amino acid.

• leads to the replacement of a C=O bond in the aldehyde group by C=N-R bond and the formation of water.

• Reducing sugar + amino acid → initial condensation product + water• Condition: Occur at a faster rate when the temperature is high, siza

of sugar.

CARAMELIZATION• process which involve the oxidation of with high carbohydrate

concentration, (sugar) and it is used extensively in cooking which result for the product to be brown in colour and have nutty flavour.

• This process occurs when sugar are heated at high temperature. • The compound are dehydrated and double bonds are introduced

into the structure.• The small sugar molecules react together to form polymers with

conjugate bonds which absorb light and thus producing the brown colour.

• Equation: Cn (H2O)n → n C + n H2O• Conditions: extreme pH value, type of sugar used.

F5 : GENETICALLY MODIFIED FOODS

GENETIC ENGINEERING

• Genetic engineering is important especially to food scientists to alter the properties and processing conditions of foods.

• Genetic engineering involves the alteration of the DNA.

• In the past, to improve the quality of genes, cross breeding was done. But this method is inaccurate and time consuming.

EXAMPLE

• GM corn produce a poisonous compound to reduce the dependency on pesticides and herbicides.

• GM hens produce eggs containing human

interferone

• GM cow produce milk rich in nutrients.

WHAT IS GENETICALLY MODIFIED FOOD?

A genetically modified food is food that derived from or produced by genetically

modified organism

BENEFITS OF GMO FOODS

GM foods can have improved flavor, texture and nutritional

value

GM foods can have a longer shelf life

GM organisms can be more resistant to diseases and pests

Genetic modification can increase crop yields in plants and feed

efficiency in animals

GM plants can be more resistant to herbicides and fungicides

Environmentally ‘friendly’ bio-herbicides and bio-insecticides can be produced

GM foods can lead to soil, water and energy conservation and can

improve natural waste management

Genetically modification can enable animal and plant to

produce high amount of substance that can benefit the

humans and lower the substances that are detrimental

to health

GM plants can grow in wider range of climatic condition

POTENTIAL CONCERNS USING GM FOODS

Links to increased allergies

Risk of changing the composition of a balanced diet by altering the

natural nutritional quality of foods

The pollen from GM crops may escape and pollinate natural

crops and so damage the natural ecosystem