1. Biodeterioration of fruit juices and fruit juice

concentrates

2. Microbial spoilage of wine, beer and other

fermented beverages

3. Microbial deterioration of plant pectin and the

development of soft rot in fruit and vegetables

4. Microbial spoilage of milk

5. Microbial spoilage of raw sugar and sugar confectionery

Microbial Deterioration of Plant Pectin and the Development of Soft Rot in Fruit and Vegetables

Pectic Substances

A group of polysaccharides made up primarily of sugar acids. They are important constituents of plant cell walls and the middle lamella between adjacent cell walls. Normally they are present in an insoluble form, but in ripening fruits and in tissues affected by certain diseases they change into a soluble form, which is evidenced by softening of the tissues.

They have multifunctional properties:

• Control cell wall integrity and porosity,

• Protect plants against phytopathogens,

• Have gelling, emulsifying, stabilising, thickening and health-beneficial properties.

Types of Pectic Substances

1. Protopectin A water-insoluble polymer that gives pectic acid on hydrolysis

2. Pectic acid A high-molecular-weight polymer of galacturonic acid units, with no methoxylgroups, in which all the units are free

3. Pectinic acid A polygalacturonic acid with some of its carboxyl groups methylated. It has a low methoxyl value and forms gels with sugars and water.

4. Pectins Water-soluble pectinic acids containing about 6-7% methoxyl that form gels with sugars and acids

• All fruit and vegetables contain plant pectins.

• Plant pectins are a mixture of polysaccharides from

polymers of anhydrogalacturonic acid residues in

which the carboxyl groups may be methylated.

• In a typical plant pectin, galacturonic acid residues

are linked by a-1-4 glycosidic bonds in a chain to

which chains of rhamnose and galacturonic acid are

bound and carboxyl groups are esterified to methanol

in a random manner.

Pectins

Pectin Backbone Structure

Schematic Structure of Pectin

Pectin consists of four different types of polysaccharides

Harholt J et al. Plant Physiol. 2010;153:384-395

©2010 by American Society of Plant Biologists

Kdo, 3-Deoxy-d-manno-2-octulosonic acid; DHA, 3-deoxy-d-lyxo-2-heptulosaric acid

The bioterioration of pectins is carried out by a mixture of biodeteriogen-produced pectolytic enzymes, of which there are three main classes.

1. Polygalacturonidases

2. Pectin transeliminases

3. Pectin esterases

Polygalacturonidases

• Polygalacturonide glycanohydrolases

• Hydrolyze the a-1-4 glycosidic linkages between galacturonicacid residues

• Have two subgroups that differ in substrate specificity and mechanism involved.

1. Exo-polygalaturonidases

Polygalacturonidase Polymethylgalacturonidase

2. Endo-polygalacturonidases

Endo-polygalacturonidase Endo-polymethylgalacturonidase

Pectin transeliminases

• Pectic lyases

• Cleave the a-1-4 glycosidic bonds between galacturonic acid residues by the transelimination of a proton from carbon atom 5 of the anhydromethylgalacturonate residue together with the oxygen of the adjacent atom of the a-1-4 glycosidicbond, to give a methyl galacturonide with a double bond between carbon atoms 4 and 5.

Pectin esterases

• Hydrolyze methyl ester groups to give free carboxyl groups and methanol

• Most microorganisms produce AT LEAST ONEpectolytic enzymes.

• Almost all fungi and many bacteria contain pectolyticenzymes that readily degrade pectin layers that bind the individual cells of fruit and vegetable tissue together into mixtures of oligosaccharides and galacturonic acids, a process that destroys the structural organization of plant tissue, which then becomes a soft amorphous mass.

• This degradation of pectin layers in plant tissue is responsible for the spoilage process known as “soft rot” in fruit and vegetables.

Soft Rot Microorganisms Associated with Rotting Fruits and Vegetables

Apples Bacillus polymyxa

Citrus fruits Penicillium spp.

Grapes Rhizopus nigricans

Plums Yeast

Raspberries Rhizopus stolonifer

Strawberries Bacillus cereus

Tomatoes Byssochlamys fulva

Carrots Erwinia carotovora

Celery Sclerotinia sclerotiorum

Some strains of S. sclerotiorum produce photodynamic toxins, 8-methoxy psoralen and 4,5,8-trimethyl psoralen, which are responsible for dermatitis among celery harvesters.

Microbial Deterioration of Milk

• Microbial spoilage of milk is a well-known phenomenon, milk being a perfect medium for microbial growth.

• To prevent milk spoilage, heat treatment is a standard procedure in milk processing, i.e., pasteurization (i.e., LTHT, HTST, UHT)

• Pasteurization is normally sufficient to destroy all bacteria in milk. However, even after this process, contamination by nonpathogenic bacteria may still occur, causing spoilage.

Milk microbial spoilage defects

• Production of lactic acid (souring)

• Gas production

• Development of a viscous ropy texture

• Coagulation of milk proteins

• Lipolysis of milk fats (rancidity)

• Development of off-flavors

Predominant causal organisms: lactic-acid-producing bacteria, which ferment lactose to lactic acid.

Common lactic-acid-producing milk spoilage organisms

• Homofermentative species (produce only lactic acid)

Streptococcus lactis, S. cremoris, Lactobacillus casei, L. acidophilus, L. plantarum, L. helveticus, L. bulgaris

• Heterofermentative species (produce lactic acid, acetic acid, ethanol, CO2)

L. brevis, L. buchneri, L. fermenti, L. thermophiles, Leuconostoc citrovorum, L. mesenteroides, Microbacteriumlacticum, Micrococcus luteus, M. varians, M. freudenreichii

Steps in lactose metabolism by lactic-acid-producing milk spoilage organisms

1. Hydrolysis of lactose to galactose and glucose by lactase

2. Conversion of galactose to glucose via a galactose inverting system, catalyzed by glucose-4-epimerase.

3. Utilization of glucose to produce more galactose, which serves as an intermediate for the conversion of galactose-1-phosphate to glucose-1-phosphate, catalyzed by hexose-1-phosphate uridyl transferase.

4. Conversion of glucose-1-phosphate to glucose-6-phosphate by phophoglucomutase

5. Metabolism of glucose-6-phosphate to pyruvate via the EMP pathway.

6. Reduction of pyruvate to lactic acid by lactate dehydrogenase.

1. Lactose Galactose and Glucose

2. Galactose Galactose-1-phosphate D-UDP-galactose D-UDP

glucose

3. D-UDP-glucose D-Galactose-1-phosphate D-UPP-galactose +

D-Glucose-1-phosphate

4. Glucose-1-phosphate Glucose-6-phosphate Pyruvic acid

5. Pyruvic acid Lactic acid

Scheme of Lactose Metabolism

glucose-4-epimerase

phosphoglucomutase EMP pathway

lactate dehydrogenase

hexose-1-phosphate uridyl transferase

lactase

Hydrolysis of lactoseScheme of lactose metabolism

1. Lactose Galactose and Glucose

2. Galactose Galactose-1-phosphate D-UDP-galactose D-UDP

glucose

3. D-UDP-glucose D-Galactose-1-phosphate D-UPP-galactose +

D-Glucose-1-phosphate

4. Glucose-1-phosphate Glucose-6-phosphate Pyruvate

5. Pyruvate Lactic acid

Scheme of Lactose Metabolism

glucose-4-epimerase

phosphoglucomutase EMP pathway

lactate dehydrogenase

hexose-1-phosphate uridyl transferase

lactase

Glucose-6-phosphate Pyruvate

phosphoglucomutase EMP pathway

Lactic acid

lactate dehydrogenase

NADH

NAD+

Microbial Deterioration of Raw Sugar and Sugar Confectionery

The principal effect of microbial deterioration of raw sugar is the LOSS OF SUCROSE, due to the inversion of sucrose to fructose and glucose by invertase-producing yeasts and fungi, as catalyzed by invertase.

NOTE: This results in a reduction in sucrose

content.

The susceptibility of raw sugar to microbial attack depends on the composition of the molasses film on sugar crystals, particularly on the water activity of the sugar.

Most sugars have aw = 0.60-0.75; thus, only osmophilic yeasts (aw = 0.60) and xerophilicfungi (aw = 0.65) are the main contaminants of raw sugars. This is helped by the slightly acidic pH (5-6) of sugars, which inhibits bacterial growth.

• Fungi

Aspergillus niger Penicillium expansum

Alternaria brassicae Aspergillus flavus

Monilla nigra Cladosporium herbarum

• Yeasts

Hansenula anomala Saccharomyces cerevisiae

Candida utilis Pichia fermentans

• Bacteria

Bacillus subtilis B. megaterium

Clostridia nigrificans C. thermosaccharolyticum

Microorganisms Associated with Biodeterioration of Raw Cane Sugars

• Airborne contamination

• Waterborne contamination

• Infected sugar residues

• Unsuitable storage conditions

Sources of microbial infection

• Microbial deterioration of

carbohydrates

• Microbial deterioration of

proteins and protein foods

• Microbial deterioration of

edible oils and fats

PROTEINS are large biological molecules

or macromolecules consisting of one or more

long chains of amino acid residues.

The term comes from the Greek word proteios,

meaning “primary”, “in the lead” or “standing in

front”.

• Essential to all life

• They are the major constituents of enzymes,

antibodies, many hormones and body fluids such

as blood, milk, and egg white.

Of the many kinds of food spoilage, the

microbial spoilage of proteins and protein

foods is the most complex and perhaps the

least understood, owing to the enormous

complexity of structural proteins in nature

and the wide variety of spoilage

microorganisms associated with protein spoilage.

1. Myoglobin

2. Myofibrillar proteins

3. Collagen

4. Elastins

5. Keratins

Structural Proteins of Protein Foods

• An iron- and oxygen-binding protein found in the muscle

tissue of vertebrates in general and in almost all mammals.

• Is formed from one polypeptide chain and one heme

molecule.

• Heme is a pigment responsible for the color of red meat;

thus, the color that meat takes is partly determined by the

degree of oxidation of myoglobin.

• Degraded by microbial proteases to amino acids and

oligopeptides

Myoglobin

• Consist mainly of actomyosin and form the major part of

muscle proteins.

• Degraded by trypsin-like microbial proteinases

Myofibrillar proteins

• Found in connective tissues such as tendons and bone cartilage

• Very resistant to degradation

• Contain a high proportion of nonpolar amino acids (valine, leucine,

and isoleucine, with proline and hydroxyproline groups) but no

cysteine

• Degraded by collagenases from Clostridium

Clostridiopeptidase A Hydrolyzes glycylprolyl bonds and has

pH optima of 7.7-8.0. Activated by Ca and inhibited by EDTA.

Clostridiopeptidase B Cleaves peptide bonds adjacent to

lysine and arginine and has pH optima in the range of 7.2-7.4.

Specific for collagen and gelatin.

Collagen

• Found in connective tissues such as tendons and ligaments

• Contain 90% nonpolar amino acids arranged in a random

structure

• Highly resistant to hydrolysis, heat, and maceration

• Degraded by elastinases, which have been isolated from

Flavobacterium elastolyticum, Aeromonas salmonicida, Bacillus

subtilis, Pseudomonas aeruginosa, and P. mallei

• These elastinases have the following characteristics:

Have pH optima in the range of 7.0-9.0

Hydrolyze peptide bonds adjacent to glycine and proline

Highly specific for elastin

Inhibited by diisopropylfluorophosphate

Elastins

• The major constituents of wool, hair, nails, hooves, and fish scales

• Contain large amounts of glycine and proline with about 8%

cysteine.

• Degraded by keratinases, which have been isolated from

Streptomyces fradiae and S. microflavus. They have the following

characteristics:

Have pH optima in the range of pH 8.5-9.0

Degrade keratin

Activated by calcium and magnesium ions

Inhibited by EDTA

Keratins

In general, most bacteria are unable to colonize pure proteins unless sufficient peptides, amino acids and vitamins are present to enable them to produce proteases necessary for protein digestion. Food such as meat, fish, and cheese contain abundant quantities of amino acids and other nutrients; they are therefore readily colonized by most microorganisms.

1. Putrefaction

Characterized by the production of foul odors and offensive

textures and flavors, which arise from spoilage metabolites

that result from the catabolic metabolism of low-molecular-

weight peptides and amino acids by spoilage organisms.

2. Degradation of protein constituents

Indicated by protein coagulation and liquefaction, rot

development, and destruction of structural proteins such as collagen and elastin.

Principal Changes Associated with Protein Spoilage

1. Initial contamination and colonization of the protein food by microorganisms.

2. Rapid utilization and metabolism of low-molecular-weight compounds such

as amino acids, dipeptides, lactic acid, and sugars present in meat or fish

juices, which yield spoilage metabolites, e.g., cadaverine, putrescine, organic

acids, CO2, H2S and NH3. At this stage, there is explosive microbial growth.

3. Increased production of microbial proteases by proteolytic spoilage

microorganisms. The proteolytic breakdown of high-molecular-weight proteins

to oligopeptides provides a continued supply of nutrients. The oligopeptides

are then hydrolyzed to free amino acids, which are then metabolized to

additional metabolites. This accumulation of metabolites eventually poisons the microorganisms themselves, slowing down the putrefactive processes.

Stages in the Protein Spoilage Process

Analysis of putrefied protein foods shows that a mixture of amines are

produced by the anaerobic decarboxylation of amino acids. Such

amines include the following:

1. Cadaverine from L-lysine by Bacillus cadaveris, E. coli, and

Clostridium histolycum

2. Putrescine from L-ornithine by Clostridium septicum and C. welchii

3. Aminoburyic acid from glutamic acid by S. faecalis

4. Isobutylamine from L-valine by Proteus vulgaris and Pseudomonas

cocovenans

5. Tyramine from tyrosine by S. faecalis

6. Tryptamine from tryptophan by S. faecalis and C. welchiiNOTE: All reactions are catalyzed by decarboxylases.

Amines Produced during Protein Spoilage

1. Pyruvate from alanine by Bacillus subtilis, as catalyzed by

alanine dehydrogenase (NAD-dependent)

2. -Methyl-α-ketovalerate from isoleucine, as catalyzed

isoleucine oxidase

3. Indole from tryptophan to by E. coli and Proteus vulgaris

4. α-Ketoglutarate from glutamate by E. coli, S. cerevisiae, C.

sporogenes, as catalyzed by glutamate dehydrogenase

5. Fumarate from aspartate by E. coli, as catalyzed by

aspartase

6. Pyruvate from serine, as catalyzed by serine dehydratase

Organic Acids Produced during Protein Spoilage

7. α-Ketobutyrate from threonine, as catalyzed by threonine

dehydratase

8. Pyruvate from cysteine, as catalyzed by cysteine desulfhydrase

9. Acetate from pyruvate by L. delbrueckii, Proteus vulgaris, and P.

fluorescens

9. Acetate from alanine and glycine by C. sporogenes

10. Isobutyric acid from valine and alanine

11. Isovaleric acid from leucine and alanine

12. Methylbutyric acid from isoleucine and alanine

13. Aminovaleric acid from proline

14. Aminohydroxyvaleric acid from hydroxyproline

Organic Acids Produced during Protein Spoilage

During the putrefactive process, anaerobic clostridia such

as Clostridium butyricum, C. pasteurianum, C. acetobutylicum

and C. sporogenes also produce large amounts of H2 via the

reduction of hydrogen ions or protons as catalyzed by a specific

hydrogenase requiring reduced ferredoxin as its cofactor.

2 H+ H2

Other bacteria produce hydrogen and carbon dioxide from

glucose, which is then degraded to pyruvate via the EMP

pathway, which is then converted to acetate, formate and CO2.

Ferredoxin

Fe3+ Fe3+

• In the late stage of putrefaction, spoilage microflora

also produce proteinases that degrade various

protein constituents by hydrolyzing peptide bonds

to give low-molecular-weight oligopeptides and

free amino acids.

• Spoilage microorganisms also utilize muscle

glycogen to produce trimethylamine, ammonia and

dimethylamine, whose chemical determination

forms the basis of several methods for determining

fish and fish product spoilage.

The pH optima of collagenase, elastinases, and

keratinases lie in the alkaline range, i.e., 7.2-9.0;

thus, the degradation of collagens, elastins, and

keratins in protein foods is favored during the

advanced stages of putrefaction when the various

putrefactive amines such as cadaverine and

putrescine produced increase the pH of the food

from 5.5 to above 8.0 when proteolysis has

become extensive.

During extensive proteolysis, both bacterial

and fungal proteolytic enzymes hydrolyze

casein proteins, elastins, gelatins and collagens.

• Microbial deterioration of

carbohydrates

• Microbial deterioration of

proteins and protein foods

• Microbial deterioration of

edible oils and fats

FATS are a wide group of compounds composed of long-

chain organic acids, called fatty acids. A typical fat molecule

consists of glycerol combined with three fatty acids, i.e., it is

a triol (i.e, it has three chemically active -OH groups). Fats

are formed when each of these three -OH groups reacts

with a fatty acid, resulting in triglycerides.

• Hydrophobic, and generally soluble in organic solvents

but insoluble in water.

• Shorter-chain fats are usually liquid at room temperature,

whereas longer-chain fats are solid.

NOTE: Fats differ from carbohydrates and proteins in that they are not polymers

of repeating molecular units

“Oil”, “fat”, and “lipid” are often used

interchangeably. Of these, lipid is the

general term. Oil is the term usually

used to refer to fats that are liquid at

room temperature, while fat to those

that are solid at room temperature.

In fat-containing foods, the biodeterioration of

edible oils and fats by bacteria and fungi is the

principal cause of spoilage indicated by the

following:

Rancidity

Acidity

Soapiness

Off-flavors

Discolorations

Butter is an emulsion of water in butterfat of the following

composition: 80-83% butterfat

16% water

1% nonfat milk solids

0-3% sodium chloride

Margarine is also a water-in-fat emulsion:

80% fat (a mixture palm, coco and marine oils)

20% water

Both are subject to microbial spoilage characterized by rancidity,

acidity, off-flavors and discolorations.

Butter and Margarine

1. Autooxidative deterioration

• Oxygen absorption and oxidation of unsaturated fatty acids (e.g.,

linoleic, linolenic and arachidonic) to hydroperoxides, which are

oxidized to ketones and aldehydes.

• Generally occurs during prolonged storage at ambient temperature

• Catalyzed by cupric and ferric ions, UV and high storage

temperatures (>5°C)

2. Lipolysis of natural and synthetic triglycerides in fats

• Effected by milk and microbial lipases

• Prevented by pasteurization of milk and heat treatment of butter

3. Lipoxidation

• Hydroperoxide production by specific microbial lipoxidases.

Causes of Butter and Margarine Rancidity

Butter and margarine rancidity is generally associated with lipolytic molds and yeasts.

Aspergillus tamari A. chevalieri

Cladosporium suaveolens Cladosporium butyri

Candida lipolytica Ospora lactis

Paecilomyces aureocinnamoneum Pseodomonas fluorescens

Margarinomyces bubaki Penicillium glaucum

Epicoccum purpurescens Micrococci

Microorganisms Associated with Butter and Margarine Rancidity

Rancidity and acidity are caused by the production

of free fatty acids, particularly butyric, caproic, caprylic

and capric acids, and their corresponding methyl

ketones. These volatile free fatty acids and methyl

ketones directly arise from the metabolism of liberated

free fatty acids by -oxidation to the corresponding -keto

acid, which is decarboxylated to methyl ketones or is

cleaved to give acetyl-coA and a lower fatty acid that is

two carbons shorter.

Secondary alcohols are also formed by the

reduction of various methyl ketones.

On the other hand, characteristic soapy flavors are

produced by the liberated lauric and myristic acids that

are present as triglycerides in butterfat and coconut

oils.

Factors Affecting Microbial Growth in Food

1. Temperature

2. Water activity

3. Humidity

4. pH

5. Oxygen availability

6. Osmotic pressure

Temperature

Storage temperature is considered the most important factor that affects food spoilage, as it determines the type of microfolora that will cause spoilage; however, the relative humidity and availability of oxygen must also be controlled.

Microorganisms have been reported to grow over a wide temperature range, the lowest being −34°C and the highest being 90°C. All microorganisms, however, have an optimum temperature as well as a range in which they will grow. This preference for temperature forms the basis of dividing microorganisms into the following groups:

Psychrohiles Psychrotrophs Mesophiles Thermophiles

Types of Organisms by Growth Temperature

Psychrophiles Grow best between -2 and 7°C

Psychrotrophs Optimum growth from 20 to 30°C, but can grow at ca. 7°C

Mesophiles Optimum growth at 30–40°C, but can grow between 20 and 45°C

Thermophiles Optimum growth between 55 and 65°C, but can grow at temperatures as low as 45°C.

Just as molds can grow over a wide range of pHsand moisture contents, they can also tolerate a wider temperature range than bacteria. Many molds can grow in the refrigerator. Yeasts are not usually found growing in the thermophilictemperature range, but prefer psychrotrophic and mesophilic temperatures.

Temperature

Microorganisms cannot grow in a water-free environment,

as enzyme activity is absent and most chemical reactions

are greatly slowed down. Fresh vegetables, fruit, meat, fish

and some other foods naturally have a high moisture

content, averaging about 80%. Drying is one of the oldest

methods of food preservation as it reduces moisture

availability, thereby limiting the number and types of

microorganisms that can grow and reducing the rate at

which they can do so. A measure of this parameter is

called water activity, denoted by aw.

Water Activity

Water Activity

Water activity is a measure of water available to microorganisms. Pure water has a water activity of 1.0 while most fresh foods have a water activity of about 0.99.

In general bacteria require a higher aw than yeasts and molds. Most spoilage bacteria cannot grow at aw < 0.91, with Clostridium botulinum having a minimum growth level of 0.94. Staphylococcus aureus, has, however, been found to grow at aw as low as 0.84. The lowest reported aw

for bacterial growth is 0.75. Most spoilage molds cannot grow at aw < 0.80. The lowest reported aw for any mold growth is 0.65, and that for yeasts 0.61.

Minimum Water Activities for growth of Different Microorganisms

Normal bacteria 0.91

Normal yeasts 0.88

Normal molds 0.80

Xerophilic molds 0.65

Osmophilic yeasts 0.60

Humidity

The humidity of the environment is important as it affects the aw of the food as well as the moisture content of the food surface. Food can pick up moisture from the atmosphere. Under conditions of high relative humidity storage (e.g., in a refrigerator), surface spoilage can take place, unless food is adequately protected by packaging.

pH

Most microorganisms grow best at neutral pH and only a few are able to grow at a pH lower than 4.0. Bacteria are more fastidious about their pH requirements than yeasts and molds. The fact that pH can limit microbial growth is a basic principle of food preservation and has been exploited for thousands of years. Fermentation and pickling extend the shelf-life of food products by lowering the pH. The fact that no known spore-forming pathogenic bacteria can grow at pH < 4.6 is the basis for the food sterilization principle for low-acid and acid foods.

Oxygen Availability

Controlling the availability of free oxygen is one means of controlling microbial activity in food. Although oxygen is essential for carrying out metabolic activities that support all forms of life, some microorganisms use free atmospheric oxygen, while others metabolize oxygen (reduced form) bound to other compounds such as carbohydrates.

Microorganisms can be broadly classified into two groups: aerobic and anaerobic. Aerobes grow in the presence of atmospheric oxygen, while anaerobes, in the absence of atmospheric oxygen. In between these two extremes are facultative anaerobes, which adapt and grow with or without atmospheric oxygen, and microaerophilicorganisms, which grow in the presence of reduced amounts of atmospheric oxygen.

Oxygen Availability

At the surface and within protein foods, oxygen availability and oxygen tension govern the numbers and type of food-colonizing spoilage microorganisms. The exposed surface of fresh meat and fish have a high oxygen tension and therefore support a large number of aerobic microorganism, such as Pseudomonas spp., Achromobacter spp., bacilli, micrococci, yeasts and fungi.

Osmotic Pressure

Osmotic pressure is inversely related to water activity. As the osmotic pressure of any system increases, water activity decreases. Thus, high osmotic pressures are normally incompatible with living organisms due to the osmotic effects that tend to dehydrate living cells.

Food spoilage associated with protein degradation

Type of food Spoilage

Milk Cogulation of caseins, off-flavors, racidity, putrefaction, cadaverine

Meats Surface slimes, liquefaction, degradation of collagen, elastin, keratin, putrefaction, cadaverine, putrescine

Fish Fishy odor, TMA, DMA, surface slimes, H2S, cadaverine, putrescine, indole

Hams, bacon, chicken, turkey

Greening, putrefaction, liquefaction, bone taint, rancidity

Eggs White, rot, black rot, mixed rot, fungalinfections

Cheese moldy

Food spoilage associated with fats degradation

Food Spoilage

Milk Souring

cream Rancidity, free fatty acid

butter Free fatty acid

Margarine Rancidity, methyl ketones

Oats Bitterness

Wheat Soapiness

Rapeseed oil Lipoxidation

Microbial lipases

• Cleave triglycerides at either• 1,3 position

• 2-position

-oxidation

• Yield keto-acids, methyl ketones, secondary alcohols, shorter fatty acids such as butyric, propionic acid, acetic acid

Acyl CoA dehydrogenase

Enoyl CoA hydratase

-hydroxylCoA dehydrogenase

Thiolase

Pathway for -oxidationOf a Fatty Acid