food deterioration

49
BIODETERIORATION OF FOOD

Upload: foodbiochemistry

Post on 15-Jul-2015

267 views

Category:

Food


1 download

TRANSCRIPT

Page 1: Food deterioration

BIODETERIORATION

OF FOOD

Page 2: Food deterioration

ALL food undergoes deterioration to some degree once harvested or slaughtered. The deterioration includes loss of nutritional value, organoleptic changes, and most importantly safety may become compromised. It is the challenge of the food industry to control this deterioration and maintain the safety of the food, while making sure that the food is as convenient, nutritious and available as it can possibly be.

Page 3: Food deterioration

FOOD BIODETERIORATION

•Any undesirable change in the property of food caused by the vital activities of organisms.

• It is a result of the metabolic processes of microorganisms acting singly or in groups to break down complex organic substances or of the damage caused by insects, rodents or birds.

In layman’s term, SPOILAGE.

Page 4: Food deterioration

BIODETERIORATION

• Biodeterioration is DIFFERENT from biodegradation, in that the former is

Undesirable Uncontrollable Caused by organisms.

• It is NOT the natural degradation that occurs in some organic materials or food caused by intrinsic enzymes.

• DIFFERENT

Page 5: Food deterioration

TYPES OF BIODETERIORATION

1. Chemical Biodeterioration

2. Physical Biodeterioration

Page 6: Food deterioration

CHEMICAL BIODETERIORATION

1. Biochemical assimilatory biodeterioration

The organism uses the food components for nourishment, i.e., as an energy source.

2. Biochemical dissimilatory biodeterioration

The chemical change in the food is a result of waste products from the organism in question.

NOTE: Both have the same result, i.e., the material becomes spoilt, damaged or unsafe.

Page 7: Food deterioration

PHYSICAL BIODETERIORATION

1. Mechanical biodeterioration

This occurs when the food is physically disrupted/damaged by the growth or activities of the organism.

2. Soiling/fouling

This occurs when the appearance of a product is compromised, BUT it does NOT necessarily makes the product unsafe; it only renders the product unacceptable to consumers.

Page 8: Food deterioration

Living organisms can be divided on the basis of their nutritional requirements into two:

Autotrophic organisms see all inorganic materials as a potential source of nutrients, while heterotrophic organisms can only use organic matter.

Food biodeterioration is generally caused by heterotrophs, specifically chemoheterotrophs.

autotrophs and heterotrophs.

Page 9: Food deterioration

Chemoheterotophs that can cause food biodeterioration are referred to as biodeteriogens.

They include the following:

1. Bacteria

2. Fungi

3. Insects

4. Higher animals

Page 10: Food deterioration

From Man’s earliest history, control of food biodeterioration has long been a concern. Thus, the basic principles for such control that were applied thousands of years ago have remained unchanged.

• If possible, eat food immediately after harvest.

• Physically protect food from pests by storing in sealed containers.

• Preserve by drying, salting or adding spices.

Page 11: Food deterioration

Why do food spoil?

• Food is made up of water, proteins, fats, carbohydrates and a host of vitamins and minerals. These components are hydrolyzed by microorganisms.

• Hydrolysis products impart undesirable odors and flavors

• Bacteria produce toxins, thereby compromising food safety.

Page 12: Food deterioration

Factors affecting food spoilage

• Chemical composition of food

• Type of organisms involved

• Environmental conditions of food and microorganisms

• Changes occurring in food

Page 13: Food deterioration

Mechanisms of food spoilage

• Fermentation

The conversion of carbohydrates into organic acids, alcohol and CO2 by microorganisms under anaerobic condition

• Putrefaction

The breakdown of proteins by microbial enzymes, usually produced by anaerobic spoilage microorganisms

• Lypolysis

The breakdown of fats into glycerol and free fatty acids

Page 14: Food deterioration

• Microbial deterioration of

carbohydrates

• Microbial deterioration of

proteins and protein foods

• Microbial deterioration of

edible oils and fats

Page 15: Food deterioration

CARBOHYDRATES are the most

abundant class of organic compounds on Earth, being the primary constituents of plants and exoskeletons of crustaceans and insects. Therefore, they are virtually an unavoidable element of our daily life, especially considering that it is an ever-present component of our food.

Page 16: Food deterioration

CARBOHYDRATES

• Carbohydrates are organic compounds that contain carbon, oxygen and hydrogen.

• Basic chemical formula Cn(H2O)n], and thus designated as “hydrates of carbon”

• They can be simple sugars or complex molecules. Food carbohydrates include monosaccharides (e.g., glucose), disaccharides (e.g., lactose and sucrose) and polysaccharides (e.g., dextrins, starches, celluloses, pectins).

Page 17: Food deterioration

Types of Carbohydrate Deterioration

1. Preliminary breakdown of polysaccharides by enzymes

2. Fermentation of monosaccharides and disaccharides to pyruvic acid via the EMP pathway

3. Production of microbial polysaccharides or dextrans from disaccharides

4. Production of pectin esterases and polygalacturonidases that degrade pectin

Page 18: Food deterioration

Preliminary breakdown of high-molecular-weight polysaccharides by enzymes

• Yields a mixture of low-molecular-weight sugars, such as oligosaccharides, disaccharides, and monosaccharides

• Example: Degradation of starch by bacterial or fungal amylases

(C6H10O5)n + nH20 → nC6H12O6 (glucose)(C6H10O5)n + n/2 H20 → n/2 C12H22O11 (maltose)

NOTE: Many bacilli, streptomyces, and aspergilli have

extracellular enzymes such as cellulose, amylases and other

glucanohydrolases.

Page 19: Food deterioration

Fermentation of monosaccharides and disaccharides to pyruvic acid by

microorganisms via the Embden-Meyerhof-Parnas Pathway

C6H12O6 + 2 NAD+ + 2 ADP + Pi

2 CH3COCOOH + 2 NADH + 2 ATP + H+

Metabolic fate of pyruvate

• Conversion of pyruvic acid to lactic acid by lactobacilli

• Reductive decarboxylation of pyruvic acid to ethanol by yeasts

Page 20: Food deterioration

LactobacilliCH3COCOOH + NADH + 2 ATP + H+

NAD+ + CH3CHOHCOOH

Yeast

CH3COCOOH + NADH2 CH3CH2OH + CO2 + NAD+

NOTE: Generally, microbial metabolites produced by spoilage organisms (e.g., lactobacilli, acetobacters and yeast) are directly derived from pyruvate.

Pyruvic acid Ethanol

Lactic acid

Pyruvic acid

Page 21: Food deterioration

• Microbial dextrans are polysaccharides in which the a-D-glucopyranose units are linked by a-1-6 glycosidic bonds

• They form unpleasant slimes in and on food, making food unpalatable and unacceptable to consumers.

• Example: Slimy and ropy texture of fruit concentrates infected by L. mesenteroides or B. mesentericus

Production of microbial polysaccharides

or dextrans from disaccharides

Page 22: Food deterioration

• Pectin is a structural heteropolysaccharide in the primary cell walls of terrestrial plants

• Pectin-degrading enzymes cause soft rot.

• Bacillus polymyxa, Erwinia carotovora and Sclerotinia sclerotiorum are associated with soft rot in vegetables, whereas Penicilliumcitrinum, P. digitatum and P. italicum in citrus fruits.

Production of pectin esterases and

polygalacturonidases that rapidly

degrade pectin in fruit and vegetables

Page 23: Food deterioration
Page 24: Food deterioration

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

Page 25: Food deterioration

Biodeterioration of Fruit Juices and Fruit Juice Concentrates

Page 26: Food deterioration

• They readily convert soluble sugars in the

juices to a mixture of lactic acid and acetic

acid.

• They grow at low pHs.

• They metabolize malic acid to lactic acid and

citric acid to succinic acid, resulting in loss of

acidity, equated with blandness, flat taste

and loss of astringency.

Lactobacillus species are the most

common bacteria associated with

fruit juice spoilage.

Page 27: Food deterioration

• Lactobacilli produce lactic acid and

acetic acid as the main metabolites with

the liberation of CO2.

• However, mannitol, diacetyl, acetoin,

ethyl alcohol and succinic acid are also

produced by some strains.

Metabolites

Page 28: Food deterioration

1. Slime formation

2. Alcohol fermentation

3. Breakdown of organic acids

to lactic acid

Other Mechanisms of Fruit Juice

Spoilage

Page 29: Food deterioration

• Leuconostos mesenteroides and

Streptococcus viscosum infection is

associated with slime formation in fruit

juices.

• These organisms produce dextran-type

polysaccharides, giving juice a slimy,

unpleasant texture.

Slime formation

Page 30: Food deterioration

• In fruit juices where the sugar

concentration is very high, 10-30%,

deterioration is mainly caused by

osmophilic yeasts, Saccharomyces

mellis and S. rouxii, which rapidly

ferment the existing sugars to alcohol.

• Candida pulcherrima, C. malicola,

Cryptococcus albidus and several

Torulopsis spp. have also been

isolated from fermenting apple juice.

Alcohol fermentation

Page 31: Food deterioration

• Fruit juices contain organic acids, i.e.,

tartaric, malic and citric acids.

• Although stable to microbial attack,

tartaric acid can be utilized by L.

plantarum to produce lactic acid and by

Bacterium succinicum to produce

succinic acid.

• Malic acid can be converted by other

lactobacilli to lactic acid, and citric acid to

lactic and acetic acids.

Breakdown of organic acids

to lactic acid

Page 32: Food deterioration

• Most fruit juice spoilage organisms are

inhibited below 8˚C; thus, fruit juice and juice

concentrates should be stored at 4˚C.

• At high pH (≥4), infection by butyric acid

bacteria may also occur. Such infection is

due to careless cleansing of the plant and

storage vessels --- detergent, soap and

caustic soda remain, contaminating the juice

and raising its pH, allowing bacteria to

proliferate. Thus, thorough cleansing is

essential.

Prevention of Fruit Juice Spoilage

Page 33: Food deterioration

Microbial Spoilage of Beer, Wine and Fermented Beverages

Page 34: Food deterioration

Acetification or vinegar souring is the most

common spoilage defect in beer, wine and

fermented beverages. Therefore, the culprit

organisms for the aerobic oxidation of ethanol

to acetic acid are acetic acid bacteria, mainly

of the genus Acetobacter.

For example, A. aceti, A. oxydans, A. xylinum,

A. roseum and A. melanogenum have been

isolated from acetified wines.

Whereas, A. turbidans, A. viscosum and A.

capsulatum are responsible for beer spoilage.

Page 35: Food deterioration

1. Dehydrogenation of ethyl alcohol to

acetaldehyde by alcohol dehydrogenase

CH3CH2OH + NAD+ CH3CHO + NADH + H+

2. Dehydrogenation of acetaldehyde to acetic

acid by acetaldehyde dehydrogenase

CH3CHO + H2O + NAD+ CH3COOH +

NADH + H+

NOTE: All alcoholic beverages containing less than

15% ethanol (w/v) are susceptible to acetification.

Acetification Process

Page 36: Food deterioration

Acetobacters also have gluconic oxidase,

which readily oxidizes glucose to gluconic

acid.

C6H12O6 + FAD C6H10O6 + FADH2

C6H10O6 + H2O HOCH2(CHOH)4COOH gluconic acid

gluconolactoneglucose

gluconolactone

gluconic oxidase

Page 37: Food deterioration

Generally, infection by Acetobacter, especially A. aceti, increases the amounts of volatile and fixed free organic acids and decreases the ethanol and glucose contents of alcoholic beverages.

Thus, acetified beer, wine, and cider have a harsh vinegary taste and a cloudy appearance.

Page 38: Food deterioration

Other Spoilage Microorganisms1. Flavobacterium proteus Causes beer brew infection by

fermenting carbohydrates in the wort to give a mixture of

ethanol and acetic acid, conferring a parsnip flavor to beer.

2. Lactobacillus pasteurianus, Pediococcus damnosus, and P.

perniciosus Produce lactic acid and dextran haze in beer,

imparting a sweet-sour flavor.

3. Brettanomyces bruxellensis and B. schanderlii Start

secondary fermentation giving beer bitter and off flavors.

4. Candida mycoderma, C. krusei and Pichia

membranaefaciens Produce dextran haze, films, off flavors

and off odors in the finished products

5. Leuconostoc, Streptococcus and some Acetobacter species

Produce dextran slimes

6. Micrococcus species Ferment malic acid to lactic acid

7. Pediococcus strains Produce only lactic acid from glucose

Page 39: Food deterioration

1. Acidity and pH

2. Sugar content

3. Alcohol concentration

4. Presence of vitamins and amino acids

5. Tannin concentration

6. SO2 Concentration of

7. Storage temperature

8. Presence or absence of air

Factors governing wine biodeterioration

Page 40: Food deterioration

The relatively low pH and high alcohol content

of most wines and all spirits are sufficient to

prevent microbial growth, especially

pathogenic ones.

Generally, the lower the pH and the higher the

alcohol content, the more stable and resistant

to spoilage is the alcoholic beverage.

Acidity and pH

Page 41: Food deterioration

Sweet wines (1% sugar) are very

susceptible to microbial spoilage. This is

equally true for home-brewed fruit

wines, which have a high sugar content

of up to 5%. Dry wines (0.1% sugar) are

resistant.

Sugar content

Page 42: Food deterioration

Different microorganisms have different

tolerances to alcohol:

Acetobacter 8-10

Micrococcus 8.5-11

Leuconostoc 10-11

Lactobacillus 15-20

Generally, an alcohol content of 8-10%

inhibits microbial growth.

Alcohol concentration

Page 43: Food deterioration

Vitamins and amino acids

The presence of vitamins and amino

acids – added in the form of yeast and

malt extracts – facilitates the growth

of microorganisms.

Page 44: Food deterioration

Tannin concentration

Tannins have an inhibitory effect on

most spoilage organisms. However,

it is normally necessary to keep

their concentration as low as

possible as they impart a bitter

taste to the drink, making it

unpalatable.

Page 45: Food deterioration

Storage Temperature

Most beer, wine and cider are best

stored in a cool cellar or cold storage,

since most microorganisms are

inhibited below 8˚C

Lactobacilli prefer a warm

environment:

Lactobacillus spp. 30-35˚C

Leuconostoc spp. 20-30˚C

Page 46: Food deterioration

Presence or Absence of Air

In bottling beer, wine and fermented

beverages, it is important that the

anaerobic condition is maintained;

thus, bottling under nitrogen or carbon

dioxide, or complete filling without a

headspace is practiced to exclude

oxygen in order to prevent aerobic

acetobacters from flourishing.

Page 47: Food deterioration

Microbial Deterioration of Plant Pectin and the Development of Soft

Rot in Fruit and Vegetables

Page 48: Food deterioration

• 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, the galacturonic

acid residues are linked by a-1-4 glycosidic

bonds and the carboxyl groups are esterified

to methanol in a random manner

Page 49: Food deterioration

Types of Pectic Substances1. 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 methoxyl groups, 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 form gels with sugars and water

4. Pectins Water-soluble pectinic acids containing about 6-7% methoxyl, which forms gels with sugars and acids.