food deterioration
TRANSCRIPT
BIODETERIORATION
OF FOOD
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.
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.
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
TYPES OF BIODETERIORATION
1. Chemical Biodeterioration
2. Physical Biodeterioration
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.
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.
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.
Chemoheterotophs that can cause food biodeterioration are referred to as biodeteriogens.
They include the following:
1. Bacteria
2. Fungi
3. Insects
4. Higher animals
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.
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.
Factors affecting food spoilage
• Chemical composition of food
• Type of organisms involved
• Environmental conditions of food and microorganisms
• Changes occurring in food
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
• Microbial deterioration of
carbohydrates
• Microbial deterioration of
proteins and protein foods
• Microbial deterioration of
edible oils and fats
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.
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).
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
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.
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
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
• 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
• 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
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
Biodeterioration of Fruit Juices and Fruit Juice Concentrates
• 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.
• 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
1. Slime formation
2. Alcohol fermentation
3. Breakdown of organic acids
to lactic acid
Other Mechanisms of Fruit Juice
Spoilage
• 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
• 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
• 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
• 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
Microbial Spoilage of Beer, Wine and Fermented Beverages
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.
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
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
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.
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
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
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
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
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
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.
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.
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
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.
Microbial Deterioration of Plant Pectin and the Development of Soft
Rot in Fruit and Vegetables
• 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
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.