Food deterioration

Food deterioration

1. BIODETERIORATION OF FOOD

2. 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.

3. FOOD BIODETERIORATION A ny 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 ter m , SPOILAGE.

4. BIODETERIORATION Biodeterioration is DIFFERENT from biodegradation, in that the former is Undesirable Uncontrollable Caused by organisms. I t is NOT the natural degradation that occurs in some organic materials or food caused by intrinsic enzymes. DIFFERENT

5. TYPES OF BIODETERIORATION 1. Chemical Biodeterioration 2. Physical Biodeterioration

6. 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.

7. PHYSICAL BIODETERIORATION 1. Mechanical biodeterioration T his occurs when the food is physically disrupted/damaged by the growth or activities of the organism. 2. Soiling/fouling T his 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.

8. 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 b iodeterioration is generally caused by heterotrophs, specifically chemoheterotrophs . autotrophs and heterotrophs .

9. C hemoheterotophs that can cause food biodeterioration are referred to as biodeteriogens . They include the following: 1. Bacteria 2. Fungi 3. Insects 4. Higher animals

10. From Man’s earliest history, c ontrol 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.

11. 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.

12. Factors affecting food spoilage Chemical composition of food Type of organisms involved Environmental conditions of food and microorganisms Changes occurring in food

13. Mechanisms of food spoilage Fermentation The conversion of carbohydrates into organic acids, alcohol and CO 2 by microorganisms under anaerobic condition Putrefaction T he breakdown of proteins by microbial enzymes, usually produced by anaerobic spoilage microorganisms Lypolysis The breakdown of fats into glycerol and free fatty acids

14. Microbial deterioration of carbohydrates Microbial deterioration of proteins and protein foods Microbial deterioration of edible oils and fats

15. 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.

16. CARBOHYDRATES Carbohydrates are organic compounds that contain carbon, oxygen and hydrogen. Basic chemical formula Cn (H 2 O)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 ).

17. 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

18. 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 (C 6 H 10 O 5 )n + nH 2 0 → nC 6 H 12 O 6 (glucose ) (C 6 H 10 O 5 )n + n/ 2 H 2 0 → n/ 2 C 12 H 22 O 11 (maltose ) NOTE: Many bacilli, streptomyces , and aspergilli have extracellular enzymes such as cellulose, amylases and other glucanohydrolases .

19. Fermentation of monosaccharides and disaccharides to pyruvic acid by microorganisms via the Embden -Meyerhof- Parnas Pathway C 6 H 12 O 6 + 2 NAD + + 2 ADP + P i  2 CH 3 COCOOH + 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

20. Lactobacilli CH 3 COCOOH + NADH + 2 ATP + H +  NAD + + CH 3 CHOHCOOH Yeast CH 3 COCOOH + NADH 2  CH 3 CH 2 OH + CO 2 + 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

21. 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

22. 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 Penicillium citrinum , P. digitatum and P. italicum in citrus fruits. Production of pectin esterases and polygalacturonidases that rapidly degrade pectin in fruit and vegetables

23. 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 v egetables 4. Microbial spoilage of milk 5. Microbial spoilage of raw sugar and sugar confectionery

24. Biodeterioration of Fruit Juices and Fruit Juice Concentrates

25. 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.

26. Lactobacilli produce lactic acid and acetic acid as the main metabolites with the liberation of CO 2 . However, mannitol , diacetyl , acetoin , ethyl alcohol and succinic acid are also produced by some strains. Metabolites

27. Slime formation Alcohol fermentation 3. Breakdown of organic acids to lactic acid Other Mechanisms of Fruit Juice Spoilage

28. 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

29. 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

30. 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

31. 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

32. Microbial Spoilage of Beer, Wine and Fermented B everages

33. 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.

34. 1. Dehydrogenation of ethyl alcohol to acetaldehyde by alcohol dehydrogenase CH 3 CH 2 OH + NAD +  CH 3 CHO + NADH + H + 2. Dehydrogenation of acetaldehyde to acetic acid by acetaldehyde dehydrogenase CH 3 CHO + H 2 O + NAD +  CH 3 COOH + NADH + H + NOTE: All alcoholic beverages containing less than 15% ethanol (w/v) are susceptible to acetification . Acetification Process

35. Acetobacters also have gluconic oxidase, which readily oxidizes glucose to g luconic acid. C 6 H 12 O 6 + FAD  C 6 H 10 O 6 + FADH 2 C 6 H 10 O 6 + H 2 O  HOCH 2 (CHOH) 4 COOH g luconic acid gluconolactone glucose gluconolactone g luconic oxidase

36. 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 .

37. Other Spoilage Microorganisms 1. 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

38. Acidity and pH Sugar content Alcohol concentration Presence of vitamins and amino acids Tannin concentration SO 2 Concentration of Storage temperature Presence or absence of air Factors governing wine biodeterioration

39. 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

40. 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

41. 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

42. V itamins and amino acids The presence of vitamins and amino acids – added in the form of yeast and malt extracts – facilitates the growth of microorganisms.

43. 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.

44. 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

45. 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.

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

47. 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

48. 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 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.