FOOD SPOILAGE

FOOD SPOILAGE

1. WELCOME

2. FOOD SPOILAGE

3. Food spoilage means the original nutritional value, texture , flavor of the food are damaged, the food become harmful to people and unsuitable to eat.

4. 4

5. • Food spoilage can be the result of: – Insect damage – physical injury – E nzymatic degradation – Microbial activity 5

6. Main causes of food spoilage Physical changes aw , temperature, mechanical effects Caused by the inappropriate transport, handling and storage Biological factors Microbiological B acteria , yeasts, moulds (most common) Microbiological Rodents , insects, birds, parasites Chemical , biochemical factors N on-microbial or enzymatic changes usually involving oxygen ® oxidation processes (e.g., rancidity of fats and oils) A ctivity of endogenous tissue enzymes (food of vegetable or animal origin) 6

7. Effects of food spoilage Changes in nutritional value Decomposition of proteins , carbohydrates, vitamins Changes in organoleptic features Colour , flavour , taste, unpleasant odour. U nwholesome effects Biogenic amines, toxins, Metabolites of microorganisms Pathogen microbes 7

8. Spoilage Signs • Odor : – Breakdown of proteins (putrefaction) e.g. “rotten egg” smell • S liminess - Primarily due to surface accumulation of microbial cells and also be a manifestation of tissue degradation • Discoloration – Mould on bread, blue and green mould on citrus fruit and cheese 8

9. • Souring – Production of acid e.g. sour milk from production of lactic acid • Gas formation – Meat becomes spongy – Swollen or bubbling packages and cans 9

10. 10

11. Two types of Spoilage: • Microbial spoilage • Non- Microbial Based on rate of spoilage: • Highly perishable – Meat, fish, poultry, eggs, milk, most fruits and vegetables . • Semi perishable – Potatoes, some apple varieties, nutmeats • Stable or non-perishable – Sugar, flour, dry beans 11

12. a . Physical spoilage • moisture loss or gain 12

13. b . Chemical spoilage • Oxidation of fat • Browning of fruits and vegetables 13

14. c. Microbial spoilage • Growth of microorganisms • Enzyme production 14

15. Microbial spoilage of food • Bacteria, yeasts and moulds are the major causes of food spoilage. • They produce various enzymes that decompose the various constituents of food. • Moulds are the major causes of spoilage of foods with reduced water activity. e.g dry cereals and cereal product • Bacteria spoil foods with relatively high water activity such as milk and products. 15

16. Sources of microorganisms in food The primary sources of microorganisms in food include: 1. Soil and water 2. Plant and plant products 3. Food utensils 4. Intestinal tract of man and animals 5. Food handlers 6. Animal hides and skins 7. Air and dust 16

17. Factors affecting microbial growth ( a) Intrinsic factors: These are inherent in the food. They include: Hydrogen ion concentration (pH), M oisture content, N utrient content of the food, A ntimicrobial substances ad B iological structures. 17

18. (b). Extrinsic factors • Are factors external to the food that affect microbial growth. They include: 1 . Temperature of storage, 2 . Presence and concentration of gases in the environment 3 . Relative humidity of food storage environment . 18

19. Microbial spoilage – how does it manifest itself? Visible growth Gas production Slime Off-flavours 19

20. 20

21. Sequence of events in food spoilage Microorganisms have to get into the food from a source ↓ Food environment should favour the growth of microbes ↓ Food need to be stored under the growth condition for a sufficient length of time • To allow sufficient number necessary to cause spoilage or changes in food. • To allow the produced enzyme to spoil the food. 21

22. SPOILAGE OF CEREALS • Moisture content above 12 to 13 percent may cause spoilage of cereals • Little moisture cause mould growth and high moisture may cause growth of yeasts and bacteria. • Microbial content, physical damage and temperature are also some factors. • Aspergillus , Penicillium , Mucor , Rhizopus , Fusarium are some common moulds ; produce mycotoxins . • Acetobacter spp , lactics and Coliforms, Micrococci and Bacillus are some species causing spoilage.

23. SPOILAGE OF MILK • An excellent medium • Souring – caused by Streptococcus lactis , Enterococci . • Gas production – caused by Coliform, Clostridium, Yeasts . • Proteolysis – c ause bitter taste, caused by Bacillus , Micrococcus. • Changes in colour and tastes 24

24. 25

25. SPOILAGE OF MEAT • Raw meat is subject to spoilage by its own enzymes and microbial action. • Excessive autolysis can cause souring • Factors involving spoilage include – The greater gut load of animal – The physiological condition of the animal during slaughter as like fever, excited or fatigued. – Rapid cooling 26

26. 27

27. SPOILAGE OF FISH • Spoiled by autolysis, oxidation or bacterial activity. • Under aerobic conditions Change in colour of meat pigments • Red colour, green , brown or grey. Off odours and Off tastes 28

28. 29

29. SPOILAGE OF EGGS • Cracks, leaks, stained or dirty spots on exterior and blood clots, bloodiness, translucent spots in the interior are all signs of spoilage • Pseudomonas, certain coliform bacteria. Proteus spp, Aeromonas , Serratia, Sporotrichum all cause rots in eggs. 30

30. 31

31. SPOILAGE OF CANNED FOODS • Chemical spoilage – Hydrogen swell – Discolouration of inside of the can – Cloudiness of liquors – Loss in nutritive value • Biological spoilage – Attacked by • Thermophilic and • Mesophilic bacteria 32

32. 33

33. Vegetables • Vegetables are a good substrate for yeasts, moulds or bacteria • It is estimated that 20% of all harvested fruits and vegetables for humans are lost to spoilage by these microorganisms. 34

34. Soft rot a. One of the most common types of bacterial spoilage. b. caused by Erwinia carotovora • Softening can also be caused by endogenous enzymes 35

35. Mould spoilage a . In vegetables where bacterial growth is not favored , moulds are the principal spoilage agents. b . Most moulds must invade plant tissue through a surface wound such as a bruise or crack. 36

36. Fruits • Like vegetables, fruits are nutrient rich substrates but the pH of fruits does not favor bacterial growth . As a result, yeasts and moulds are more important than bacteria in the spoilage of fruits. 37

37. Fermented products B eer • Spoilage in packaged beer is often due to growth of the yeast Saccharomyces diastaticus , which grows on dextrins that brewers yeast cannot utilize. • In either case, spoilage by yeasts results in the development of turbidity, off flavors and odors . 39

38. 40

39. Wines • Candida valida is the most important spoilage yeast in wine This reduces the acidity of the wine and adversely affect wine flavor . 41

40. SPOILAGE CAN LEAD TO… Food Poisoning • When someone gets sick from eating food or drink that has gone bad or is contaminated. • There are two kinds of food poisoning: poisoning by toxic agent or by communicable agent. 42

41. FOOD PRESERVATION • Food preservation is the process of treating and handling food ,with an aim to stop or slow down its spoilage while maintaining its nutritional value , texture, and flavour. • Food preservation methods either kill microbes or prevent their growth. 43

42. Food preservation principles • Two general principles are employed in food preservation. (1). Inhibition principle ( 2). Killing principle 44

43. (1). Inhibition principle • In this principle, food preservation is achieved by inhibition of growth and multiplication of microorganisms. 45

44. (2). Killing principle • In this principle, spoilage microorganisms are destroyed (Killed) in the food, and the food protected against subsequent contamination by being enclosed in an air tight container. 46

45. Some methods are: 1. Boiling 2. Dehydration 3. Refrigeration & freezing 4. Canning 5. Using chemical preservatives 6. Using Salt, sugar, oil, or vinegar 7. Pasteurization 47

46. How to reduce food spoilage Remove expired or spoiled food Store food in the right parts of your refrigerator Prevent mould growth in the refrigerator Keep some foods separate to prevent spoilage 48

47. 49