MICROBIAL FOOD SPOILAGE

1. MICROBIAL FOOD SPOILAGE Dr. Ir. Eni Harmayani, M.Sc.

2. Important Factors in Microbial Food Spoilage

3. Significance of Microbial Types • Raw and most processed foods normally contain many types of • bacteria (the first important component in spoilage due to a shorter generation time), • yeasts (favorable positions over molds to cause rapid spoilage of foods), • molds, capable of multiplying and causing spoilage. • However, in food where bacteria and yeasts do not grow favorably and the foods are stored for a relatively longer period of time (breads, hard cheese, fermented dry sausages, and acidic fruits and vegetables) spoilage due to mold growth is more prevalent.

4. Significance of Microbial Numbers • The spoilage detection level can range from 106 – 108 cells/g, mL or square centimeter. • Spoilage associated with H2S, some amines, and H2O2 formation can be detected at a lower microbial load, while formation of lactic acid may be detected at a higher microbial load.

5. Significance of Predominant Microorganisms • The microbial profile of a food is quite different from that of a pure culture growing in a laboratory medium. • An unspoiled, nonsterile food generally contains many types of microorganisms consisting of bacteria, yeasts, and molds (also viruses) from different genera and may be more than one species from the same genus. • When the same food is spoiled, it is found to contain predominantly one or two types, and they may not even be present initially in the highest numbers in the unspoiled product.

6. Some Important Food Spoilage Bacteria • Psychrotrophic Bacteria • Aerobic : Pseudomonas fluorescens, P. fragi, other Pseudomonas species, Acinobacter, Moraxella, and Flavobacterium. (some molds and yeasts) • Facultative anaerobic : L. viidescens, L. sake, L. curvatus, Leuconostoc mesenteroides etc. • Thermoduric psychrotrops : • Facultative anaerobs : spores of Bacillus coagulans and Bacillus megaterium, some strains of L. viridescens. • Anerobes : spores of Clostridium laramie, Clo. estertheticum, Clo. algidicarnis, Clo.putrefaciens, and unidentified Clostridium spp. • When a food is temperature abused above 50C, some true mesophiles (growth temperature range 15 – 45 0C, optimum 25 – 40 0C) can also grow. • However, at 10 – 15 0C storage temperature psychrotrophs will generally grow much faster than these mesophiles.

7. Thermophilic Bacteria • The bacteria in this group grow between 40 – 90 0C, with optimum growth at 55 – 65 0C. • Spores of some thermophilic Bacillus and Clostridium spp. can be present in these heat treated foods, which at warm temperatures germinate and multiply to cause spoilage. • Some thermoduric vegetative bacteria surviving low heat processing (such as pasteurization) or thermophiles getting in food as post-heat contamination can also multiply in this warm foods, especially if the temperature is close to 50 0C.

8. Aciduric Bacteria • Bacteria capable of growing relatively rapidly in food at pH 4.6 or below are generally regarded as aciduric (or acidophilic). • Spoilage of acidic food products : • Fruit juices, pickles, salsa, salad dressings, mayonnaise, and fermented sausages. • Heterofermentative LAB and homofermentative LAB have been associated with such spoilage. • Yeast and molds are aciduric and thus are associated with spoilage of such foods.

9. Food Types • Intrinsic factors that can cause food spoilage : • Aw & pH : food with a lower Aw (0.90) or a lower pH (5.3) is less susceptible to bacterial spoilage than one with Aw = 0.98 or pH = 6.4. Yeast and molds will probably grow equally well under both conditions. • O – R potential, nutrient content, antimicrobial substances, protective structures. • Extrinsic factors : storage conditions

11. Metabolism of Food Nutrients

12. Preference for Utilization of Food Nutrients • In general, microorganisms prefer to use carbohydrate first, followed by NPN and proteinaceous compounds, and then lipids. • It again depends on whether or not a particular species has the ability to use specific carbohydrate. • In mixed microbial population, as normally present in food, availability and amount of metabolizable carbohydrates greatly affect the spoilage pattern.

13. Microbial Growth in Succesion • The intrinsic factors or environments of a food dictate which, among the mixed microbial species normally present, will multiply rapidly and become predominant to cause spoilage. • If sufficient time is given, the predominant microbial types and the nature spoilage of a food can change.

14. Spoilage of Specific Food Groups

16. Prevention of spoilage • Knowing types of microorganisms associated with spoilage of specific foods is essential for developing preventive measures • Intrinsic and extrinsic factors can be manipulated to prevent microbial growth

17. Fresh and Ready to Eat Meat Products • Raw Meat • From animals and birds contain a large group of spoilage bacteria • The predominant spoilage flora in a meat is determined by : • the nutrient and oxygen availability, • storage temperature, • pH, • the storage time of the product • generation time of the spoilage microorganisms under a given environment.

18. Meat are more perishable than other food commodities • Abundance all nutrients required for growth of bacteria, yeasts and molds • All of these nutrients readily available • Carcasses and cuts may be spoiled by bacteria or by molds • Whiskers (Mucor, Rhizopus), black or green spots (Cladosporium, Penicillium) • Ground meats and steaks are almost exclusively spoiled by bacteria • Storage temperature selects for psychrotropic spoilage organisms • Pseudomonas, Moraxella, Acinetobacter, Psychrobacter • Steaks tend to undergo surface spoilage

19. Ready to Eat Meat Products • High heat processed uncured and cured meat products (heat treatment to make them commercially sterile) • Low heat processed uncured and cured meat products • Sources of microorganisms : • Raw meat • Spices and other ingredients • Natural casings

20. Spoilage in ready to eat meat products : • Slimy spoilage • Occurs on the outside of casing • Yeast, LAB, B. thermosphacta • Souring • Occurs underneath the casing • Due to growth of LAB • Greening • Due to H2O2 production (Lactobacillus) • Due to H2S production • Reacts with myoglobin to form sulphmyoglobin • Pseudomonas mephitica

21. Eggs and Egg Products • Rotting • Green rots (Pseudomonas fluorescens) • Colorless rots (Pseudomonas, Acinetobacter) • Black rots (Proteus) • Pink rots (Pseudomonas) • Red rots (Serratia) • Custard rots (Proteus vulgaris, P. intermedium) • Pinspots (molds, Penicillium, Cladosporium, Mustiness, P. graveolans, Proteus)

22. Hen’s egg structure includes barriers against microbial entry and growth : • External • Outer waxy shell membrane • Shell • Inner shell membrane • Internal (white) • Lysozyme • Avidin (chelates biotin) • High pH (~ 9.3) • Conalbumen (chelates iron) • Yolk is an excellent medium for bacterial growth

23. Milk and Milk Products • Raw Milk • Microbiota of milk from healty cows • Micrococcus, Staphylococcus, Lactic acid cocci (Lactococcus and Streptococcus) • Microbiota of milk from cows with mastitis • Staphylococcus aureus, Streptococcus agalactiae, Coliforms, Pseudomonas, and other streptococci • Count > 103 in the bulk tank (if not separated) • Spoilage of refrigerated milk consists usually of bitter, rancid, fruity flavors due to putrefaction and caused by psychrotrophs • Spoilage of milk at room consists usually of souring due to fermentation and LAB

24. Pasturized Milk • Usually associated with Gram-negative psychrotrophs • Bitter, rancid, fruity, or unclean flavor • Gram-positive, psychrotrophic sporeformers (Bacillus spp.), can grow and cause spoilage (sweet curdling)

25. Vegetables and Fruits • Widely varied products (raw, frozen, canned, dehydrated, fermented) • Sources of m.o in fresh vegetables and fruits • Soil (Bacillus, Clostridium, fungi) • Wide distribution in nature (Lactobacillus, Leuconostoc, Streptococcus) • Fertilizers (non-fermented manure) • Water (irigation, solvent, washing) • Dust (air) • Animals, insects, humans • Harvesting equipment and utensils • Packing equipment • Ice, transporting vehicles, inadequate storages, cross contamination, handling previous to consumption

26. Types of spoilage on vegetables and fruits Bacterial soft rot Soft, mushy product, sometimes with off-odors Souring by LAB Gray mold rot (Botrytis sp.), Rhizopus soft rot (Rhizopus sp.) and many other rots caused by species of molds Bacteria are of less impotance in the spoilage of fruits because of the lower pH

27. Fish, Crustaceans, and Mollusks • Fish • Microbial spoilage is determined by the microbial types, their level, fish environment, fish types, methods used for harvest, and subsequent handling • Crustaceans • Microbial spoilage in shrimp is more prevalent than that of crabs and lobsters because crabs and lobsters remain alive until they are pocessed • Mollusks • As compared to fish and crustaceans, oyster, clam, and scallop meats are lower in NPN compounds but higher in carbohydrates • The mollusks are kept alive until processed; thus, microbial food spoilage occurs only after processing

28. Soft Drink, Fruit Juices and Preserves, and Vegetable Juices • Among the microorganisms that can be present in these products, only aciduric molds, yeasts, and bacteria (Lactobacillus, Leuconostoc, and Acetobacter) are able to cause spoilage if appropriate preservation methods are not used • To prevent of these potential spoilage microorganisms, several additional preservation methods are used, include : • heat treatment, to kill vegetative microorganisms in tomato juices, • freezing, • refrigeration, • addition of specific chemical preservatives.

29. (Harmayani & Sumedi, 2006)

30. Cereals and Their Products • Cereal grains • If the Aw increase above 0.6, some species of fungi (Aspergillus, Penicillium, and Rhizopus) can grow and cause spoilage • Yeats are common on all cereals, although they represent only a minority of the microbial flora • Refrigerated Dough (biscuits, roles, and pizza) • Susceptible to spoilage (gas formation) from the growth of psychrotrophic heterolactic species of Lactobacillus and Leuconostoc then the gas can blow the containers, especially when the storage temperature increases to 100C or above • Breads • A specific type of bread spoilage, designated as ropiness and characterized by soft, stringy, brown mass with fruity odor, caused by the growth of some mucoid variants of Bacillus subtilis

31. Pastas • Anaerobic packing and refrigeration storage can prevent mold growth and slow down the growth of yeasts, anaerobic and facultative anaerobic psychrotrophic bacteria • Pastries • They can spoilage by microorganisms coming with the ingredients that are added after baking such as icing, nuts, toppings, and cream • Due to low Aw, most products will allow only molds to grow

32. Liquid Sweeteners and Confectioneries • Most of these products have an Aw of 0.8 or below and are normally not susceptible to bacterial spoilage. • Under aerobic conditions, some xerophilic molds can produce visible spoilage • Osmophilic yeasts Zygosaccharomyces rouxii, Saccharomyces cerevisiae, Torulopsis holmii, and Candida valida can ferment these products

33. Mayonnaise, Salad Dressing, and Condiments • Zygosaccharomyces bailii • Lactobacillus fructivorans • Bacillus vulgatus (Thousand Island dressing)

34. Canned Foods • Thermophilic sporeformers • Can cause some types of spoilage of low acid (high pH) foods (such as corn, beans, peas) when the cans are temperature abused at 430C and above, even for short duration • Spoilage due to insufficients heating • Clostridium and some Bacillus spp. • Spoilage due to container leakage • Damage and leakly containers will allow different types of microorganisms to get inside from the environment after heating

35. Fermented Foods • Fermented meat products • If the acid production of homofermentative LAB is slow, undesirable bacteria can grow (Clostridium, Bacillus, and other mesophilic bacteria have been reported to cause spoilage in such conditions. • Products with pH < 5.0 but Aw 0.92 or above and vacuum packaged can be spoiled by heterofermentative Leuconostoc and Lactobacillus spp. with accumulation of gas and liquid inside the package and creamy white growth of bacterial cells • If they are not vacuum packaged and have low Aw (0.72-0.90), yeast and molds can grow on the surface, resulting in slime formation, discoloration, and undesirable flavor of the products.

36. Yeast In Specific Types of Foods • Yeast will actually grow to the extent that spoilage will result depends on intrinsic and extrinsic factors • Many yeast species are associated with plant and animal products and can also be found in food-processing environments • Yeast are most likely to cause spoilage in products such as fruits and soft drinks, which contain fermentable sugars, and in those types of food, e.g., alcoholic beverages and high-sugar and/or high-acidity products, which restrict the growth of competing bacteria

37. Food fermented with mixed cultures of bacteria and fungi (Deak dan Beuchat, 1996)

38. Pustaka : • Deak, T. dan Beuchat, L.R. 1996. Handbook of Food Spoilage Yeast. CRC Press, New York. • Ray, B. 1996. Fundamental Food Microbiology. CRC Press, New York. • Nickerson, J.T. dan Sinskey, A.J. 1974. Microbiology of Food and Food Processing. American Elsevier Publishing Co., Inc.