Food spoilage

1. Food spoilage What causes it How to minimize it

2. You know it when you see it Or smell it Or taste it Inmagine.com Mahalo.com

3. What are the steps of food spoilage? • Introduce microbes to food • Food environment is favorable for growth • Food is stored at a temperature that favros growth • Enough time elapses • Thermoduric microbes survive heat treatment • Heat-stable enzymes can degrade food • Bacteria, molds, and yeasts cause most food spoilage

4. Microbes and food • Most nonsterile foods contain many types of microbes • Spoiled foods have one or a few- that outgrew the others (much more slowly than in laboratory conditions!) • Aerobic foods: Pseudomonas • Anaerobic foods: Lactobacillus or Leuconostoc

5. Animal muscle tissue contains few bacteria Scienceblogs.com • Hide, hair, hooves, GI tract • Hide removal • Breaching GI tract • Processing environment and tools • Staphylococcus, Micrococcus, Pseudomonas

6. Poultry Goldcoastcommodities.com Skin, feathers, and feet Feces and litter from coops Potable water for chilling

7. Finfish and shellfish Americanvision.org • Water temperature and feeding patterns • Warm vs cold • Psychrotrophic vs mesophilic microbes • Bottom feeders, filter feeders (molluscs) • Harvesting methods • Trawling vs line caught • Storage

8. What kinds of microbes cause meat spoilage? Common bacterial species Mechanisms Adherence (pili) Formation of glycocalyx Motility Adaptation to temperature, pH • Pseudomonas • Acinetobacter • Moraxella • Micrococcus • Staphylococcus • Shewanella in poultry • Fungi • Among others

9. Recall types of microbes Oxygen requirements Temperature optima So different types of microbes can grow as conditions change

10. Growth under storage conditions • Microbes were intrinsic or introduced by processing • Generally few species grow • Aerobic conditions: Pseudomonas favored • Vacuum packed: lactobacilli if low pH • Bacillus and Shewanella can grow at higher pH • Lowering aw reduces microbial growth

11. Meat, poultry, and fish are good food sources for microbes • High aw • Protein > lipids > carbohydrates • Microbial metabolism will lower pH • Slow cooling may favor the growth of anaerobes in deep tissue • Fungi may grow if surface gets dry • Fish vary in lipid content • Molluscs have higher carbohydrate content and are spoiled by fermenters

12. Spoilage factors are diverse like the food environment • Carbohydrates metabolized first, then lipids, then proteins (as microbial count increases) • Products from: • Carbohydrates- carbon dioxide or fermentation products • Lipids- aldehydes, ketones, short-chain fatty acids • Proteins- amino acids, amines, short peptides • Nonprotein nitrogenous compounds (usu. breakdown products from lysed cells)

13. How does microbial metabolism adversely affect food? • Volatile end products produce odor • Oxidation of pigmented products can change color • Breakdown of tissues by degradative enzymes can change texture • Production of dextran or sheer numbers can produce slime • Water can be released (“purge”)

14. Specific spoilage organisms: meats • High protein, low carbohydrate • High aw, pH tends to be acidic • Aerobes: Pseudomonas (grows fast), expends glucose • Acintobacter and Moraxella prefer to utilize amino acids • Facultative anaerobes and anaerobes if oxygen is limited (vacuum-packed meats) • Comminuted (ground) meats spoil faster due to increased surface area

15. Different issues with processed meats Heat-resistant organisms Introduced by handling Preservatives often added Lactobacillus Leuconostoc Amino acid metabolism Putrefaction, odor, sliminess

16. Eggshells do not protect against microbial infection! Eggs do have natural protection lysozyme, alkaline pH, chelators, protease inhibitors Gram-negative motile rods green, black, red rots Dried eggs not susceptible to spoilage

17. Milk and milk products • What’s in milk? • Protein • Casein, lactalbumin, amino acids • Carbohydrate • lactose • Lipids • Degraded by milk lipases into butyric, capric, caproic acids • Minerals

18. Pasteurization does not kill everything • Micrococcus, Enterococcus, and others can survive • Pseudomonas, spore formers, and others can be introduced afterward • UHT (ultra high temperature, 150oC for a few seconds) is essentially sterilized • Concentrated milk products are heat treated • Butter tends to be contaminated by yeasts and molds

19. Fruits and vegetables Vary in carbohydrates, proteins, pH What sorts of organisms would spoil them? Innate or introduced?

20. Fermented foods are not immune to spoilage Generally yeasts and acidophilic bacteria

21. Canned foods Heat treated to kill microbes Low acid: kill most spore formers flat sour- no gas thermophilic anaerobe-gas sulfide stinker- gas and discoloration High acid: all vegetative bacteria

22. Refrigerated foods • Psychrophilic and psychrotrophic microbes • Handling introduces microbes • Some pathogens can grow at low temperatures • With long storage, microbes can increase to disease causing levels • Competitive advantages: adaptation to cold. Low O2, production of bacteriocins • Clostridium grow in vacuum-packed foods

23. Summary • Why are different foods spoiled differently? • Available nutrients • Capability for rapid growth of microbes • End products: organics, inorganics, gases? • Enzyme activity?