Food Spoilage and Preservation

1. Food Spoilage and Preservation Professor James Dooley School of Biomedical Sciences, University of Ulster, Coleraine

2. Food Spoilage and Preservation • Essential element of modern society • Not appreciated by most individuals • A changing environment requiring constant innovation • Will always be a problem for humans

3. Hunter-Gatherer society • supported low numbers/ self-sufficient • unreliable food supply • limited specialisation of individuals

4. Industrial and Agricultural society • supports high numbers/ produce excess • supports specialisation • generally predictable food supply

5. Vitamins Proteins Food Energy Building materials Lipids Carbohydrate Microbial Growth Human Growth

6. What are microbes? • “Organisms that are too small to be seen with the naked eye” • Bacteria • Viruses • Fungi • Protozoa

7. What are bacteria? • Unicellular organisms • Very small!!!!!!! • 1-10 microns • Enormous diversity • Shape • Habitat • Nutrition • Many bacteria require similar growth and nutrition conditions to humans • very many do not but we do not deal with them when considering food spoilage and preservation.

8. Light Microscope x 1,000

9. Where do we find bacteria? • Everywhere! • Soil • Plant roots • Water • Bodies of animals, fish, birds etc, • Hot springs • Dead Sea • Hydrothermal vents

10. What are microbes? • “Organisms that are too small to be seen with the naked eye” • Bacteria • Viruses • Fungi • Protozoa

11. General features of Fungi • unicellular (yeasts) and multicellular (moulds) • Non-photosynthetic,plant-like organisms • Multicellular, filamentous organisms • Normally inhabitants of the soil, rhizosphere and water • Can tolerate acidic and dry conditions

12. Fungi in Nature • Metabolic by-products form the raw material for many industries: • ethanol • antibiotics • enzymes (washing powders etc.) • solvents • food flavours • Cholesterol-lowering drugs – mevacor • Fungi are the main organisms involved in the decay of organic material and the recycling of essential elements (C, N, etc.) • Yeast are good model organisms for genetic manipulation.

16. Micro-organisms and food • Agents of food production

17. Micro-organisms and food • Agents of disease

18. Micro-organisms and food • Agents of food spoilage

20. Food Spoilage and How to Prevent it • We need to know about how spoilage organisms live • We need to understand their biology • We need Microbiologists!

21. Laboratory study of bacteria

22. Bacterial growth

23. Doubling is a Big Deal • Some bacteria can double every 30 min. and a few can double in 20 minutes!! • Escherichia coli • 20 minutes • Mycobacterium tuberculosis • 15 hours

24. What do bacteria need to grow? • Source of nutrients • amino acids, sugars, lipids, vitamins • released by action of enzymes operating outside the cell • starch digested by amylase • Correct temperature • Bacteria grow within temperature ranges • mesophiles (10-45oC) • psycrophiles (0-20oC)

25. What do bacteria need to grow? • pH • 6-7.5 • Absence of toxic chemicals • Correct atmosphere (O2) • Aerobic • Bacillus • Anaerobic • Clostridium • facultative anaerobes • Salmonella

27. Super Tough Bacteria! some bacteria produce endospores response to stress very resistant to heat 121oC very resistant to harsh chemicals, drying, radiation can remain dormant for a long time (years) endospore - forming bacteria are common in soil

29. Nutrients Suitable Environment Time More Bacteria! What happens when bacteria grow?

30. Sugars, amino acids etc. Digestive enzymes Altered Environment Altered Food What happens when bacteria grow in food? Food Components: Starch, protein etc. • Waste products: • CO2 • Alcohol • Lactic acid etc.

31. Microbial Food Spoilage • Microbial growth introduces unwanted alterations in food • appearance • smell • Taste • Nutritional content • Changes not necessarily harmful! • Each food unique microbial environment • unique spoilage agents

32. Three groups of foods:based upon rate of spoilage • highly perishable • meat • fruit • milk • vegetables • eggs • semi perishable • potatoes • nuts • stable • rice • flour • dry beans What defines each group? Amount of water WET Dry

33. Food Spoilage • Each food has it’s own unique microbial population • Uncontrolled growth of the microbes results in food spoilage • We can predict (and therefore control) food spoilage

34. Milk spoilage (unpasteurised) • Bacterial growth on milk sugars • (Lactobacillus spp., Lactococcus spp.) • pH reduction • lactic acid build up (bitter taste!) • Change in bacterial population • further pH reductions and much more lactic acid, continues until all sugars depleted • Yeasts and moulds dominate • use lactic acid for growth. • pH rise • allowing further bacterial growth • Bacteria use proteins as major nutrient • (Primary amines produced- Smelly!!!!!)

35. Food spoilage has major economic impacts

36. Microbial food spoilage • Foods are characteristically spoiled by known organisms

37. Food Spoilage Shapes History

38. Nicholas Appert • a Frenchman who invented a method to preserve perishable organic materials. • In 1809, Appert received 12,000 francs for his method of enclosing food in airtight jars which were then heated. • boiling products in jars for four to six hours and then pouring molten wax over the jars.  • By this method, food could be preserved indefinitely. • Unfortunately, the glass jars often broke on their trip to the army!!!!

39. Preservation of food by killing all microbes • Temperature • canning • sterilization by heat • 121oC for 15 minutes • all bacteria and endospores killed

40. Preservation of food by killing all microbes • Removal or killing of all microbes from a food will prevent spoilage! • Removal or killing of all microbes from a food will drastically alter the food • taste • texture • nutritional content

41. Preservation of food by preventing microbial growth • A number of parameters can be manipulated to slow down microbial growth • Moisture content {water activity (Aw)} • Perishable foods have a high Aw • preserve by lowering Aw

42. How to reduce water? • drying • sun • heat • freeze - dried (expensive!)

43. How to reduce water? • addition of salt or sugar • water needed to keep salt and sugar in solution

44. Preservation of food by preventing microbial growth • pH • very few bacteria grow below pH 5.0 • How to make food acidic? • Add acid e.g. acetic acid • Allow bacteria to make acid from natural food components • lactic acid bacteria

45. Preservation of food by preventing microbial growth • Temperature • storage at 4oC degrees • rate of spoilage decreased • storage at -20oC degrees • rate of spoilage extremely slow • need -70oC to eliminate spoilage

46. Preservation of food by preventing microbial growth • Temperature • Pasteurization • mild heat treatment • overall microbial population is reduced • pathogens are eliminated since these tend to be more heat sensitive than other organisms. • 63°C for 30 min. (batch pasteurization) • 72°C for 15 sec. (flash pasteurization)

47. Food Preservation by control of bacterial growth • Radiation • use of gamma rays from Co60 • microbes killed by free radicals • Food can be packaged! • No recontamination possible • Pasteurization of meat, poultry, cheese • No alteration of food • controversial claim

48. Irradiation is controversial • Irradiation of various foods accepted in US and many other countries • UK only allows for irradiation of herbs, spices or vegetable seasonings

49. Preservation of food by preventing microbial growth • Modified Atmosphere Packaging • Oxygen • Nitrogen • Carbon Dioxide • Argon • Mix depends on food in question