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

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Presentation on theme: "Food Spoilage and Preservation Professor James Dooley School of Biomedical Sciences, University of Ulster, Coleraine."— Presentation transcript:

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 Food VitaminsProteins Carbohydrate Lipids Human Growth Energy Building materials Microbial 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.

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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

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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 (10-45 o C) psycrophiles (0-20 o C)

25 What do bacteria need to grow? pH 6-7.5 Absence of toxic chemicals Correct atmosphere (O 2 ) Aerobic Bacillus Anaerobic Clostridium facultative anaerobes Salmonella

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

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

30 What happens when bacteria grow in food? Food Components: Starch, protein etc. Waste products: CO 2 Alcohol Lactic acid etc. Altered Environment Altered Food Digestive enzymes Sugars, amino acids 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 121 o C 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 4 o C degrees rate of spoilage decreased storage at -20 o C degrees rate of spoilage extremely slow need -70 o C 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 Co 60 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

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51 A little extra material... BBC Radio 4 Science “On the shelf” http://www.bbc.co.uk/radio4/science/connect_2002103 0.shtml Food Safety Through the Ages Dr. Bill Grierson http://www.acsh.org/healthissues/newsID.767/healthiss ue_detail.asp http://www.acsh.org/healthissues/newsID.767/healthiss ue_detail.asp Food Preservation site Good links to related material http://www.bookrags.com/sciences/biology/food- preservation-wmi.html http://www.bookrags.com/sciences/biology/food- preservation-wmi.html Food Standards Agency www.food.gov.uk/ Good site for general information

52 A little extra material... A good site to visit http://resources.schoolscience.co.uk/SGM/index.html

53 Food preservation challenges

54 Tests for food spoilage EGGS - When something starts pecking its way out of the shell, the egg is probably past its prime. Especially if the something is NOT a chicken. DAIRY PRODUCTS - Milk is spoiled when it starts to look like yogurt. Yogurt is spoiled when it starts to look like cottage cheese. Cottage cheese is spoiled when it starts to look like regular cheese. Regular cheese is nothing but spoiled milk anyway and can't get any more spoiled than it is already. Cheddar cheese is spoiled when you think it is blue cheese but you realize you've never purchased that kind. Blue cheese, by definition, is never spoiled. FROZEN FOODS - Frozen foods that have become an integral part of the defrosting problem in your freezer compartment will probably be spoiled - (or wrecked anyway) by the time you pry them out with a kitchen knife.

55 Tests for food spoilage MEAT - If opening the fridge door causes stray animals to congregate outside your house, the meat is spoiled. BREAD - Sesame seeds and Poppy seeds are the only officially acceptable "spots" that should be seen on the surface of any loaf of bread. Fuzzy and hairy looking white or green growth areas are a good indication that your bread has turned into a pharmaceutical laboratory experiment. FLOUR - Flour is spoiled when it wiggles. SALT - It never spoils. LETTUCE - lettuce is spoiled when you can't get it off the bottom of the fridge without Mr Muscle.

56 Tests for food spoilage CANNED GOODS - Any canned goods that have become the size or shape of a softball should be disposed of. Carefully. CARROTS - A carrot that you can tie in a clove hitch in is not fresh. RAISINS - Raisins should not be harder than your teeth. POTATOES - Fresh potatoes do not have roots, branches, or dense, leafy undergrowth. CHIP DIP - If you can take it out of its container and bounce it on the floor, it has gone bad. GENERAL RULE OF THUMB - Most food cannot be kept longer than the average life span of a hamster. Keep a hamster in or nearby your fridge to gauge this.


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