INTRODUCTION TO FOOD MICROBIOLOGY 1105

1. INTRODUCTION TO FOOD MICROBIOLOGY1105 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

2. Introduction to FoodMicrobiology • This module covers the fundamental aspects of bacteria in food starting with the history, what they are and how they grow, classification systems and types of bacteria found in foods. • It focuses primarily on bacteria responsible for food spoilage. Pathogens, bacteria that cause food poisoning, are discussed more extensively in another module (Introduction to Foodborne Pathogens; 1120).

3. Introduction • Microbiology is the study of living forms so small that they can only be seen with the aid of a microscope. • They have been referred to as germs, microbes, bacteria and microorganisms.

4. Photo courtesy of USDA

5. Photo courtesy of USDA

6. Photo courtesy of USDA

7. History • In the early 1700s Leeuwenhoek, the inventor of the microscope was first to observe these microscopic living forms. He referred to them as “wee beasties”. • In 1810, Nicholas Appert, a French confectioner, place food in glass jars, sealed them and heated them in boiling water. He did not know at the time that we was killing spoilage bacteria and invented what is known today as “canning”.

8. History • In the 1860s, Louis Pasteur showed that certain microorganisms were responsible for fermentation and decay. He developed the application of heat to reduce the number of bacteria which now bears his name (e.g. Pasteurization). • In 1895, the Massachusetts Institute of Technology determined that mysterious spoilage of some canned foods resulted from the failure to apply sufficient heat to destroy microorganisms.

9. Biodegradable • Food is “biodegradable” meaning it is degraded back into nature often referred to as “spoilage”. • Microorganisms cause this transition. • The environment is filled with microorganisms-the air we breathe, the soil, it’s everywhere including in our food. • It is our job as food professionals to control these microorganisms before they destroy our food.

10. Microorganisms • There are hundreds of types of microorganisms; *Some cause food spoilage *Some do absolutely nothing *Some are beneficial *Some cause foodborne illness

11. Beneficial Microorganisms • Used to make fermented foods and beverages such as beer, wine, sauerkraut, breads, cheeses, pepperoni and other fermented products. • Antibiotics-penicillin from mold • Enzymes • Fermentation in ruminants.

12. Pathogens • Pathogens are those bacteria that cause foodborne illness. • Although there are hundreds of species of pathogens, the vast majority of foodborne illnesses are caused by just 4 bacteria *Salmonella sp *Campylobacter *Staphylococcus aureus *Clostridium perfringens

13. Bacteria • Although yeasts, molds and bacteria make up the category of microorganisms, we will not be discussing yeasts and mold to any great extent in this module. • We will focus primarily on bacteria since they are the main cause of food spoilage.

14. Bacteria • Bacteria are most important and troublesome for the food processor. • Most bacteria are harmless in themselves but produce excretions and enzymes that result in food spoilage. • They are single-celled living bodies that are 1/1,000 to 1/25,000 of an inch in length. • The number of these tiny organisms that could be placed on the head of a pin would equal the population of New York City.

15. Bacterial Growth • Bacterial growth refers with the way bacteria increase in number. They divide themselves such that 1 bacteria will produce 2 and 2 become 4 and 4 become 8. This doesn’t sound too drastic until you realize that there can be several thousand bacteria per gram of food and they double every so often depending on the environment they are in. • Under optimum conditions, bacteria can double every 20-30 minutes.

16. BACTERIAL GROWTH • Food is generally considered spoiled when the bacterial counts exceed 10 6or 107. This is 1,000,000 to 10,000,000 bacteria per gram. • Most spoilage is a surface phenomenon occurring only on the surface of food unless the food is ground or mixed such as sausage where spoilage occurs on the inside. • Bacterial slime is generally on the order of 108.

17. Bacterial Classifications • Bacteria can be classified in a number of ways. *Their shape-Round=cocci Elongated=rods *Sporeforming; Some rod shaped bacteria are sporeformers. This is a dormant stage in their life cycle. These spores have the ability to survive a wide range of environmental extremes. They can survive heating up to 212F and are resistant to most chemicals including sanitizing solutions. The most noteworthy sporeformer is Clostridium Botulinum.

18. Bacterial Classifications *Based on oxygen requirements; Aerobic-Need oxygen to grow Anaerobic-Can grow only if oxygen is absent Facultative-Can grow with or without oxygen.

19. Bacterial Classifications • Based on optimum temperature for growth; *Psychro=cold *Meso = middle *Thermo= warm *Trophic =growing *Duric=withstand *Phil or philic-prefers

20. Bacterial Classifications • Psychrotropic-grow best at 58-68F but can grow slowly at refrigeration temperatures (32-50F). • Mesophilic-Grows best at 86-98F . Most food spoilage bacteria grow very well at these temperatures. • Thermophilic-Grow best at 100-150F. Most sporeformers fit in this group.

21. CONDITIONS AFFECTING BACTERIAL GROWTH

22. CONDITIONS AFFECTING BACTERIAL GROWTH • There are 6 conditions affecting bacterial growth and can be remembered by the anagram FAT TOM. Food Acidity Time Temperature Oxygen Moisture

23. Conditions Affecting Bacterial Growth FOOD • Bacteria need food to reproduce. • High protein foods and moist starchy foods promote bacterial growth but any food can be potentially risky is not handled properly.

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25. Conditions Affecting Bacterial Growth ACIDITY • pH-measure of acidity or alkalinity. (pH =7 is neutral; 1=acid; 14=basic). • Most bacteria prefer a pH of 5.5-7.5. • Most bacteria, especially pathogens, will not grow at a pH of 4.6 or less (acid). This is why fermented foods such as sauerkraut (fermented cabbage) and fermented sausages were historically used in Europe.

26. Bacteria Molds Yeasts Salmonella Clostridium Botulium Clostridium perfringens Listeria monocytogenes Campylobacter pH Range 0.5-11 1.5-8.5 4.5-9.5 4.8-8.3 5.0-8.5 4.6-9.6 5.0-9.0 pH RANGES OF BACTERIA

27. Food Meat Chicken Fish Fruit Apples Grapes Vegetables Carrot Corn Dairy Milk Cheese pH Range 5.1-6.2 6.2-6.4 6.6-6.8 2.9-4.7 2.9-3.3 3.4-4.5 4.8-6.0 4.9-5.2 7.3 6.5-6.6 4.9-5.9 pH RANGES FOR FOODS

28. Conditions Affecting Bacterial Growth TIME • Under optimal conditions, some bacteria can double every 20 minutes. • The colder the storage temperature, the longer the potential shelflife. • Potentially hazardous foods should not remain in the danger zone (50-140F) for more than 4 hours during the entire food handling process.

29. Conditions Affecting Bacterial Growth TEMPERATURE *Bacterial proliferation can be controlled by both heat and cold. • Bacteria generally do not grow at freezer temperatures but they can survive. • Use of refrigeration temperatures (30-45F) slows down the rate of bacterial proliferation. The colder the better.

30. Degrees F 250 212 160 148 137 140-50 90 70 60 40 32 28 14 Bacterial Action Resistant spores killed Boiling point of water Resistant Salmonella kill Vegetative cells killed Trichina killed DANGER ZONE Bacteria double-20 min Bacteria double-1 hour Bacteria double-2 hours Bacteria double –6 hours Bacteria double-20 hours Bacteria double –60 hours Lower limit for bacteria BACTERIAL THERMOMETER

31. The Use of Heat • There are two important words to define; *Pasteurization refers to the cooking of food where only a certain number of bacteria are killed. Pasteurization does not render the product sterile. *Sterilization refers to the total destruction of all living organisms and is only found in canned shelf- stable items.

32. The Use of Heat • Clostridium botulinum is a bacteria that can form a spore that is very resistant to heat. It produces a toxin that causes paralysis and is often fatal. It grows well in an anaerobic (no oxygen), warm (60-115F) environment. • Unless a food goes through the canning procedure (cook in a retort or pressure device of 240-250F for several hours) it is assumed to have Clostridium spores present .

33. Photo courtesy of USDA

34. The Use of Heat • Remember that Clostridium grow best at 60-115F so you must cool all foods fast after heating. • Remember to assume that all foods except shelf-stable canned foods and high acid foods contain Clostridium spores and treat them with the proper precautions.

35. Conditions Affecting Bacterial Growth OXYGEN • Some bacteria require oxygen to grow (aerobic). • Some bacteria will not grow in the presence of oxygen (anaerobic). • Most bacteria responsible for food spoilage require oxygen. Most pathogenic bacteria are anaerobic,

36. Conditions Affecting Bacterial Growth MOISTURE • The amount of water available in food for chemical reactions and microbial growth is called water activity (Aw). • Water activity is measured from 0 (totally dry) to 1.0 (pure water). • Most bacteria can only grow in foods that have a water activity higher than 0.90. • The water activity available in foods can be reduced by freezing, dehydration or by adding salt or sugar or other water binders.

37. Aw/ Microorganism 1.0-0.95 Bacteria 0.95-0.91 Bacteria 0.91-0.87 Yeasts 0.87-0.80 Molds 0.30-0.20 No microorganisms proliferate Foods Meat, fish, sausage, milk Moist cheeses, cured meat (ham), fruit juice conc Fermented sausages (salami), dry cheeses, margarine Juice conc, syrups, flour, fruit cakes, honey, jellies, preserves Cookies, crackers, bread crusts WATER ACTIVITY

38. Where do Bacteria come from?

39. Bacterial Origins • We have learned earlier that bacteria can double every so often depending on the environment. • Most food microbiologists would agree that the single most important thing we can do to control bacteria spoilage in the finished product is to keep the bacterial counts as low as possible initially and along the food processing channel. • Where do bacteria enter the food channel? We will now go through the areas of introduction of bacteria into the food channel.

40. #1; Environment from which originally obtained • Were vegetables obtained where manure or compost were used? Were rodents such as mice, raccoons, etc allowed to frequent the field where these were harvested? Were some crops that were infected with disease comingled with uninfected product? • Were animals destined to slaughter covered with manure? • Were eggs and milk harvested from birds and cows in a sanitary manner?

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42. #2; Microbiological quality of raw/unprocessed food • Was the milk on the farm kept cold and obtained from cows in a sanitary manner? • Was the harvesting equipment used and people harvesting the raw products clean and sanitary?

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44. #3; Sanitary conditions of processing • Was the food processing line properly cleaned and sanitized.? • Were the people instructed on sanitary operating procedures ? (e.g. the wearing of hairnets, plastic gloves etc) • Was attention given to proper cooking and cooling requirements?.

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46. #4; Adequacy of packaging, handling and storage • Were refrigerated trucks and warehouses kept cold enough to prevent microbial proliferation?. • Was the product adequately packaged for the shelflife required?. • Was the product distributed, sold and eaten by the ultimate consumer within the allotted shelflife period specified?

47. Photo courtesy of USDA

48. Types of Bacteria on Foods What are the general types of bacteria found on various food products??

49. Red Meat • The muscle of livestock (beef and hogs) is considered fairly sterile while the animal is alive, however within several hours after the animal dies, the immune system ceases to function and bacteria from the gut begin to migrate through the intestinal walls toward the muscle itself. • In addition, after slaughter, the hide is removed causing bacteria from the hide to be released into the air, some of which fall back onto the muscle surface.

50. Red Meat • Bacteria from the intestinal tract include Enterobacter, Micrococcus and Proteus. • Bacteria that are on the surface of carcasses include Pseudomonas, Micrococcus, Corynebacterium, Proteus, Aeromonas, Moraxella, Acinetobacter, Escherichia and Enterobacter. • All of these are ubiquitous inhabitants of the common environment