introduction to food microbiology 1105

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INTRODUCTION TO FOOD MICROBIOLOGY

1105

Steven C SeidemanSteven C Seideman

Extension Food Processing SpecialistExtension Food Processing Specialist

Cooperative Extension ServiceCooperative Extension Service

University of ArkansasUniversity of Arkansas

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Introduction to Food Microbiology

This module covers the fundamental aspects of This module covers the fundamental aspects of bacteria in food starting with the history, what bacteria in food starting with the history, what they are and how they grow, classification systems they are and how they grow, classification systems and types of bacteria found in foods.and types of bacteria found in foods.

It focuses primarily on bacteria responsible for It focuses primarily on bacteria responsible for food spoilage. Pathogens, bacteria that cause food food spoilage. Pathogens, bacteria that cause food poisoning, are discussed more extensively in poisoning, are discussed more extensively in another module (Introduction to Foodborne another module (Introduction to Foodborne Pathogens; 1120).Pathogens; 1120).

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Introduction

Microbiology is the study of living forms so Microbiology is the study of living forms so small that they can only be seen with the aid small that they can only be seen with the aid of a microscope.of a microscope.

They have been referred to as germs, They have been referred to as germs, microbes, bacteria and microorganisms.microbes, bacteria and microorganisms.

4Photo courtesy of USDA

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Photo courtesy of USDA

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History

In the early 1700s Leeuwenhoek, the inventor of In the early 1700s Leeuwenhoek, the inventor of the microscope was first to observe these the microscope was first to observe these microscopic living forms. He referred to them as microscopic living forms. He referred to them as “wee beasties”.“wee beasties”.

In 1810, Nicholas Appert, a French confectioner, In 1810, Nicholas Appert, a French confectioner, place food in glass jars, sealed them and heated place food in glass jars, sealed them and heated them in boiling water. He did not know at the time them in boiling water. He did not know at the time that we was killing spoilage bacteria and invented that we was killing spoilage bacteria and invented what is known today as “canning”.what is known today as “canning”.

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History

In the 1860s, Louis Pasteur showed that certain In the 1860s, Louis Pasteur showed that certain microorganisms were responsible for fermentation microorganisms were responsible for fermentation and decay. He developed the application of heat to and decay. He developed the application of heat to reduce the number of bacteria which now bears his reduce the number of bacteria which now bears his name (e.g. Pasteurization).name (e.g. Pasteurization).

In 1895, the Massachusetts Institute of In 1895, the Massachusetts Institute of Technology determined that mysterious spoilage Technology determined that mysterious spoilage of some canned foods resulted from the failure to of some canned foods resulted from the failure to apply sufficient heat to destroy microorganisms.apply sufficient heat to destroy microorganisms.

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Biodegradable

Food is “biodegradable” meaning it is degraded Food is “biodegradable” meaning it is degraded back into nature often referred to as “spoilage”.back into nature often referred to as “spoilage”.

Microorganisms cause this transition. Microorganisms cause this transition. The environment is filled with microorganisms-The environment is filled with microorganisms-

the air we breathe, the soil, it’s everywhere the air we breathe, the soil, it’s everywhere including in our food. including in our food.

It is our job as food professionals to control these It is our job as food professionals to control these microorganisms before they destroy our food.microorganisms before they destroy our food.

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Microorganisms

There are hundreds of types of There are hundreds of types of microorganisms;microorganisms;

*Some cause food spoilage*Some cause food spoilage

*Some do absolutely nothing*Some do absolutely nothing

*Some are beneficial*Some are beneficial

*Some cause foodborne illness*Some cause foodborne illness

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Beneficial Microorganisms

Used to make fermented foods and Used to make fermented foods and beverages such as beer, wine, sauerkraut, beverages such as beer, wine, sauerkraut, breads, cheeses, pepperoni and other breads, cheeses, pepperoni and other fermented products.fermented products.

Antibiotics-penicillin from moldAntibiotics-penicillin from mold EnzymesEnzymes Fermentation in ruminants.Fermentation in ruminants.

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Pathogens

Pathogens are those bacteria that cause foodborne Pathogens are those bacteria that cause foodborne illness.illness.

Although there are hundreds of species of Although there are hundreds of species of pathogens, the vast majority of foodborne illnesses pathogens, the vast majority of foodborne illnesses are caused by just 4 bacteriaare caused by just 4 bacteria

*Salmonella sp*Salmonella sp *Campylobacter*Campylobacter *Staphylococcus aureus*Staphylococcus aureus *Clostridium perfringens*Clostridium perfringens

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Bacteria

Although yeasts, molds and bacteria make Although yeasts, molds and bacteria make up the category of microorganisms, we will up the category of microorganisms, we will not be discussing yeasts and mold to any not be discussing yeasts and mold to any great extent in this module.great extent in this module.

We will focus primarily on bacteria since We will focus primarily on bacteria since they are the main cause of food spoilage.they are the main cause of food spoilage.

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Bacteria

Bacteria are most important and troublesome for Bacteria are most important and troublesome for the food processor.the food processor.

Most bacteria are harmless in themselves but Most bacteria are harmless in themselves but produce excretions and enzymes that result in food produce excretions and enzymes that result in food spoilage. spoilage.

They are single-celled living bodies that are They are single-celled living bodies that are 1/1,000 to 1/25,000 of an inch in length.1/1,000 to 1/25,000 of an inch in length.

The number of these tiny organisms that could be The number of these tiny organisms that could be placed on the head of a pin would equal the placed on the head of a pin would equal the population of New York City.population of New York City.

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Bacterial Growth

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

Under optimum conditions, bacteria can double Under optimum conditions, bacteria can double every 20-30 minutes. every 20-30 minutes.

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BACTERIAL GROWTH

Food is generally considered spoiled when the Food is generally considered spoiled when the bacterial counts exceed 10bacterial counts exceed 10 6 6 or 10or 1077. This is . This is 1,000,000 to 10,000,000 bacteria per gram.1,000,000 to 10,000,000 bacteria per gram.

Most spoilage is a surface phenomenon occurring Most spoilage is a surface phenomenon occurring only on the surface of food unless the food is only on the surface of food unless the food is ground or mixed such as sausage where spoilage ground or mixed such as sausage where spoilage occurs on the inside.occurs on the inside.

Bacterial slime is generally on the order of 10Bacterial slime is generally on the order of 1088..

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Bacterial Classifications Bacteria can be classified in a number of ways.Bacteria can be classified in a number of ways. **Their shapeTheir shape-Round=cocci-Round=cocci Elongated=rodsElongated=rods **SporeformingSporeforming; Some rod shaped bacteria are ; Some rod shaped bacteria are

sporeformers. This is a dormant stage in their life sporeformers. This is a dormant stage in their life cycle. These spores have the ability to survive a cycle. These spores have the ability to survive a wide range of environmental extremes. They can wide range of environmental extremes. They can survive heating up to 212F and are resistant to survive heating up to 212F and are resistant to most chemicals including sanitizing solutions. The most chemicals including sanitizing solutions. The most noteworthy sporeformer is Clostridium most noteworthy sporeformer is Clostridium Botulinum.Botulinum.

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Bacterial Classifications

*Based on oxygen requirements;*Based on oxygen requirements;

AerobicAerobic-Need oxygen to grow-Need oxygen to grow

AnaerobicAnaerobic-Can grow only if oxygen is -Can grow only if oxygen is absentabsent

FacultativeFacultative-Can grow with or without -Can grow with or without oxygen.oxygen.

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Based on optimum temperature for growth;Based on optimum temperature for growth;

*Psychro=cold*Psychro=cold

*Meso = middle*Meso = middle

*Thermo= warm*Thermo= warm

*Trophic =growing*Trophic =growing

*Duric=withstand*Duric=withstand

*Phil or philic-prefers*Phil or philic-prefers

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PsychrotropicPsychrotropic-grow best at 58-68F but can -grow best at 58-68F but can grow slowly at refrigeration temperatures grow slowly at refrigeration temperatures (32-50F).(32-50F).

MesophilicMesophilic-Grows best at 86-98F . Most -Grows best at 86-98F . Most food spoilage bacteria grow very well at food spoilage bacteria grow very well at these temperatures.these temperatures.

ThermophilicThermophilic-Grow best at 100-150F. Most -Grow best at 100-150F. Most sporeformers fit in this group.sporeformers fit in this group.

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CONDITIONS AFFECTING BACTERIAL GROWTH

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CONDITIONS AFFECTING BACTERIAL GROWTH

There are 6 conditions affecting bacterial growth There are 6 conditions affecting bacterial growth and can be remembered by the anagram and can be remembered by the anagram

FAT TOM.FAT TOM. FoodFood

AcidityAcidity TimeTime

TemperatureTemperature OxygenOxygen MoistureMoisture

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Conditions Affecting Bacterial Growth

FOODFOOD Bacteria need food to reproduce.Bacteria need food to reproduce. High protein foods and moist starchy foods High protein foods and moist starchy foods

promote bacterial growth but any food can promote bacterial growth but any food can be potentially risky is not handled properly.be potentially risky is not handled properly.

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ACIDITY ACIDITY pH-measure of acidity or alkalinity. (pH =7 is pH-measure of acidity or alkalinity. (pH =7 is

neutral; 1=acid; 14=basic).neutral; 1=acid; 14=basic). Most bacteria prefer a pH of 5.5-7.5.Most bacteria prefer a pH of 5.5-7.5. Most bacteria, especially pathogens, will not grow Most bacteria, especially pathogens, will not grow

at a pH of 4.6 or less (acid). This is why at a pH of 4.6 or less (acid). This is why fermented foods such as sauerkraut (fermented fermented foods such as sauerkraut (fermented cabbage) and fermented sausages were historically cabbage) and fermented sausages were historically used in Europe.used in Europe.

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pH RANGES OF BACTERIA

BacteriaBacteria

MoldsMolds

YeastsYeasts

SalmonellaSalmonella

Clostridium BotuliumClostridium Botulium

Clostridium perfringensClostridium perfringens

Listeria monocytogenesListeria monocytogenes

CampylobacterCampylobacter

pH RangepH Range

0.5-110.5-11

1.5-8.51.5-8.5

4.5-9.54.5-9.5

4.8-8.34.8-8.3

5.0-8.55.0-8.5

4.6-9.64.6-9.6

5.0-9.05.0-9.0

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pH RANGES FOR FOODS FoodFood MeatMeat ChickenChicken FishFish FruitFruit ApplesApples GrapesGrapes VegetablesVegetables CarrotCarrot CornCorn DairyDairy MilkMilk CheeseCheese

pH RangepH Range5.1-6.25.1-6.26.2-6.46.2-6.46.6-6.86.6-6.82.9-4.72.9-4.7 2.9-3.32.9-3.3 3.4-4.53.4-4.54.8-6.04.8-6.0 4.9-5.24.9-5.2 7.37.3

6.5-6.66.5-6.6 4.9-5.94.9-5.9

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Conditions Affecting Bacterial Growth TIMETIME Under optimal conditions, some bacteria can Under optimal conditions, some bacteria can

double every 20 minutes.double every 20 minutes. The colder the storage temperature, the longer the The colder the storage temperature, the longer the

potential shelflife.potential shelflife. Potentially hazardous foods should not remain in Potentially hazardous foods should not remain in

the danger zone (50-140F) for more than 4 hours the danger zone (50-140F) for more than 4 hours during the entire food handling process.during the entire food handling process.

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Conditions Affecting Bacterial Growth TEMPERATURETEMPERATURE*Bacterial proliferation can be controlled by *Bacterial proliferation can be controlled by

both heat and cold.both heat and cold. Bacteria generally do not grow at freezer Bacteria generally do not grow at freezer

temperatures but they can survive.temperatures but they can survive. Use of refrigeration temperatures (30-45F) Use of refrigeration temperatures (30-45F)

slows down the rate of bacterial slows down the rate of bacterial proliferation. The colder the better.proliferation. The colder the better.

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Degrees FDegrees F 250250 212212 160160 148148 137137 140-50140-50 9090 7070 6060 4040 3232 2828 14 14

Bacterial ActionBacterial ActionResistant spores killedResistant spores killedBoiling point of waterBoiling point of waterResistant Salmonella killResistant Salmonella killVegetative cells killedVegetative cells killedTrichina killedTrichina killedDANGER ZONEDANGER ZONEBacteria double-20 minBacteria double-20 minBacteria double-1 hourBacteria double-1 hourBacteria double-2 hoursBacteria double-2 hoursBacteria double –6 hoursBacteria double –6 hoursBacteria double-20 hoursBacteria double-20 hoursBacteria double –60 hoursBacteria double –60 hoursLower limit for bacteriaLower limit for bacteria

BACTERIAL THERMOMETER

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The Use of Heat

There are two important words to define;There are two important words to define; **PasteurizationPasteurization refers to the cooking of food refers to the cooking of food

where only a certain number of bacteria are where only a certain number of bacteria are killed. Pasteurization does not render the killed. Pasteurization does not render the product sterile.product sterile.

**SterilizationSterilization refers to the total destruction refers to the total destruction of all living organisms and is only found in of all living organisms and is only found in canned shelf- stable items.canned shelf- stable items.

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The Use of Heat

Clostridium botulinum is a bacteria that can form Clostridium botulinum is a bacteria that can form a spore that is very resistant to heat. It produces a a spore that is very resistant to heat. It produces a toxin that causes paralysis and is often fatal. It toxin that causes paralysis and is often fatal. It grows well in an anaerobic (no oxygen), warm grows well in an anaerobic (no oxygen), warm (60-115F) environment.(60-115F) environment.

Unless a food goes through the canning procedure Unless a food goes through the canning procedure (cook in a retort or pressure device of 240-250F (cook in a retort or pressure device of 240-250F for several hours) it is assumed to have for several hours) it is assumed to have Clostridium spores present . Clostridium spores present .

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The Use of Heat

Remember that Clostridium grow best at Remember that Clostridium grow best at 60-115F so you must cool all foods fast 60-115F so you must cool all foods fast after heating.after heating.

Remember to assume that all foods except Remember to assume that all foods except shelf-stable canned foods and high acid shelf-stable canned foods and high acid foods contain Clostridium spores and treat foods contain Clostridium spores and treat them with the proper precautions.them with the proper precautions.

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OXYGENOXYGEN Some bacteria require oxygen to grow (aerobic).Some bacteria require oxygen to grow (aerobic). Some bacteria will not grow in the presence of Some bacteria will not grow in the presence of

oxygen (anaerobic).oxygen (anaerobic). Most bacteria responsible for food spoilage Most bacteria responsible for food spoilage

require oxygen. Most pathogenic bacteria are require oxygen. Most pathogenic bacteria are anaerobic,anaerobic,

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MOISTUREMOISTURE The amount of water available in food for chemical The amount of water available in food for chemical

reactions and microbial growth is called water activity reactions and microbial growth is called water activity (Aw).(Aw).

Water activity is measured from 0 (totally dry) to 1.0 Water activity is measured from 0 (totally dry) to 1.0 (pure water).(pure water).

Most bacteria can only grow in foods that have a water Most bacteria can only grow in foods that have a water activity higher than 0.90.activity higher than 0.90.

The water activity available in foods can be reduced by The water activity available in foods can be reduced by freezing, dehydration or by adding salt or sugar or other freezing, dehydration or by adding salt or sugar or other water binders.water binders.

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WATER ACTIVITY Aw/ MicroorganismAw/ Microorganism1.0-0.95 Bacteria1.0-0.95 Bacteria

0.95-0.91 Bacteria0.95-0.91 Bacteria

0.91-0.87 Yeasts0.91-0.87 Yeasts

0.87-0.80 Molds0.87-0.80 Molds

0.30-0.20 No microorganisms 0.30-0.20 No microorganisms proliferateproliferate

FoodsFoodsMeat, fish, sausage, milkMeat, fish, sausage, milk

Moist cheeses, cured meat (ham), Moist cheeses, cured meat (ham), fruit juice concfruit juice conc

Fermented sausages (salami), dry Fermented sausages (salami), dry cheeses, margarinecheeses, margarine

Juice conc, syrups, flour, fruit Juice conc, syrups, flour, fruit cakes, honey, jellies, preservescakes, honey, jellies, preserves

Cookies, crackers, bread crustsCookies, crackers, bread crusts

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Where do Bacteria come from?

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Bacterial Origins We have learned earlier that bacteria can double We have learned earlier that bacteria can double

every so often depending on the environment.every so often depending on the environment. Most food microbiologists would agree that the Most food microbiologists would agree that the

single most important thing we can do to control single most important thing we can do to control bacteria spoilage in the finished product is to keep bacteria spoilage in the finished product is to keep the bacterial counts as low as possible initially and the bacterial counts as low as possible initially and along the food processing channel.along the food processing channel.

Where do bacteria enter the food channel?Where do bacteria enter the food channel? We will now go through the areas of introduction We will now go through the areas of introduction

of bacteria into the food channel.of bacteria into the food channel.

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#1; Environment from which originally obtained

Were vegetables obtained where manure or Were vegetables obtained where manure or compost were used? Were rodents such as mice, compost were used? Were rodents such as mice, raccoons, etc allowed to frequent the field where raccoons, etc allowed to frequent the field where these were harvested? Were some crops that were these were harvested? Were some crops that were infected with disease comingled with uninfected infected with disease comingled with uninfected product?product?

Were animals destined to slaughter covered with Were animals destined to slaughter covered with manure?manure?

Were eggs and milk harvested from birds and Were eggs and milk harvested from birds and cows in a sanitary manner?cows in a sanitary manner?

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#2; Microbiological quality of raw/unprocessed food

Was the milk on the farm kept cold and Was the milk on the farm kept cold and obtained from cows in a sanitary manner?obtained from cows in a sanitary manner?

Was the harvesting equipment used and Was the harvesting equipment used and people harvesting the raw products clean people harvesting the raw products clean and sanitary?and sanitary?

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#3; Sanitary conditions of processing

Was the food processing line properly cleaned and Was the food processing line properly cleaned and sanitized.?sanitized.?

Were the people instructed on sanitary operating Were the people instructed on sanitary operating procedures ? (e.g. the wearing of hairnets, plastic procedures ? (e.g. the wearing of hairnets, plastic gloves etc)gloves etc)

Was attention given to proper cooking and cooling Was attention given to proper cooking and cooling requirements?.requirements?.

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#4; Adequacy of packaging, handling and storage

Were refrigerated trucks and warehouses Were refrigerated trucks and warehouses kept cold enough to prevent microbial kept cold enough to prevent microbial proliferation?.proliferation?.

Was the product adequately packaged for Was the product adequately packaged for the shelflife required?.the shelflife required?.

Was the product distributed, sold and eaten Was the product distributed, sold and eaten by the ultimate consumer within the allotted by the ultimate consumer within the allotted shelflife period specified?shelflife period specified?

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Types of Bacteria on Foods

What are the general types of bacteria What are the general types of bacteria found on various food products??found on various food products??

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Red Meat

The muscle of livestock (beef and hogs) is The muscle of livestock (beef and hogs) is considered fairly sterile while the animal is alive, considered fairly sterile while the animal is alive, however within several hours after the animal however within several hours after the animal dies, the immune system ceases to function and dies, the immune system ceases to function and bacteria from the gut begin to migrate through the bacteria from the gut begin to migrate through the intestinal walls toward the muscle itself. intestinal walls toward the muscle itself.

In addition, after slaughter, the hide is removed In addition, after slaughter, the hide is removed causing bacteria from the hide to be released into causing bacteria from the hide to be released into the air, some of which fall back onto the muscle the air, some of which fall back onto the muscle surface.surface.

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Red Meat

Bacteria from the intestinal tract include Bacteria from the intestinal tract include Enterobacter, Micrococcus and Proteus.Enterobacter, Micrococcus and Proteus.

Bacteria that are on the surface of carcasses Bacteria that are on the surface of carcasses include Pseudomonas, Micrococcus, include Pseudomonas, Micrococcus, Corynebacterium, Proteus, Aeromonas, Corynebacterium, Proteus, Aeromonas, Moraxella, Acinetobacter, Escherichia and Moraxella, Acinetobacter, Escherichia and Enterobacter.Enterobacter.

All of these are ubiquitous inhabitants of the All of these are ubiquitous inhabitants of the common environmentcommon environment

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Common Types of Spoilage of Fresh Meats

Souring Souring (aerobic)-Chromobacterium, (aerobic)-Chromobacterium, Pseudomonas, Lactobacillus.Pseudomonas, Lactobacillus.

PutrefactionPutrefaction-Clostridium, Pseudomonas, -Clostridium, Pseudomonas, Chromobacterium, Proteus.Chromobacterium, Proteus.

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Ground Meat & Sausages By the act of grinding meat, any surface bacteria By the act of grinding meat, any surface bacteria

are further distributed into the interior of the meat.are further distributed into the interior of the meat. In addition, the grinding of the meat releases more In addition, the grinding of the meat releases more

juices improving the environmental conditions juices improving the environmental conditions (increased Aw) that promote bacterial (increased Aw) that promote bacterial proliferation.proliferation.

Retail packages of sausages such as weiners and Retail packages of sausages such as weiners and bologna often have a milky-looking juice inside. bologna often have a milky-looking juice inside. These are usually lactic-acid bacteria that ferment These are usually lactic-acid bacteria that ferment the sugar in the sausage to lactic acid.the sugar in the sausage to lactic acid.

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Common Types of Spoilage of Cured Meats SouringSouring-Chromobacterium, Bacillus, -Chromobacterium, Bacillus,

Pseudomonas, Pseudomonas, GreeningGreening-Lactobacillus-Lactobacillus SlimySlimy-Leuconostoc-Leuconostoc

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Poultry

Poultry are very similar to red meat in Poultry are very similar to red meat in intestinal bacteria and surface bacteria to intestinal bacteria and surface bacteria to include Enterobacteriaceae, Pseudomonas, include Enterobacteriaceae, Pseudomonas, Bacillus, Micrococcus, Corynebacterium, Bacillus, Micrococcus, Corynebacterium, Proteus, Chromobacterium, Escherichia and Proteus, Chromobacterium, Escherichia and Enterobacter.Enterobacter.

Salmonella is quite common in poultrySalmonella is quite common in poultry

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Common Types of Spoilage of Poultry

Odor & SlimeOdor & Slime-Chromobacterium, -Chromobacterium, Pseudomonas, AlcaligenesPseudomonas, Alcaligenes

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Fish & Shellfish

Bacteria from the genera Pseudomonas, Bacteria from the genera Pseudomonas, Chromobacterium, Micrococcus, Chromobacterium, Micrococcus, Flavobacterium, Corynebacterium, Sarcina Flavobacterium, Corynebacterium, Sarcina and Serratia have been associated with and Serratia have been associated with slimy coats on fish.slimy coats on fish.

Intestinal flora may include species of the Intestinal flora may include species of the genera Bacillus, Escherichia and genera Bacillus, Escherichia and Clostridium.Clostridium.

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Common Types of Spoilage of Fish

DiscolorationDiscoloration-Pseudomonas-Pseudomonas PutrefactionPutrefaction-Chromobacterium, -Chromobacterium,

FlavobacteriumFlavobacterium

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Fruits & Vegetables

The tissues of the internal parts of fruits and The tissues of the internal parts of fruits and vegetables are like meat-considered sterile.vegetables are like meat-considered sterile.

It is the exterior surface that harbors the bacteria. It is the exterior surface that harbors the bacteria. Manure used as fertilizer represents a potential Manure used as fertilizer represents a potential

problem.problem. Vegetables growing in the soil such as root crops Vegetables growing in the soil such as root crops

contain species of Bacillus, Pseudomonas and contain species of Bacillus, Pseudomonas and many others.many others.

Soils and plants harbor Lactobacillus, Soils and plants harbor Lactobacillus, Leuconostoc and Pediococcus.Leuconostoc and Pediococcus.

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Common Types of Spoilage of Fruits and Vegetables

Bacterial soft rotBacterial soft rot-Erwinia carotovora-Erwinia carotovora Sliminess or souringSliminess or souring-Saprophytic bacteria-Saprophytic bacteria

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Common Types of Spoilage of Fruit and Vegetable Juice

Off-flavorOff-flavor-Lactobacillus-Lactobacillus SouringSouring-Lactobacillus, Acinetobacter-Lactobacillus, Acinetobacter

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Common Spoilage of Sugar Products (Honey, Syrups)

Ropy or stringy syrupRopy or stringy syrup-Enterobacter -Enterobacter aerogenesaerogenes

Green syrupGreen syrup-Pseudomonas fluorescens-Pseudomonas fluorescens Gassy or frothy molassesGassy or frothy molasses-Clostridium-Clostridium

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Fermented Foods

Soil and plants harbor large numbers of Soil and plants harbor large numbers of Lactobacillus, Leuconostoc and Pediococcus.Lactobacillus, Leuconostoc and Pediococcus.

In fermented products such as pickles, sauerkraut In fermented products such as pickles, sauerkraut and olives, we allow these natural occurring and olives, we allow these natural occurring bacteria to convert carbohydrates to lactic acid bacteria to convert carbohydrates to lactic acid thereby lowering the pH.thereby lowering the pH.

The bacterial selection is conducted by using high The bacterial selection is conducted by using high salt solutions (called brines) that allow only salt solutions (called brines) that allow only certain types of bacteria to live. certain types of bacteria to live.

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Common Types of Spoilage of Fermented Vegetables

Slimy krautSlimy kraut-Lactobacillus plantarum-Lactobacillus plantarum Soft picklesSoft pickles-Bacillus-Bacillus Black picklesBlack pickles-Bacillus nigrificans-Bacillus nigrificans

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Egg & Egg Products

Eggs like meat are considered virtually sterile on Eggs like meat are considered virtually sterile on the inside but the outside surface of the shell will the inside but the outside surface of the shell will have bacteria. Over time, these bacteria will have bacteria. Over time, these bacteria will invade the inside of the egg. invade the inside of the egg.

Salmonella is a big concern with eggs and egg Salmonella is a big concern with eggs and egg products. products.

Egg products such as liquid eggs may contain the Egg products such as liquid eggs may contain the bacteria that were on the surface of the egg.bacteria that were on the surface of the egg.

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Common Types of Spoilage of Eggs

Green rotGreen rot-Pseudomonas fluorescens-Pseudomonas fluorescens Colorless rotColorless rot-Pseudomonas, -Pseudomonas,

ChrombacteriumChrombacterium Black rotBlack rot-Proteus-Proteus

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A Word about Pathogens

Pathogens are bacteria that cause food poisoning.Pathogens are bacteria that cause food poisoning. More detail on pathogens can be found elsewhere More detail on pathogens can be found elsewhere

in this educational series.in this educational series. Foodborne illness is far more common than most Foodborne illness is far more common than most

people realize. Often confused with the flu.people realize. Often confused with the flu. Some cause only flu-like symptoms for a few days Some cause only flu-like symptoms for a few days

while some are fatal such as botulism. while some are fatal such as botulism.

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Some Pathogens

Common PathogensCommon Pathogens

* Campylobacter jejuni* Campylobacter jejuni

*Salmonella*Salmonella

*Staphylococcus *Staphylococcus

aureusaureus

*Clostridium *Clostridium

perfringensperfringens

Deadly/RareDeadly/Rare

*Clostridium *Clostridium

botulinumbotulinum

*Listeria *Listeria

monocytogenesmonocytogenes

*E. coli 0157;H7*E. coli 0157;H7

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Listeria Monocytogenes; Photo courtesy of USDA

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Salmonella Enteritis; Photo courtesy of USDA

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Campylobacter Fetus; Photo courtesy of USDA

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FOOD PRESERVATION

How we can keep food fresh and How we can keep food fresh and safe????safe????

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Food Preservation

Food is designed by Mother Nature to spoil. This Food is designed by Mother Nature to spoil. This now has a term-”Biodegradable”.now has a term-”Biodegradable”.

Eggs, milk and meat are perfect bacterial growth Eggs, milk and meat are perfect bacterial growth mediums.mediums.

Food is extremely “biodegradable” and as food Food is extremely “biodegradable” and as food professionals, our job evolves around finding and professionals, our job evolves around finding and implementing steps that keep food from spoiling implementing steps that keep food from spoiling and reduce or eliminate the pathogens that might and reduce or eliminate the pathogens that might be present.be present.

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Controlling Bacteria

Controlling bacteria in foods has been going on Controlling bacteria in foods has been going on for centuries starting with the caveman for centuries starting with the caveman discovering fire to cook meat, the use of saltpeter discovering fire to cook meat, the use of saltpeter by Egyptians to cure meat through Europeans by Egyptians to cure meat through Europeans making fermented, dried sausages. making fermented, dried sausages.

Leviticus and Deuteronomy chapters of the Old Leviticus and Deuteronomy chapters of the Old Testament in the Bible have numerous references Testament in the Bible have numerous references on what to eat and how food should be prepared.on what to eat and how food should be prepared.

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Most of the old methods of food preservation were Most of the old methods of food preservation were most probably discovered by accident with the most probably discovered by accident with the theory of “let’s see if this works” or by long term theory of “let’s see if this works” or by long term observation.observation.

Over the last 100 years, mainly since the Over the last 100 years, mainly since the discovery of bacteria, great strides have been discovery of bacteria, great strides have been made at discovering how to preserve food mainly made at discovering how to preserve food mainly through the study of microbiology.through the study of microbiology.

Food preservation has gone from an art to a Food preservation has gone from an art to a sciencescience

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There are basically 5 categories of things There are basically 5 categories of things we know we can do to control bacteria.we know we can do to control bacteria.

*Control initial bacteria counts*Control initial bacteria counts

*Control and use of temperature*Control and use of temperature

*Control oxygen*Control oxygen

*Control moisture*Control moisture

*Control acidity*Control acidity

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Control Initial Bacteria Counts

The single most important control factor is The single most important control factor is that of keeping the initial bacteria counts on that of keeping the initial bacteria counts on raw food as low as possible. raw food as low as possible.

Most other control methods only reduce Most other control methods only reduce bacterial counts by a percentage. Example; bacterial counts by a percentage. Example; Cooking may reduce bacteria by 90%; What Cooking may reduce bacteria by 90%; What would you prefer? Having 10% of 100=10 would you prefer? Having 10% of 100=10 bacteria or 10% of 1,000=100 bacteria???. bacteria or 10% of 1,000=100 bacteria???.

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Control Initial Bacteria Counts.

We can do this by working to keep raw We can do this by working to keep raw material as clean as possible during harvest, material as clean as possible during harvest, proper cleaning of food processing proper cleaning of food processing facilities, use of sanitizing solutions such as facilities, use of sanitizing solutions such as chlorine in processing plants, the use of chlorine in processing plants, the use of chlorinated water during processing and chlorinated water during processing and instruction of people in food processing of instruction of people in food processing of important hygiene issues.important hygiene issues.

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Temperature

Bacterial proliferation can be controlled by Bacterial proliferation can be controlled by both heat and cold.both heat and cold.

Bacteria generally do not grow at freezer Bacteria generally do not grow at freezer temperatures but they can survive.temperatures but they can survive.

Use of refrigeration temperatures (30-45F) Use of refrigeration temperatures (30-45F) slows down the rate of bacterial slows down the rate of bacterial proliferation. The colder the better.proliferation. The colder the better.

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Pasteurization

Most food is only pasteurized meaning that the bacterial Most food is only pasteurized meaning that the bacterial population has been drastically reduced on the order of 90-95%.population has been drastically reduced on the order of 90-95%.

Most bacteria are very sensitive to heat and are easily killed.Most bacteria are very sensitive to heat and are easily killed. Milk is a good example. Milk is heated to a high temperature Milk is a good example. Milk is heated to a high temperature

(161F) for a very short period of time (15 seconds) reducing the (161F) for a very short period of time (15 seconds) reducing the bacteria population but it will still spoil due to unkilled bacteria bacteria population but it will still spoil due to unkilled bacteria after extended refrigerated storage.after extended refrigerated storage.

Milk pasteurized started in the early 1950s mainly to reduce the Milk pasteurized started in the early 1950s mainly to reduce the incidence of tuberculosis caused by Mycobacterium incidence of tuberculosis caused by Mycobacterium tuberculosis.tuberculosis.

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Control Oxygen

There are a number of spoilage bacteria that There are a number of spoilage bacteria that require oxygen to grow (aerobics).require oxygen to grow (aerobics).

By eliminating oxygen from the food, we By eliminating oxygen from the food, we can drastically slow down decomposition. can drastically slow down decomposition. Note the number of meat products sold in Note the number of meat products sold in vacuum packages. Some foods can also be vacuum packages. Some foods can also be distributed in nitrogen atmospheres which is distributed in nitrogen atmospheres which is a method of displacing oxygen.a method of displacing oxygen.

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Control Moisture

Drying of food products is certainly not new. Drying of food products is certainly not new. The control of the water activity (Aw) is the key. The control of the water activity (Aw) is the key.

In high sugar items like honey, jellies and In high sugar items like honey, jellies and molasses do not generally spoil from bacteria molasses do not generally spoil from bacteria because the sugar ties up the available moisture.because the sugar ties up the available moisture.

Cereals and bakery items such as breads do not Cereals and bakery items such as breads do not typically spoil from bacteria because their typically spoil from bacteria because their moisture content is so low.moisture content is so low.

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Control Acidity

By keeping food products in an acidified condition, By keeping food products in an acidified condition, we can control bacteria.we can control bacteria.

Clostridium botulinum will not grow below pH=4.6.Clostridium botulinum will not grow below pH=4.6. Many soft drinks have low pHs to keep them from Many soft drinks have low pHs to keep them from

spoiling by bacteria. spoiling by bacteria. Pickles, olives, sauerkraut are preserved by their low Pickles, olives, sauerkraut are preserved by their low

pH.pH. The old rule was that if you eat acid foods, you will The old rule was that if you eat acid foods, you will

never get food poisoning. Some new exceptions.never get food poisoning. Some new exceptions.

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CONCLUSIONS

Remember that this is only an introductory Remember that this is only an introductory module. The area of food microbiology is very module. The area of food microbiology is very deep and challenging.deep and challenging.

The control of food spoilage goes back in time a The control of food spoilage goes back in time a long way.long way.

Think of the control factors when processing food-Think of the control factors when processing food-FAT TOM.FAT TOM.

Continually strive to reduce and/or eliminate Continually strive to reduce and/or eliminate bacteria in food processing.bacteria in food processing.