1. FOOD PRESERVATION 1121 Steven C Seideman
Extension Food Processing Specialist
Cooperative Extension Service
University of Arkansas
This course is entitled “Food Preservation”

2. INTRODUCTION
Americans tend to take our food supply for granted. Compared to most of the world, we have excellent soil and natural resources that are second to none. Our growth and harvesting of livestock and crops is cutting edge and our food processing technology is state-of-the-art. In addition, our distribution and sales market are tops.
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3. INTRODUCTION
Our food would not be readily available to consumers if foods were not processed in such a manner that they prevent or delay the natural process of decay.
The science behind food preservation can be seen everyday in a supermarket although the preservation method may not be readily known.
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4. Our food stores have numerous food products that are safe, high quality, nutritious and economical

5. If it were not for the knowledge of food science, most of these food products would not be readily available.

6. HISTORY OF FOOD PRESERVATION
The caveman’s discovery of fire was probably the start of food preservation. By cooking meat on a fire,the meat became pasteurized and the shelf-life (time the food product is considered edible) was increased by several days. Then came the advent of drying meat which increased the shelf-life even longer.
Europeans later discovered that cheese and sausages could be preserved by the use of low pH, low moisture content and high salt content.
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7. HISTORY OF FOOD PRESERVATION
Nicholas Appert under Napoleon invented the art of canning. He didn’t know how it worked but he found that food placed in cans or glass jars and heated would keep for a much longer period of time.
During the Revolutionary War, patriots often received barrels of salt pork from Uncle Sam’s Provision Co, hence the expression “Uncle Sam” referring to the U.S. Federal government was derived.
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8. HISTORY OF FOOD PRESERVATION
Starting in the early 1900s, the science of microorganisms along with the science of food gathered momentum and lead to such inventions as refrigeration, freezing, use of chemicals in foods such as sodium lactate and parabens, freeze drying and packaging.
Along with the above came improvements in cooking procedures, blast freezing and other technological advances to existing methods.
Now we are on the doorsteps of food irradiation, radio frequency cooking and other technologies.
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9. Food Preservation
This module is about methods used to preserve food and how they work.
Other educational courses in this series also cover some of the same material but from the standpoint of bacterial spoilage or pathogens.
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10. The Fundamental Concepts of Food Preservation
Basically, all food preservation methods do one or more of the following to prevent the natural biodegradation of food.
*Prevent the proliferation of spoilage bacteria.
*Prevent the proliferation of pathogenic bacteria.
*Prevent the rancidity of fat
*Prevent to work of endogenous autolytic enzymes.
*Prevent the reintroduction of dirt, dust etc after processing (e.g. packaging).
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11. Preventing Proliferation of Spoilage and Pathogenic Bacteria
Bacteria reduce the edibility of food and is, by far, the leading source of degradation of foods.
Whether the bacteria be of the spoilage or pathogenic types, they are bacteria and can be controlled by controlling the following 6 conditions in food.
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12. 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
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13. 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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14. 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
Most pathogenic bacteria 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.
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15. pH VALUES OF BACTERIA Bacteria Molds Yeasts Salmonella
Clostridium Botulium
Clostridium perfringens
Listeria monocytogenes
Campylobacter
pH Range
0.5-11
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16. pH VALUES FOR FOODS Food Meat Chicken Fish Fruit Apples Grapes
Vegetables
Carrot
Corn
Dairy
Milk
Cheese
pH Range
7.3
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17. Conditions Affecting Bacterial Growth
TIME
Under optimal conditions, some bacteria can double every 20 minutes and increase logarithmically.
The colder the storage temperature, the longer the potential shelflife.
Potentially hazardous foods should not remain in the danger zone (40-140F) for more than 4 hours during the entire food handling process.
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18. 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 (30-50F) slows down the rate of bacterial proliferation. The colder the better.
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19. BACTERIAL THERMOMETER
Degrees F
250
212
160
148
137
140-40 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
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20. 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.
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21. The Use of Heat
Clostridium botulinum is a bacteria that can form spores that are 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 212F for several hours) it is assumed to have Clostridium spores present.
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22. Most cooking of foods is a form of pasteurization that dramatically reduces the number of bacteria.
Photo courtesy of USDA

23. The Use of Heat
Remember that Clostridium grow best at F 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.
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24. Conditions Affecting Bacterial Growth
OXYGEN
Some bacteria require oxygen to grow (aerobic).
Some bacteria will only grow if no oxygen is present (anaerobic).
Some bacteria can go with or without oxygen ( facultative).
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25. Conditions Effecting 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 spoilage and pathogenic bacteria can only grow in foods that have a water activity higher than
The water activity available in foods can be reduced by freezing, dehydration or adding salt or sugar.(e.g. honey does not foster bacterial growth).
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26. WATER ACTIVITY Aw/ Microorganism Foods 1.0-0.95 Bacteria
Yeasts
Molds
No microorganism
proliferation
Foods
Meat, fish, sausage, milk
Cheese, 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
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27. Preventing the Rancidity of Fat
Fats tend to go rancid over time.
Almost all foods have some level of fat.
Oxidative rancidity is the term used to explain the generation of a free radical and results in a rapid progression of fat rancidity.
The next slide will show some things that promote rancidity (pro-oxidants) and some things that retard its development (antioxidants).
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28. Affectors of Fat Rancidity
Pro-oxidants
*Salt
*Time
*Heat
*Oxygen
*Irradiation
Antioxidants
*Vitamin C and E
*Sodium nitrite (cured
meats)
*Erythorbate/
Ascorbate
*Smoke components
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29. Fat Rancidity The eating of rancid fat has been shown to cause cancer.
In the same light, diets rich in antioxidants have been shown to prevent cancer.
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30. Prevent the Work of Endogenous, Autolytic Enzymes
Most raw food materials have endogenous, autolytic enzymes that decompose foods.
The best example is that of vegetables that require a heat treatment called “blanching” that denatures the enzymes. If they are not blanched, these vegetables would turn mushy.
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31. Prevent the Reintroduction of Dirt, Dust etc
After food in treated or processed, it needs to be kept clean. This area is known as “packaging”.
Packaging can range from a simply plastic film ( dust cover) all the way to flexible, oxygen impermeable films and even cans and glass/ plastic jars.
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32. Methods of Food Preservation
We have just discussed the fundamental causes of food spoilage.
We can now discuss the basic methods used to control food spoilage.
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33. Methods of Food Preservation
1)Control of temperature
Use of heat
Use of refrigeration/ Freezing
2)Use of Food Ingredients
3)Control of Water Activity
4)Control of pH
5)Packaging
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34. Control of Temperature
USE OF HEAT
The use of heat can range from a mild cook in the kitchen for pasteurization to total sterilization
Pasteurization refers to the application of heat to get a significant reduction in bacteria.
Sterilization refers to the application of a lot of heat and time to render the a food product totally bacteria-free.
Pasteurization is mainly important in the reduction of pathogenic bacteria in milk-legally required.
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35. Control of Temperature
Heating of food also denatures endogenous enzymes (blanching of vegetables).
The science of canning is aimed at the total destruction of all bacteria. The hardest bacteria to kill is the spore-former, Clostridium botulinum which can be lethal.
Cooking can be done in a variety of methods from dry heat methods to deep-fat frying.
All methods are aimed at the destruction, to some degree of bacteria and inactivation of enzymes..
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36. BACTERIAL THERMOMETER
Degrees F
250
212
160
148
137
140-40 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
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37. Heat is the most common form of food preservation because it pasteurizes the product and makes it in an edible form.
Photo courtesy of USDA

38. Control of Temperature
THE USE OF
REFRIGERATION/FREEZING.
Refrigeration (at or above 32F) slows down bacteria proliferation and enzymatic activity.
Freezing (below 32F) dramatically slows down fat rancidity and enzymatic activity but they still happen.Less than 1 year frozen shelf-life.
Freezing does not kill bacteria to any great extent. They just become dormant.
Fast freezing results in smaller ice crystals being formed that do not damage the food structure upon thawing.
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39. SHELFLIFE OF SELECTED FOODS
Chicken (fresh)
Chicken (fried)
Beef
Pork
Bacon/Sausage
Fish
Peaches
Peas/Beans
Raspberries/ Strawberries
Months at –10F 15 1 8 5 2 3
1.5
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40. Use of Food Ingredients
Some ingredients are used in foods to increase their shelf-life.All are aimed either at controlling microbial growth or preventing fat rancidity.
Salt tends to reduce bacterial proliferation (Salted pork in the Revolutionary War).
Sodium Nitrite used in cured meats prevents Clostridium botulinum and is a great antioxidant.
Antioxidants are used to prevent fat rancidity.
Sodium lactate, paraben and other antimicrobial agents are used to control bacteria.
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41. Control of Water Activity
Water activity is a measurement of the water that is free to use by bacteria.
The goal of using water activity as a preservative method is controlling bacteria.
Beef jerky, cheeses and raisins are classical examples.
Honey and jellies are also good examples. Although they contain enough moisture to foster microbial proliferation, the water is bond by the high sugar content.
Bakery items and cereals have a very low moisture content and therefore do not spoil by bacteria.
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42. WATER ACTIVITY Aw/ Microorganism Foods 1.0-0.95 Bacteria
Yeasts
Molds
No microorganism
proliferation
Foods
Meat, fish, sausage, milk
Cheese, 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
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43. Control of pH pH is the degree of acidity. 7=neutral; Below 7 is acid.
Acid foods (below pH=4.6) do not foster spoilage or pathogenic bacterial growth.
Fermented items like sauerkraut, pepperoni, pickles, olives, and other acidified foods are good examples of this method of preservation.
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44. Packaging Packaging is a relatively new invention.
Packaging can range from a film overwrap (dust cover) to oxygen impermeable film to cans and jars.
In its simplest form, it acts as a dust cover to prevent the reintroduction of dirt, dust etc.
In its most complex form, the can, it acts also as a dust cover but also prevents the introduction of oxygen and it sturdy to take abuse and still maintain its function.
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45. Say nothing

46. Packaging
The advent of the oxygen impermeable film has dramatically increased the shelf life of foods from cured meats to potato chips. This film prevents oxygen from getting to the product hence reducing aerobic bacterial growth and retarding fat rancidity.
Some products are now packaged in a modified gas atmosphere usually containing nitrogen that is based on the exclusion of oxygen but also helps the food product from being crushed (e.g. potato chips).
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47. Say nothing

48. New Methods of Food Preservation
Irradiation is now being used to preserve some foods.
Spices generally have very high bacteria counts and are often irradiated to reduce the bacterial numbers.
Potatoes destined for long term storage are often irradiated to keep them from spouting.
Raw meats are now approved for irradiation mainly as a pasteurization method for the control of pathogenic bacteria.
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49. Food Preservation Combinations
Most foods that you buy use a combination of methods that we just discussed.
Let’s examine a few foods to see how they are preserved.
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50. Potato Chips
They are processed with salt (a pro-oxidant), cooked in oil, which gives them a high, unstable fat content. These factors will cause potato chips to go rancid rather quickly.
But potato chips are low in moisture and therefore not a good bacterial growth media in addition to being cooked which kills bacteria.
They have antioxidants in them to slow down rancidity.
They are packaged in an oxygen impermeable film with nitrogen gas atmosphere thereby preventing rancidity.
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51. Say nothing

52. Cured Meats
Meat items such as bologna, weiners and ham are high moisture, high fat/ high salt and cooked. Ideal for fat rancidity and bacterial growth.
But they are cooked which pasteurizes them.
They are refrigerated to retard bacterial growth
The salt which promotes fat rancidity also keeps down bacteria.
Nitrite (cure) prevents growth of some pathogens and also is one of the best antioxidants.
They are vacuum packaged for bacterial and rancidity control (based on the exclusion of oxygen).
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53. Say nothing

54. Canned/ Jars of Soups, Fruits and Vegetables
Most of them are heat sterilized to kill all bacteria.
When processed in the jar or can, oxygen is evacuated before sealing to prevent fat rancidity.
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55. Say nothing

56. Milk and Dairy Products
Most dairy products are pasteurized which is a heat-based treatment to reduce bacteria.
Sold as refrigerated item. Controls bacterial via cold methods.
Are usually packaged to remove oxygen to prevent fat rancidity.
Items such as cheeses have a low pH and water content for extended shelflife.
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57. Pasteurization of milk is required in most states
Pasteurization of milk is required in most states. Milk is pasteurized at 161F for 15 seconds.

58. Cereal and Bakery Items
Bacteria is not usually a problem because of low moisture content.
Fat rancidity is not a big problem because they are fairly low in fat and some antioxidants are usually added.
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59. Bakery items can foster mold but do not have the moisture content to foster bacterial growth.

60. Fresh Fruits and Vegetables
Shelf-life is usually several weeks.
Some fruits and vegetables are irradiated or packaged in modified gas atmospheres to control the ripening process and retard microbial growth.
Fat rancidity is not a problem-little or no fat.
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61. Say nothing

62. Say nothing

63. Conclusions
Food preservation has had a long history and has only more recently been scientifically understood.
An understanding of the fundamentals of food preservation and the conditions affecting bacterial growth (FAT TOM) has helped to develop newer and more technologically advance methods of food preservation.
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