Food Preservation

university of duhokCollege of veterinary medicine

Food preservation by:mohammad abid

Special thanks to my spervisor: Dr. nechirvan ghafar

Introduction

Food Preservation, processes involved in protecting food against microbes and other spoilage agents to permit its further5 consumption. The preserved food should retain

a palatable appearance, flavor, and texture, as well as its original nutritional value.

The aim of food preservation is to minimize the growth of microorganisms during the storage period, thus

promoting longer shelf life and reduced hazard from eating the food.like,(Animal products).

Food Preservation in History

Nicolas appert(1749-1891)

Principles of preservations

killing of micro-organisms. Inhibition of microbial growth. Removing micro-organisms. Destroying enzyme.

Retardation of chemical changes

Conditions for the growth of micro-organisms

conditions

pH value

oxygen moisture

Microbial Growth

Time and temperature

Methods of the preservation and their side effects

1.Heat treatment2.Irradiation3.Smoking4.Drying and dehydration5.Refrigeration6.Freezing7.Canning8.Sugaring and Salting9.Meat curing10.Pickling in vinegar11.Use of food additives12.Filtration

1.Heat treatment

Principle Food is heated up and cooked. Kills the microorganisms and their spores alters protein structures destroys enzyme activity of microorganisms

Methods of heating1.Blanching2.sterilization3.commercial sterilization4.Pasteurization Levels of pasteurization used to thermally process milk

include:(1) Low Temperature Long Time (LTLT): 63° C (145° F) for 30 min(2) High Temperature Short Time (HTST): 72° C(161° F) for 15 s

(LTLT and HTST are equivalent thermal processes)(3) Ultra High Temperature (UHT): 138° C (280 ° F) (or higher) for

2 s

• Advantage: Inactivates autolysis enzymes. Destroys microorganisms.

• Disadvantage: High temperatures can diminish product

appearance,texture, and nutrient quality.

• Examples: All forms of cooked food, milk sterilized by UHT (ultra high

temperature).

2.Irradiation

Principle Exposing food to ionizing radiation is to destroy enzymes

and micro-organisms in food; kill mould and destroy bacteria in fresh meats.

Irradiated foods are not radioactive Type of radiation used for food preservation is ionizing

radiation.

Advantage: less Nutritional losses The chemical reactions associated with food irradiation do, in

fact, produce very small amounts of new compounds called radiolysis products.

Disadvantage If irradiated food becomes contaminated, new pathogens

have little competition and can multiply more rapidly.

The energy used for irradiated food are: 1.Gamma rays 2.X-rays 3.Electrons (Radura)

3. Smoking Principle The smoke is obtained by burning special type of wood

under low breeze/wind at about 93oC to 104oC. Woods used for smoking are Alder, apple and cherry, hickory,

maple, mesquite, oak, pecan.

Smoking process

Disadvantage smoked foods are carcinogenic.

Examples: Fish (Smoked salmon), ham, and sausage

Smoked ham Smoked sausage

4. Drying and Dehydration

Principle Drying removes the moisture from the food so that bacteria,

yeasts and moulds cannot grow and spoil the food. It also slows down the action of enzymes, but does not inactivate them.

Drying methodsAir

OvenMicrowave oven

Preservation processNormal loss of nutrition Processing method

Canning 60-80% high temperatures

Freezing 40-60% water-logging and rupturing of cells

Dehydrating 5-15% moderate heat and moderate air flow

In-home Drying 3-5% low heat and gentle air flow

DisadvantageDisadvantage Time Time and and workwork, including rehydrating of the food before , including rehydrating of the food before eating.eating.AdvantageAdvantage Drying food loss only a little nutrition Drying food loss only a little nutrition in the food.in the food.

5. Refrigeration Principle process of lowering the temperature and maintaining it in

a given space for the purpose of chilling foods ,Chilling slows down microbial activities and chemical changes resulting in spoilage.

In chilling, food is kept at 0oC - 4oC.

Disadvantage: food cannot be stored for long time.

6. Freezing

Principle It converts water of the food to ice, so the water is

unavailable for metabolic reaction of the microorganisms. In freezing, food temperature is reduced to about -17oC.(Freezer).

Chemical changes during freezing

Enzymes are proteins present in plants and animal. Even after we harvest plants or slaughter animals, enzyme reactions can continue and result in undesirable color, flavor and texture changes in the food. Freezing slows down, but does not destroy enzymes. The two methods you can use are blanching and adding chemical compounds such as ascorbic acid.

Changes in food texture during freezing

• Freezing involves the change of water contained in the food from a liquid to a solid (ice). When water freezes it expands, and the ice crystals formed cause cell walls of food to rupture. As a result, the texture of the product will be much softer when it thaws.

• Disadvantage Freezing would cause low temperature injury.

Examples: Frozen meat, peas, vegetables, ice-cream

7. Canning

Principle Preserving food by heating and sealing in airtight

containers

• Advantage

The steel can recycle process

• Disadvantage

Food are not thoroughly heated or the containers are not properly canned may lead to growth of clostridium botulinum or spoilage of canned food.

Examples: All kinds of tinned foods, such as soup, meat, beans

Canned food

8.Sugaring and Salting

Principle Food is treated with strong salt solution or strong sugar

solution. Disadvantage The food may become very salty or very sweet.• Examples: Bacon, salted fish

9.Meat curing

Principle Meat is treated with salt or strong salt solution containing

NaNO3, KNO3 and which may contain sugar and spices. Salt and sugar both cure meat by osmosis. In addition to

drawing the water from the food, they dehydrate and kill the bacteria that make food spoil.

Nitrite or nitrate are used for retarding rancidity, curing-pink color, killing bacterial

Two curing methods 1. Wet (or brine) curing 2. Dry curing In the wet curing, the curing ingredients were mixed with boiling

water to form”pickling" brine. But in dry curing, the ingredients were simply rubbed into the meat several times over the period of the cure.

• Disadvantage fall in the level of hemoglobin in the blood Malnutrition and reduced lifespan. Nitrates are harmless, but when nitrates are ingested in the diet

they are reduced to nitrites in the body. Then nitrites may react to form nitrosamines.

Nitrosamines are carcinogenic.

• Examples: Salted fish, pork shoulder, ham, corned beef, bacon.

Pork shoulder

10.Pickling in vinegar Principle Food is kept in vinegar since micro-organisms can not

grow well in low pH value solutions. Disadvantage Vinegar is a temporary preservative, because enzymes

continue to act, softening and spoiling the product. Some kind of vinegar such as apple cider vinegar will darken

most vegetables and fruits. Examples: Sauces, pickled onions and cucumbers (no animal

products)

11.Use of food additives

Principle Food Additives, natural and synthetic compounds added to

food to supply nutrients, to enhance color, flavor, or texture, and to prevent or delay spoilage. Some additives can inactivates or kill micro-organisms, retard chemical spoilage.

Types of additives Natural additives

Artificial additives

Functions of food additives Preserve food Do not preserve food • E-number It is the reference number of food additives

The E Number List

• Disadvantage allergic reactions. hyperactivity or asthmatic symptoms especially in children

and young people. certain reactions.

12.Filtration

Principle Filtration can remove microorganisms from the liquid,this

method is used for clearing fluids.