Food Preservation

Food Preservation

Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness and extend its shelf-life while keeping as much of its nutritional quality

Food processing

Food processing is the set of methods and techniques used to transform raw ingredients into food for consumption.

Examples of food processing methods include:








Types of Food Preservation

Food processing methods that are used to preserve foods include:

Refrigeration and freezing





Fermentation: microbial decompostion resulting in alcohols, vinegar, lactic acid (kraut)(pickles)

Chemicals: salt, sugar, vinegar

Food Deterioration & Spoilage

Food deterioration is any change in food that makes it less desirable. (flavor, color, texture & smell)

Food spoilage is the state of food where it is no longer safe to consume.

How does food start to spoil?

Once food is harvested or slaughtered, its plant or animal tissue soon starts to decay.

What are the micro-organisms?





Molds are microscopic fungi that can form visible colonies.


Yeasts are microscopic fungi but rarely grow on foods.


Bacteria are microscopic organisms that can both spoil food and produce toxins causing food-borne illness

Enzymes & Chemical Reactions

Enzymes help facilitate chemical reactions that cause foods to spoil.

As Chemicals in food are altered, the smell, appearance, texture and flavor can change.

Oxidation of apples and potatoes when sliced; In apples, the specific enzyme that causes the brownish colour to appear is called polyphenol oxidase (PPO).

Signs of Spoilage


Brown meats

Sour milk

Mushy Vegetables



When in doubt, throw it out.

What is a food-borne illness?

A food-borne illness is derived from food. Majority of these illnesses are caused by micro-organisms which are called Pathogens.

Pathogens are bacteria that cause disease. (ex. E.coli H7,Salmonella)

E.Coli H7

Causes diarrheal problems which can cause complications that sometimes lead to death.


Causes gastroenteritis infections

Clostridium botulinum

Clostridium botulinum is a Gram-positive, rod shaped bacterium that produces the neurotoxin botulin, which causes the flaccid muscular paralysis

Food preservation

So, how does food preservation work?

All of the food preservation processes work by slowing down the activity and growth of disease causing bacteria, or by killing the bacteria all together.  They also slow down or stop the action of enzymes which can degrade the quality of the food.


Water Activity


How does food preservation help?

The goal of food preservation is to minimize the activity of micro-organisms (pathogens), enzymes and chemical reactions.

This will help keep the food free from spoilage and illness-causing micro-organisms.

Freezing is the unit operation in which the temperature of a food is reduced below its freezing point and a proportion of the water undergoes a change in state to form ice crystals. The immobilization of water to ice and the resulting concentration of dissolved solutes in unfrozen water lower the water activity (aw) of the food

Preservation is achieved by a combination of low temperatures, reduced water activity and, in some foods, pre-treatment by blanching

Introduction to Food Preservation Methods.
High-Temperature Systems

Basically, two different food preservation categories are performed with heat application:

Pasteurisation and sterilisation

Pasteurisation is defined which is able to destroy pathogenic life forms, and the most part of those vegetative microorganisms in foods ; moreover, enzymes are reported to be inactivated with pasteurisation treatments

Sterilization is defined as the destruction of all microbial forms, including spores.

A) Indirect method. In detail energy is supplied by means of an indirect steam injection system; fluids are forced to pass through close heat exchanger

B) Direct system. The preheated food and the injected heating medium (steam) are in direct contact for a few seconds; subsequently, under-vacuum cooling is required, similarly to pasteurisation treatments, with the aim of eliminating extra water (a certain volumetric augment is observed in the process).

Cold Preservation

The cold slows down until it stops degradative (chemical and enzymatic) reactions inside the food. This effect is mainly due to the inhibition of microbial activity

enzymes: they are not denatured and therefore inactivated, but their action is inhibited (rendered useless) in relation to the low temperature of the food.

Moreover, the inhibitory action of low temperatures occurs with the subtraction of free water from the system because of ice formation with the consequent increase in the concentration of extracellular solutions and the dehydration of microbial cells.

There are two different methods of food preservation by cold storage refrigeration and freezing systems. The first method, refrigeration preservation, concerns the storage of food commodities at temperatures low enough to slow down degradative (chemical and enzymatic) reactions inside stored products; in addition, water must remain liquid.


The term ‘dehydration’ means the progressive reduction of water content inside foods with the aim of inhibiting microbial spoilage; essentially, this process has microbiostatic effects. However, three different processes can be named ‘dehydration’:

a) Concentration

b) Drying

c) Freeze-drying.


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