food preservation Flashcards
STERILIZATION
Is defined as the complete destruction of microorganisms by applying heat.
PECTIN
This is a Gelatin- like carbohydrate obtained from certain under- ripe fruits used to thicken jams and jellies.
BLANCHING
May be defined as a cooking process where the food usually vegetables is scalded in boiling water, removed after a brief time interval and finally plunged into ice cold water or placed under cold running water.
The Purpose of Blanching is To
Loosen peels from vegetables
To remove undesirable flavours or
To prepare vegetables for freezing
REASONS FOR PRESERVING FOODS
The main reason for preservation is to prolong the shelf life of food.
To make food available when they are out of season.
To make a variety of food available all year round as to prevent nutritional imbalance.
Convenience, frozen and canned foods are quickly and easily prepared.
To prevent waste by making use of food when they are plentiful and cheap and storing them for later use.
Principles on Which Methods Of Food Preservation Are Based
All methods used for preserving foods are based on the general principles of preventing the cause of spoilage.
The growth of microorganisms must be terminated. This can be achieved by removing some of the conditions necessary for their growth.
The following scientific principles form the basis of all methods of preservation.
REMOVAL OF MOISTURE:
This can be done by applying heat and allowing the water to evaporate.
Adding sugar or salt has the same effect.
Since the sugar or salt is more concentrated than the solution inside the cell, water passes out of the cell through the process of osmosis, and is replaced by the sugar or salt solution.
Then the cell becomes dehydrated.
Altering The Temperature:
Either increasing or decreasing the temperature can prevent microbial growth.
Refrigeration or Chilling: 32-40 F
Freezing 0 F or (18 C)Altering the PH :
The PH of the food may be lowered so that the food environment too acidic for microorganisms to grow.Exclusion of Oxygen:
This prevents only the growth of moulds and aerobic bacteria.
This method can only be successful if it is used with another method such as heating as in canning or even freezing.
Use Of Chemical:
A number of chemical can be used to terminate the growth of microorganisms. They are:
Antioxidants
Sodium chloride ( Common Salt)
Acid ( citric acid, vinegar)
Sulphur dioxide
SugarIrradiation:
This is one of the most recent methods used to reduce food borne- pathogens and extend the shelf life of foods.
METHODS OF PRESERVATION
There are different methods of destroying of the action enzymes and microorganisms in food.
Heat preservation
Dehydration
Cold preservation (Refrigerating and Freezing)
Addition of Chemical preservatives
Removal of air through packing
HEAT PRESERVATION
STERILIZATION
PASTEURIZATION
CANNING AND BOTTLINGPASTEURIZATION:
This involves heating items such as milk below its boiling points but at a temperature sufficient to pathogenic organisms.
Example of Products Included:
Milk and milk products, fruit juices, wine, Beer, Vegetable juices.
STERILIZATION:
Foods, especially milk is heated in sealed containers at a high temperature.
CANNING AND BOTTLING:
These are based on the principles that food is sealed in a can or bottle and then heating to such a temperature that all harmful microorganisms capable of growth during storage of the can or bottle at normal temperatures are killed.
DEHYDRATION
Dehydration, in food processing, means by which many types of food can be preserved for indefinite periods by extracting the moisture, thereby inhibiting the growth of microorganisms
REFRIGERATION AND FREEZING
Lowering the temperature prevent microorganisms from multiplying and reducing enzymes activity.
In a domestic refrigerator food should remain at a temperature of (5 degrees celsius).
The domestic freezer will freeze foods for safe storage at (-18 degrees celsius) or (0 degrees fahrenheit).
Most microbial growth is halted at (10 degrees fahrenheit) but once defrosted the growth of ,microorganisms begins again.
