Canning

Today we are canning pears using the Boiling Water Canner method. Canning preserves foods by heating them to high temperatures.In the canning process,oxygen is driven out and a vacuum is formed.Boiling water temperature kills most food spoilage and food-borne illness microorganism.

The advantages and disadvantages are as below. 

Advantage

• Destroys microorganisms & autolytic enzymes.

Disadvantage

• Water-soluble nutrients can be lost into liquid in can.

Drying

Drying is removal water from the food in order to expend the shelf life of food. The process is undergone with the aid of sunlight, wind or machines. 

The advantages and disadvantages are as follow .
ADVANTAGE

• Produces concentrated form of food. 
• Inhibits microbial growth & autolytic enzymes
• Retains most nutrients. 

DISADVANTAGE

• Can cause loss of some nutrients, particularly thiamin & vitamin C.
• Sulphur dioxide is sometimes added to dried fruits to retain vitamin C, but some individuals are sensitive to this substance.

Examples,

                               

Pickling

Pickling preserves food by adding vinegar.Pickling leaves the food with a higher  level of acid,making it an inhospitable environment for spoilage microorganisms.Food preserves by pickling are cucumber,ginger and so on .

The advantages and disadvantages are as follow

Advantages

• Pickling make food to last longer.
• Bacteria and fungi cannot grow in at very acidic medium.
• Pickling keeps thing fresh.

Disadvantages

• Pickling can change taste of food and destroyed the nutrient of food.
• Pickling which means there's a lot of salt content. Salt is bad for human health.
• Increases salt and sugar content of food. 

                                       

Pasteurisation

Pasteurization means heating liquid, particularly milk is heated to 65˚C for half an hour. Rapidly cooling it,and then storing it at a temperature below 10˚C .

The advantages and disadvantages are as below.

Advantage

• Heating at such high enough temperature kills most bacteria.However, it does not affect the taste and nutritional value of the food.
• Pasteurized to make milk, yoghurt drink and juices last longer.
• Inactivates autolytic enzymes.
• Destroys microorganisms

Disadvantage

• Increasing evidence of heat resistant organisms developing, its complicated process requiring mechanisation, and it can affect the taste pasteurised milk isn't that nice.
• Loss of heat-sensitive nutrients.

Waxing

A layer of coating such as wax is applied on some fruits and vegetables. Waxing of fruit and vegetables is also common. It prevents moisture loss and enhances the appearances of the fruits and vegetables. Waxed fruit need to be washed thoroughly or peeled before eating.

The advantages and disadvantages are as follow

Advantage

• Prevent moisture loss.
• Improve appearance.
• Reduce the susceptibility to Chilling  Injury.
• Decrease the rate of transpiration.
• Prevent other phsical damage.

Disadvantage

• Artificial appearance.
• Added cost.
• Surface burn.
• Wax whiting(chalking).
• Off-flavor development.

                                

Vacuum Packing

Vacuum – packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, slowing spoiling. Vacuum-packing is  commonly used for storing nuts to reduce loss of flavor from oxidation. Process that the food is sealed in a pack after air has been expelled.

The advantages and disadvantages are as fellow

Advantage

• Removing oxygen from the packaging is a main advantage to vacuum packing. Without oxygen the food will last much longer because the bacteria can't  "do their thing."

Disadvantage

• Buying a vacuum packaging machine can be expensive.
  
  
  
  

Freezing

People of  long ago also discovered that  freezing food could also mean it  could be kept for a long time .Freezing slows down the spoilage process by changing water into ice which is a form the bacteria cannot use. Freezing food is the easiest ,most convenient,and the least time consuming method of preserving food.

The advantages and disadvantages are as below.

Advantage

• Prevents microbial growth by low temperature & unavailability of water. 
• Generally good retention of nutrients.

Disadvantage

• Blanching of vegetables prior to freezing causes loss of some B-Group vitamins and vitamin C. 
• Unintended thawing can reduce product quality. 

Smoking

Another tradisional way of preserving food is to smoke it. It is often use for fish. The fish is hung inside a building and a smoky fire is lit below.Other preservation mechanisms of smoking are heat and surface dehydration.

The advantages and disadvantages are as below.

Advantage

• Preserve partly by drying, partly by incorporation of substances from smoke

Disadvantage

• Eating a lot of smoked foods has been linked with some cancers in some parts of the world.