Food Preservation Methods

Method	Advantages	Disadvantages
Drying (e.g. freeze-drying, spray-drying, sun-drying)	Produces concentrated form of food. Inhibits microbial growth & autolytic enzymes. Retains most nutrients.	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.
Smoking	Preserve partly by drying, partly by incorporation of substances from smoke.	Eating a lot of smoked foods has been linked with some cancers in some parts of the world.
Refrigeration	Slows microbial multiplication. Slows autolysis by enzymes	Slow loss of some nutrients with time
Freezing	Prevents microbial growth by low temperature & unavailability of water. Generally good retention of nutrients.	Blanching of vegetables prior to freezing causes loss of some B-Group vitamins and vitamin C. Unintended thawing can reduce product quality.
Adding salt or sugar	Makes water unavailable for microbial growth. Process does not destroy nutrients.	Increases salt and sugar content of food.
High heat processing (e.g. pasteurisation)	Inactivates autolytic enzymes Destroys microorganisms.	Loss of heat-sensitive nutrients.
Canning (involves high heat processing)	Destroys microorganisms & autolytic enzymes.	Water-soluble nutrients can be lost into liquid in can.
Chemical preservatives	Prevent microbial growth No loss of nutrient.	Some people are sensitive to some chemical preservatives.
Ionizing radiation	Sterilizes foods (such as spices) whose flavour would change with heating. Inhibits sprouting potatoes Extends shelf life of strawberries and mushrooms	Longer shelf life of fresh foods can lead to greater nutrient losses than if eaten sooner after harvesting.

Nutrient	Stability Characteristics
Vitamin A	Quite stable during processing and cooking
Vitamin D	Very stable to heat but sensitive to exposure to air and light.
Vitamin E	Relatively stable except at deep frying temperatures
Vitamin K	Stable in cooking but sensitive to light.
Thiamin	Quite unstable to heat and alkaline conditions. Lost during refining of cereals. Dissolves in cooking water.
Riboflavin	Very sensitive to light: 50% lost from milk left in sun for 2 hours. Relatively stable to most home cooking methods (unless bicarbonate of soda added).
Niacin	Stable to most processing but leaches into cooking water.
Vitamin B-6	Moderate retention during most processing.
Vitamin B-12	Moderate retention, but losses occur when heated under acid and alkaline conditions.
Folic acid	Large losses can occur during cooking. Presence of copper aids destruction.
Pantothenic acid	Relatively stable during most home processing.
Biotin	Good retention during most home processing.
Vitamin C	Unstable. Losses occur from exposure to air, light, heat and copper. Also dissolves in cooking water.

Do not store fresh foods for long periods - purchase just enough to last a week or less, and
eat soon after buying.

Store foods in a cool, dark place.

If slicing or chopping, keep the pieces as large as possible.

When boiling, add the raw food once the water is already boiling.

Use the smallest amount of cooking water possible.

Cook all foods for the shortest possible time. (Especially in the case of vegetables, lengthy cooking causes large losses of nutrients).

Do not use copper pots or utensils.

Do not use baking soda to preserve the colour of vegetables, as this increases vitamin losses.

Use cooking water and liquid from canned foods for gravies, sauces and soups.

Microwave cooking, because it is quick and avoids the use of cooking water in most instances, is a good way to save nutrients.