food preservation

PRINCIPLES OF FOOD PRESERVATION

Dr Vandana Mahajani

1

Importance of food preservation1 Elimination of microbes

2 Increasing shelf life of food

3 Making seasonal fruits available to them throughout the year

4 Adding variety to the diet

5 Saving time and energy

6 Improving nutritional value of foods

7 Controlling prices

2

All foods undergo deterioration/ spoilage after harvest to some degree

Role of food sciences is to minimize negative changes to the extent possible

3

Factors affecting microbial spoilage

Intrinsic factors (Factors related to the food itself)Extrinsic factors (Environmental conditions where the food is stored)

4

Intrinsic factors

.pH

.Moisture content

.Water activity

.Oxidation-reduction potential.Physical structure of the food.Available nutrients.Presence of antimicrobial agents

5

Extrinsic factors

.Temperature

.Relative humidity

.Gases (CO2, O2) present

.Types and numbers of microorganisms present in the food

6

Principles of food preservationPreventing entry of microbes can be done by1 Asepsis- packaging the food in cans or airtight

containers2 Filteration- used to filter liquids like juices water

and alcoholic beverages3 creating conditions by which the microbes in the

food do not grow like freezing, drying etc.

7

Microorganisms in Food

Water availability– in general, lower water activity inhibits microbial

growth– water activity lowered by:

• drying• addition of salt or sugar

– osmophilic microorganisms• prefer high osmotic pressure

– xerophilic microorganisms• prefer low water activity

8

Techniques of food preservation1. Physical preservation- heat and radiation are

used to control the growth of microbes

2. Chemical preservation- potassium meta bi sulphite and sodium benzoate , salt, sugar , lemon and vinegar are used to carry out chemical reaction in food to retard microbial action

3. Biological preservation- microbial growth is encouraged so as to carry out fermentation to preserve foods 9

Microorganisms in Food

Antimicrobial substances– coumarins – fruits and vegetables– lysozyme – cow’s milk and eggs– aldehydic and phenolic compounds –

herbs and spices– allicin – garlic– polyphenols – green and black teas

10

Extrinsic Factors

temperature– lower temperatures retard microbial growth

relative humidity– higher levels promote microbial growth

atmosphere– oxygen promotes growth– modified atmosphere packaging (MAP)

• use of shrink wrap and vacuum technologies to package food in controlled atmospheres

11

Methods of Food Preservation

Heat

most bacteria are killed at 82-93oC, but spores are not

121oC wet heat for 15 minutes is required to ensure sterility

high acid foods require less heat

in milk, only disease-causing organisms are killed to reduce the severity of heat required 12

Pasteurization– kills pathogens and substantially reduces

number of spoilage organisms– different pasteurization procedures heat for

different lengths of time– shorter heating times result in improved

flavor

13

Canning: more than 400 foods preserved by canning

food heated in special containers (retorts) to 115 °C for 25 to 100 minutes

kills spoilage microbes, but not necessarily all microbes in food

14

Syrups and Brine

Helps fill spaces between canned foods and adds flavour to foods.

Principle sugars used are sucrose and dextorse

Dilute salt solution with 1-2% salt is used in canneries for vegetables

15

Spoilage of canned goods

spoilage prior to canning

underprocessing leakage of

contaminated water into cans during cooling process

16

Blanching

Hot water or steam scald is given.

Drives out gases and surface material

17

Preservation Techniques…...

Cold

under 10oC, microbial growth is slow

frozen food (<-10oC) usually does not have any free water

frozen food also benefits from low water activity to help protect against microbial growth

freezing may kill some, but not all microorganisms, but growth is slowed or stopped

18

Food Preservation

Low Temperature– refrigeration at 5°C retards but does not

stop microbial growth– microorganisms can still cause spoilage

with extended spoilage– growth at temperatures below -10°C has

been observed– Food should not be re-frozen after thawing

19

Preservation Techniques…...Drying

dehydrating food also dehydrates the microorganisms which contain approx. 80% moisture

Mostly used for meat, however fruits and vegetables also dried.

Cutting veg, blanching or scalding( inactivates the enzymes), drying ( steam, air , vaccum or inert gas) and packing.

Onions and garlic not blanched

20


Sugar & Salt

Addition of either to a food item increases the affinity of the food for water, thereby removing water from the microorganism through osmosis

21


Acidification

acids may be in foods naturally, produced by fermentation, or added artificially

as pH decreases, heat required for sterilization is reduced

Lactic acid fermentation used in preparation of cheese ripening, corn, pickles, peas, beans, olives

22


Smoke

Contains formaldehyde and other preservatives

Heat will help reduce microbial populations and somewhat dries the food

23


Atmosphere

Exclude air (O2) for control of aerobes

Provide air (O2) for control of anaerobes

Add CO2

Add N2

24

Food Preservation

Removal of Microorganisms– usually achieved by filtration– commonly used for water, beer, wine,

juices, soft drinks, and other liquids

25

Chemical preservatives

Propionates of calcium and sodium Added to dough to prevent growth of

mould and increase shelf life of food Sorbates potassium salt of sorbic acids

added to acidic food to control growth of fungi or yeasts in apple juice. Wrappers of cheese also made of this.

26

Benzoates used to preserve acid products just like sorbates

Citric, lactic, acetic and phosphoric acids. They are used a s acidulants in food . Acetic acid and lactic acids have the greatest preserving power

Sodium chloride salt is added to presrve meats specially

27

Food Irrdaiation One of the beneficial applications of

atomic energy It involves controlled application of

energy from gamma rays, X rays, and accelerated electrons

Low doses (.15 kilo Gray) can prevent sprouting of potatoes and onions

28

Methods of preservationAdvantages

1. DryingConcentrated form of foodInhibits microbesRetains nutrients

2. SmokingPartly by drying and partly by incorporation of certain substances

3 RefrigerationSlows microbial actionSlows action of enzymes

4 FreezingPrevents microbial growth and availability of waterGood retention of nutrients

5. Adding salt and sugarMakes water unavailableDoes not destroy nutrientsHelps in preservation

Disadvantages

Loss of thaimine and Vit CSO2 is added to retain some nutrients , but some individuals may be sensitive to these.

Eating smoked is liked with some cancers in some parts of the world

Slow loss of some nutrients with time

Blanching of veges prior to freezing may cause loss of Vit B and C

Increases salt and sugar content of the food

29

Advantages

6. High heat processingEg. PasteurisationDeactivates enzymesDestroys micro organisms

7. CanningDestroys microbes and enzymes

8. Chemical preservativesPrevent microbial growthNo loss of nutrients

9. Ionising radiationSteralizes food without changing flavours like spicies.Inhibits sprouting of potatoesIncreases life of food like strawberries and mushrooms

Disadvantages

Loss of hest sensitive nutrients

Water soluble Vitamins may be lost due to liquid present in the can used for preservation

Some people are sensitive to some preservatives

Longer shelf life of foodsCan lead to greater loss of nutrients

30