Food preservation ,any number of methods by which food is kept from spoilage after harvest. Such practices date to prehistoric times . Among the oldest methods of preservations are drying ,refrigeration , & fermentation. Modern methods inclues canning, pasteurization ,freezing, irradiation, & the addition of chemicals. Advances in packaging marterials have played an important role in modern food preservation .

1. Mahatma Jyotiba Phule Rohilkhand University
Bareilly
2023-24
“ FOOD PRESERVATION METHODS AND FOOD SAFETY
ISSUES”
Food Microbiology
by
Ms Ayushi
Sharma
Faculty of
microbiology

2. INTRODUCTION
 Food preservation ,any number of methods by which food is kept from
spoilage after harvest. Such practices date to prehistoric times .
 Among the oldest methods of preservations are drying ,refrigeration , &
fermentation.
 Modern methods inclues canning, pasteurization ,freezing, irradiation, & the
addition of chemicals.
 Advances in packaging marterials have played an important role in modern
food preservation .

3. METHODS OF FOOD PRESERVATION
 Food preservation methods can be classified as follows:
A. PHYSICAL METHODS
1. Preservation by low temperature
 Refrigeration
 Freezing
2. Preservation by high temperature
 Pasteurization
 Canning
3. Preservation by drying
 Sun drying
 Drying by Mechanical driers
4 Preservation by Irradiation
B. CHEMICAL METHODS
 High concentration of salt.
 High concentration of sugar.
 Using chemical preservativess

4. PHYSICAL METHODS
1.Refrigeration: The temperature maintained in the refrigerator is 0 to 5
degree celcius
 Enzymatic & microbial changes in foods are slowed down considerably.
 Perishable foods like eggs, dairy products, meat, sea foods, fruits and
vegetables are stored in refrigerator .
 Food can be stored safely for few days or week.
2.Freezing: The temperature of freezer is -18 to -40 degree celcius .
 Microbial growth is prevented completely & the action of food enzymes
greatly reduced .
 Frozen foods have better quality & needs uninterrupted supply of
electricity while storing.
 Foods like Poultry ,Meat, Fish ,Peas, Vegetables ,Juice concentrates can
be preserved for several months by this method.

5. 3.Preservation by High Temperature
 Pasteurization: It is a mild heat treatment that kills a part but not all the microorganism present &
usually involves the application of temperature below 100 degree celcius.
 Canning: Canning is the processs in which the foods are heated in hermetically sealed (airtight) jars or cans
to a temperature that destroys microbes & inactivates enzymes that can cause food spoilage.
 The general steps to be adopted for canning foods are cleaning, balancing , filling, exhausting, sealing,
sterilizing ,cooling and labelling.

6. PASTEURIZATION

7. 4.Preservation by Drying
Microorganisms need moisture to grow. When exposed to sunlight or Subjected to dehydration , the
moisture in the food is removed & the concentration of water is brought below a certain level. This
prevents the growth of microbes and thereby spoilage of food.
 Sun Drying: It is limited to regions with hot climates & dry atmosphere & to certain
fruits such as raisins , figs, apricots, pears, and peaches.
 It is a slow process.
 Drying by Mechanical Driers : Artificial drying involves the passage of hot air with
controlled relative humidity over the food to be dried or the passage of the food
through air, fruit, vegetables, nuts , fish, & meat can be preserved by ths method.
 In the dehydration process , artificial drying methods like spray drying, vacuum drying,
drum drying and freeze drying are used for drying foods.

8. 5.Preservation by Irradiation
Food irradiation also called as Cold Sterilization.
The Foods are bombarded by high energy rays called
Gamma rays or by fast moving electrons to kill bacteria , fungi
and insects & in some cases to delay fruit ripening or prevent
sprouting in onions & potatoes .
The goal of irradiation is to kill the microorganism & inactivate
the enzymes without altering the food.

9. CHEMICAL METHODS
I. High concentration of Salts
 It is an ancient preservation technique .
 Food is treated with salt or strong salt solution .
 Salt causes high osmatic pressure & shrinking of cell ,
dehydrates foods and microbes by drawing out moisture.
II. High Concentration of Sugar
 Sugar has the ability to bind water & make it unavailable for
microbial growth.
 It reduces the solubility of oxygen in moisture , which is
essential for the growth & multiplication of microbes.
 Apples, Oranges, Guava, Grapes, and pineapples are
suitable for making jams and jellies.

10. III. Using Chemical Preservatives
 The chemicals when added interfere with cell membrane of microorganism ,their
enzyme activity or their genetic mechanisms.
 They also act as antioxidants.
 The common chemical preservatives permitted are :-
a. Benzoic acid(including benzoates): Sodium benzoate is a salt of benzoic acid & is
used in preservation of coloured fruit juices and squaches.
b. Sulphur di oxide (including sulphites): Potassium metabisulphite is used as a source
of sulphur dioxide when it is added to the juice or squash . When used in fruits with
deep colors like blue grapes , jamun, watermelon, it bleaches the colour & hence in
such cases benzoic acid is desirable.
c. Organic acids and their Salts: Foods can be preserved by adding lactic,acetic,
propionic, citric acids & their salts . Nitrates and nitrite compounds are used to
preserved meat and fish products ,it gives desirable colour, flavour & discourages the
growth of microbes .It also prevents toxin formation by microorganism in food.

11.  Food safety is the scientific method of handling, and storing food
to prevent food borne illness .
 It includes:-
 Food contamination: Food can become contaminated with
bacteria, viruses, parasites, chemical agents , & toxins at any
stage, from production to contamination.
 Foodborne illness: It can be caused by germs such as
Salmonella, Botulism, Cryptosporidium, Cyclospora , Hepatitis A
virus, Shigella & Yersinia etc.
 Some common cause of foodborne illness includes;
 Improper cooling or heating of perishable foods
 Improper cooking temperature
 Dirty or contaminated utensils & equipment
 Poor employee health and hygiene
 Food from unsafe sources.