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SAI International School
                                            Subject- Biology, Class-VIII
                                    Topic- Microorganisms: Friend and Foe
                                           Subtopic- Food Preservation
                                                       Module- 16

                                                     Lesson Notes

               Food preservation: Food gets spoiled due to growth of microorganisms. Spoiled food
               has  bad  smell,  bad  taste,  colour  change  and  moreover,is  harmful  for  humans  and
               animals. Spoiling of food involves biochemical reactions.


               Food  preservation  is  important  because  food  can  be  stored  for  longer  period  without
               getting  spoiled.  Surplus  food  can  be  stored  for  future  use.The  substances  used  to
               prevent the growth of microorganisms are called preservatives.

               Methods of Preservation:

               Chemical  method:  Sodium  benzoate  and  sodium  metabisulphiteare  used  in  jams,
               squashes to prevent spoilage.

               Preservation  by  common  salt: Meat and fish are preserved by adding common salt
               which prevents the growth of bacteria. Salting is done to preserve raw mangoes, Amla
               and Tamarind.

               Preservation by sugar: Sugar reduces the moisture content and reduces the growth of
               bacteria. In Jam, Jelly and squashes, sugar is added.


               Preservation  by  oil  and  vinegar: Bacteria cannot live in oil and vinegar.  In pickles,
               fish, fruits and vegetables, oil and vinegar are added.

               Heat  and  cold  treatment:  In  this  method,  milk  is  boiled,  cooled  and  stored  in
               refrigerator. Microorganisms are killed by heating and low temperature in storing places
               like refrigerator inhibits their growth.

               The milk available in packets is pasteurized milk. Pasteurisation is a process in which
               milk is heated up to 70 degree Celsius for 15 to 30 seconds and suddenly chilled and
               stored.  It  kills  the  microbes  and  prevents  their  further  growth.Pasteurisation  was  first
               discovered by Louis Pasteur.

               Storage and packing: In this method, dry-fruits, vegetables,fruits and snacks items are
               packed in air-tight packets to prevent the growth of microbes.
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