Food preservation

Common methods of preserving food in our homes to save it from the attack of microorganisms are:

• Chemical Method: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore, they are called preservatives. Salt or acid preservatives are added to pickles to prevent the attack of microbes.
• Preservation by Common Salt: Meat and fish are covered with common salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
• Preservation by Sugar: Jams, jellies, and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria that spoil food.
• Preservation by Oil and Vinegar: The use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish, and meat are often preserved by this method.
• Heat and Cold Treatments: The process of heating milk to about 700C for 15 to 30 seconds and then suddenly chilling and storing it is called Pasteurization. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur.
• Storage and Packing: These days, dry fruits and even vegetables are sold in sealed air-tight packets to prevent the attack of microbes.

NCERT Notes for Class 8 Science Chapter-2: Microorganisms: Friend and Foe: Organisms that can be seen only through a microscope are known as Microorganisms or Microbes. These microorganisms are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes. They exist in vast numbers and play vital roles in our lives.

Friends and Foe explain that Microorganisms can be both our friends, providing numerous benefits, or our foes, causing harm and disease. Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa, and some algae. Viruses are also microscopic but are different from other microorganisms. Common ailments like colds, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses. Diseases like dysentery and malaria are caused by protozoa(protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.