Theory:

Food preservation
 
Salts and oil are some of the common items used to control the growth of microorganisms. Have you ever wondered why pickles have so much of oil? This is because pickles will be stored for a longer period of time. To protect it from the growth of microorganisms, the higher quantity of oil is used as a preservative. 
  
Chemicals like Sodium benzoate and sodium metabisulfite are also commonly used preservatives.
  
Some preservatives used as ingredients
  • Common salt
  • Oil
  • Sugar
  • Vinegar
  
Common salt is added in food products such as pickles, and also fresh meat and fish are covered with dry salt rocks to prevent the growth of bacteria, hence acting as a preservative.
 
Excessive use of oil in pickles can save pickles from getting spoiled from fungal and bacterial growth since they will be stored for a longer period of time. This process is known as pickling.
 
In jams and squashes, sugar used as an ingredient also acts as a preservative so that it can be stored for a longer time.
 
Vinegar is also used in pickles to ensure the pickle can be used for a longer period of time, it can be used as a preservative or to protect the product from microbe growth. This is known as chemical pickling.
 
salt-3285024_1920.jpg     oil-4991420_1920.jpg     sugar-1920.jpg   
  
Pasteurisation
The process of boiling milk to a temperature of around \(70°\)Celsius for about \(15\) to \(30\)  seconds and then chilled and stored before consuming is called Pasteurisation.
 
Milk packets have pasteurised milk, which every manufacturing company has to ensure so that milk is free from microbes.
  
Ways to avoid the growth of microorganisms
We store vegetables and fruits at a lower temperature (refrigerator) to reduce the growth of microorganisms. Even storing them in sealed airtight packets can reduce the growth of microbes.
 
Microbes in food processing
Fermentation is the process which produces alcohol, organic acids and esters. Many microbes are used in the process of fermentation. In fermentation, the microbes convert the sugar or starch to alcohol. Fermentation makes the dough softer and adds specific taste to breads.
  
Probiotics
Probiotic is a method of taking in live bacteria to cure certain diseases through milk or yoghurt. For example, bacteria such as Lactobacillus acidophilus and Bifidobacterium bifidum  if taken as a probiotic help improve digestion and absorption process in the gut.