What is Pasteurization?

Pasteurization is a heat treatment food preservation method that kills a part of the microorganisms present in the food. Therefore, this technique is used for foods that can be stored and further handled under suppressed microbial growth conditions. Owing to the low heat treatment process, the nature of the food would not change; thus it would preserve the nutrient value of the food.

In the pasteurization process, usually a liquid is heated to a specific temperature for a predefined time period followed by immediately cooling step (E.g. 63-66 °C for 30 minutes or 71°C for 15 seconds).  This was first invented by a French chemist and microbiologist, Louis Pasteur.  This technique was first used to prevent souring of wine and beer, but lately milk was also pasteurized using this technique. Presently, this method is being widely used to extend the shelf life of milk.

The prime objective of pasteurization is to remove or destroy pathogenic bacteria and microorganism, and not to destroy heat resistant spores entirely as the employing temperatures are not very high in the process. It is also targeted to suppress the activity of a particular micro-organism in particular foods. Therefore, it does not give a safe shelf stable product without proper storage at low temperatures.

The second objective is to reduce the enzymatic activities in the product. Pasteurization depends on the heat resistance of the particular microorganism and the heat sensitivity of the product. The two main methods of pasteurization are high-temperature, short-time (HTST) and Low-temperature, long time or Extended Shelf Life treatment (ESL).

What is Sterilization?

Sterilization is another form of thermal processing technique which uses comparatively high temperatures to extend the shelf life by a few months. Since the bacterial spores are far more heat resistant than the vegetative cells, the main objective of this technique is to destroy their spores. Commercial sterilization depends on many factors, including the nature of food, storage conditions of the food following the thermal process, heat resistance of the microorganisms or spores and initial amount of microorganisms present in the food.

Sterilization process can be divided into two main categories. First one is ‘in-container’, which is used for foods, which are placed in containers such as cans, bottles and plastic pouches. Second one is ‘Continuous flow system for ultra high treatment (UTH) processes, which generally involves heating at 140 °C to 150 °C for 1 to 3 seconds.

What is the differences between Pasteurization and Sterilization?

  • Sterilized products have a long shelf life than pasteurized products.
  • Generally sterilization involves heating of food between 110° C to 120 ° C temperature ranges while pasteurization involves heating between 70 to 80 °C.
  • Sterilization technique can destroy both vegetative cells and spores of many microorganisms due to its high temperature treatment, but pasteurization is used to suppress microbial growth and it can destroy only the vegetative cells of many microorganisms and not their spores.
  •  The properties of food can be highly changed with the sterilization process unlike with the pasteurization process.
  • Due to the low temperatures, pasteurization can be applied for highly heat sensitive foods with high nutrient levels. Sterilization can only be applied for certain foods, which are not very heat resistant.
  • Unlike in the process of pasteurization, nutrients of food can be easily destroyed in the process of sterilization even though it extends the shelf life of foods.