Question

(a) Describe the differences between dry heat, moist heat, and pasteurization. Give an example of each. (b) A population consists of 10,000 bacterial cells. It is treated with a sterilizing agent. The environment with this population becomes sterile in two hours. What is its D-value?

Answer 1

Answer:

Dry Heat

It is the process in which bacterial spores and microorganisms are killed by using a high temperature (160 - 180 Celcius) which causes the destruction of vital cell components such as proteins (i.e, enzymes) and nucleic acids by denaturation due to oxidation.

Example: Examples of dry heat are instruments which give hot air in a contained environment such as hot air oven, microwave oven. Also processes like incinerating, flaming, radiation are also dry heat sterilization methods.

Moist Heat

It is the process in which bacterial spores and micro-organisms are killed by using high-pressure steam, in latent heat which is more effective than dry heat as moist heat causes coagulation and denaturation of the proteins (i.e, enzymes) of the micro-organisms at a much lower temperature as compared to dry heat and at a faster rate by using liquid (i.e, moisture). It can be used at a temperature of around 121 Celcius. It is above the boiling point.

Example: Moist heat can be used when a pressurized chamber like an autoclave is used.

Pasteurization

It is the process which is mainly used to kill micro-organisms which can cause spoilage of liquid food products such as milk and wine. It operates at a temperature lower than the boiling point. Thus, it doesn't kill all micro-organisms and only kills and reduces the viability of micro-organisms to reduce spoilage of food. It operates at a temperature of around 63 Celcius.

Example: Pasteurization is often used when milk is overheated by high-pressure processing (HPP or pascalization) or by electrical fields (PEF) pasteurization.