Sterilization of milk

Milk as it exists in the udder of the healthy cow is devoid of bacteria, as is also that of the human subject; germs of an offending nature reach the milk after it has left then animal.

The fact is well-known that milk under goes a number of chemical changes in its constituents some hours after milking. It becomes sour, owing to the decomposition of the milk sugar, the case in separates, and finally putrefactive decomposition begins.

These changes are induced by the presence in milk of bacteria, which for the most part do not generate diseases, but which maybe, and often are, accompanied by bacteria capable of causing disease that obtain access to the milk from the body of the animal, from the air, from the water that was used to wash the cans, from the hands, clothing, and person of the milker, and the like.

Sterilization of milk is made to obtain a safe product from sanitary-and-hygienic point of view and to provide its long storage at an ambient temperature without the change in quality. Sterilization is the killing or removal of all microorganisms, including bacterial spores which are highly resistant. Sterilization is an absolute term, i.e. the article must be sterile meaning the absence of all microorganisms.

It is the process of heating to a high enough temperature (usually more than 100°C) for specific time to kill almost all bacteria. The sterilized milk can be stored at room temperature for a long period of time. The sterilization of milk has the following characteristics.
•Temperature more than 100°C is used in the process.
•No chilling is required for storage. Excellent storage life at room temperature.
•High operating pressure is employed to prevent milk from boiling at the processing temperature.

Long storage life and the possibility of storage at usual temperature modes allow transporting this production to distant regions. Consumers are attracted by the guaranteed product quality and the possibility to use it while traveling.
Milk Processing: Sterilization of milk

Dry heat sterilization

Heat is used as the sterilant for aseptic systems as a natural extension of thermal processing. Dry heat is used for the sterilization of glassware, metal instruments, certain plastics and heat-stable compounds.

Dry heat sterilization as the name indicates, utilizes hot air that is either free from water vapour, or has very little of it, and where this moisture plays a minimal or no role in the process of sterilization.

This sterilization method is often used for heat-stable oils, ointments and powders. Most often, depyrogenation of parental containers is performed utilizing a dry heat oven. Dry heat is considered to be the most reliable method of sterilization of surfaces and utensils that can withstand heat. For dry heat sterilization to be archived a constant supply of electricity is necessary.

Dry heat is believed to cause oxidation rather than denaturation of proteins, although the effect of the presence of oxygen is not significant. Dry heat requires higher temperatures for longer duration than moist heat for sterilization because heat conduction by the former is lower than the later.

In the heat sterilization of foods, control of side reactions is very important in practice. Many reactions, such as destruction of vitamins, oxidation of lipids, and browning, take place during heat treatments.
Dry heat sterilization

Irradiation sterilization

Irradiation or ionizing radiation is a type of ‘cold’ sterilization, where the piece being sterilized is not exposed to heat. However, due to the poor heat transfer properties of many types of products, small increases in temperature above ambient can occur in the irradiated product.

Similar to sterilization by heat that requires high temperatures for specified times, sterilization of foods by irradiation requires high enough radiation doses to inactivate bacterial spores.

Radiation sterilization can be accomplished using one of three forms of radiation: gamma sterilization using radioisotopes, electron beam using electron accelerators, or beta radiation using an electron accelerator.

The irradiation sterilization process extends beyond treatment of health care products to commodities and irradiation of food to destroy pathogens such as salmonella and E. coli to make our food safer to eat.

Irradiation sterilization of foods, including meats and poultry, was extensively studied in the 1950s and 1960s, mostly by the US government. Irradiation sterilization effectively kills microorganisms because of its ability to break the chemical bonds of organic compounds, producing highly reactively species known as free radicals.
Irradiation sterilization

Sterilize in place (SIP)

Sterilization-in-place (SIP) refers to the practice of sterilizing process equipment or materials in process at their place of use or installed location. It has been developed from the requirement to sterilize equipment that is too bulky or heavy to be moved into autoclaves or ovens.

SIP is a very important technology, needed for microbiological control during production. When the term is used, it is always referring to steam sterilization of large equipment items such as mixing tanks, vessel-filter-filler systems, and even complete isolator units.

The sterilization of these vessels and chambers is accomplished using direct contact with steam in an overkill process that is adapted from that used in steam autoclaves for individual smaller items.
Sterilize in place (SIP)

Food sterilisation

Sterilisation is a technique to prolong the shelf life of foods.  It is the complete destruction or elimination of all viable organisms in/on a food product being sterilised.

For some canned products they are heated for up to one hour. All micro-organisms are killed during this process. After sterilisation the product is free of germs and, if stored correctly, have a shelf life of several years.

Classical sterilisation treatments are subdivided into two categories: sterilisation by heating (thermal processing) and sterilisation without heating (non-thermal processing).

Thermal processing is widely practiced in spite of some problem such as that the process might reduce nutrition or deterioration the quality of foods.

Non-thermal processes include high pressure processing, pulsed electric fields, ultraviolet radiation, food radiation, chemical treatments, and use of magnetic fields.

Thermal processing is further divided into two categories as in-container sterilisation and aseptic sterilisation.
Food sterilisation