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

Process of canning effects on vegetables

From the textural standpoint, vegetables may be divided into those that are eaten raw and valued primarily for their crispness, those that are eaten cooked and valued for their softness and those that can be consumed in either form such as cauliflower and carrots.

Vegetables like peas, beans, greens are sometimes canned. The retention of original color is of great importance effecting the marketability and consumer response.

In the process of canning, vegetables are heated to destroy spoilage disease causing microorganisms.

Such heat treatments also produce a number of of undesirable chemical and textural changes in the vegetables. The textural changes are due to partial destruction of the cell wall and cell membrane.

Blanching, plus the strong heat treatments applied to nonacid vegetables, appears to be responsible for the large vitamin losses in canning.

Heat treatments also cause chemical alteration of the green pigment chlorophyll, thus resulting in a processed vegetable with less green color.

During canning chlorophyll gets converted to pheophytin due to the high temperature used. Sometimes to retain the color and to neutralize the acid, alkali is added.
Process of canning effects on vegetables

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