Retort Pouch


Thermal sterilization is one of the most effective means of preserving a large part of our food supply. The objective of sterilization is to extend the shelf life of food products and make the food safe for human consumption by destroying harmful microorganisms.

A sterilizer is a unit in which food is heated at high temperature and then held at that temperature for a period sufficient to kill the mircroorganisms of concern from the foodproduct.

A sterile product is one in which no viable microoganisms are present. A viable organism is one that is able to reproduce when exposed to conditions that are optimum for its growth. Temperature slightly higher than the maximum for bacterial growth results in the death of vegetative bacterial cells, whereas bacterial spores can survive at much higher temperatures.

Since bacterial spores are far more heat resistant than vegetative cells, they are primary concern in most sterilization processes. Saturated steam is the nost commonly used and highly desirable heating medium for commercial sterilization of canned food.

In the thermal processing, which represents the most common technique used in food preservation today, the study of heat penetration into foods is of great importantce. The factors that influence the rate of heat penetration are as follows:

1) Product Specification. Liquid or particulate foods in which natural convection is established heat faster than solid foods in which heat is transferred by conduction. The low thermal conductivity of foods is a major limitation to conduction heat transfer.

2) Size of the container. Heat penetration to the center is faster in small containers than in large container

3) Temperature of the retort. A higher termperature difference between the heating medium and food causes faster heat penetration.

4) Shape of the container. Tall containers promote free convection currents in convective heating of foods and hence faster heat penetration.

5) Type of container. Heat penetration is faster through metal walls than glass or plastic walls of the container because of the higher thermal conductivity of the metal than that of glass and plastic.

The time needed to destroy 90% of the mircroorganisms (to reduce their numbers by a factory of 10) is defined as decimal reduction time (Dt). It is the time required for a one-log cycle reduction in microbial population. Dt values differ for different microbial species. The larger Dt value at a given temperature indicate higher thermal resistance of the microbial population.


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