Pasteurization is the process of heating foods to the extent that the heat inactivates a substantial number of the pathogens in the food so that the remaining ones do not disease, but not to the extent that the heat alters the taste and quality of the food significantly. It is akin to partial sterilization. Full sterilization kills all micro-organisms but also alters the chemistry of the food.
Pasteurization is commonly associated with milk but also widely applied to fruits as part of processing them for jams, jellies, syrups, juice and canning. Very often, it is the semi-processed pulp of the fruit, purees or juice extracts obtained by pressure or other means rather than the whole fruit that is subject to pasteurization.
Bacteria, molds and spores face destruction when exposed to a certain minimum temperature for a certain minimum time. Ultra-pasteurization, which is akin to the sterilization of fruits and fruit juices, may alter the taste of the fruit, and moreover, cause deterioration of the pectin substances inherent to fruits. As such, the best option to pasteurize fruit is a moderate course that keeps the food in-between its raw state and ultra-pasteurized state.
Food pasteurizing time and temperature depends on the pH of the food. Fruits have a low pH that is usually below 4.5. This means that pasteurization inactivates harmful enzymes such as pectinesterase and polygalacturonase by applying the required temperature for a relatively short time.
In contrast, milk, which has a higher pH, requires more severe heat treatment to inactive the pathogenic bacteria and requires refrigeration post pasteurization to ensure that the remaining bacteria do not multiply and grow to unacceptable levels.
One best practice is to de-aerate the fruit before pasteurization to remove oxygen and reduce the oxidative degeneration of the food.