ABSTRACT
The classical approach to overcome or at least minimize these undesirable quality changes in thermal processing is the HTST (high temperature short time) concept. HTST is based on the fact that the inactivation of microorgan isms is primarily dependent on the time of the heat treatment, whereas quality changes are primarily dependent on the time duration of the heat treatment (Ohlsson, 1980). High temperatures will give rapid inactivation of microorgan isms and enzymes, which are goals of pasteurization or sterilization, and short times will give fewer undesired quality changes. The problem in applying this principle to solid and high-viscosity foods is that the parts of the food in contact with the hot surfaces will be overheated during the time needed for the heat to transfer to the interior or coldest part of the food. The surface overheating will give quality losses in severe cases due to the low heat diffusivity of foods. Thus, direct volume heating methods are seen as minimal processing methods, where the thermal processing is applied to minimize the quality changes of the process (Ohlsson, 1994).
