Thermal Sterilization Of Canned Liquid Foods

Sterilization of food involves the destruction of microorganisms carried in it so that the food can be stored longer and be safe to consume. Thermal sterilization is the most often used and most time-tested method of sterilization. It involves use of heat to destroy the harmful microorganisms. But heat also affects nutrients and other desirable food properties adversely. Design of sterilization processes involves selection and implementation of heating temperature and duration to minimize the destruction of desirable food components while maintaining the required level of destruction of the harmful microorganisms (1,2).

Due to the finite size of any food material, time-temperature histories will always vary spatially, the exact variation being a function of the food properties, the design of the machinery, and the properties of container (batch) or tube (continuous). Only by analyzing all of these factors, which requires detailed heat transfer studies, would the required time-temperature history be known. Sterilization of liquids is further complicated because it is not the time-temperature history of locations but that of the individual moving liquid particles that determine the extent of sterilization, the latter being difficult to observe experimentally or to calculate theoretically.

The sterilization literature spans more than 100 years. Most studies are product, process, or equipment specific. The studies generally do not explain the underlying physics in sufficient detail to be able to make generalized conclusions about a large category of problems. This article synthesizes the engineering studies of liquid food sterilization to provide insight into the underlying physics of the process. After introducing the general concepts involving heating of fluids, three broad categories of liquid food sterilization systems are discussed in detail. These are continuous heating, agitated containerized heating, and unagi-tated containerized heating. Included under each category are a brief description of the processing equipment, methods of heating, flow and temperature profiles, sterilization values, effect of non-Newtonian liquid behavior, and effect of presence of particulates.

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