Effects of Heat Treatment on the Nutritional Quality of MilkⅢ. Effect of Heat Treatment on Killing Pathogens in Milk

Abstract

A small amount of milk is sold as 'untreated' or raw in the US; the two most commonly used heat-treatments for milk sold in retail markets are pasteurization (LTLT, low-temperature long time; HTST, high-temperature short time) and sterilization (UHT, ultra-high temperature). These treatments extend the shelf life of milk. The main purpose of heat treatment is to reduce pathogenic and perishable microbial populations, inactivate enzymes, and minimize chemical reactions and physical changes. Milk UHT processing combined with aseptic packaging has been introduced to produce shelf-stable products with less chemical damage than sterile milk in containers. Two basic principles of UHT treatment distinguish this method from in-container sterilization. First, for the same germicidal effect, HTST treatments (as in UHT) use less chemicals than cold-long treatment (as in in-container sterilization). This is because Q10, the relative change in the reaction rate with a temperature change of 10°C, is lower than the chemical change during bacterial killing. Based on Q10 values of 3 and 10, the chemical change at 145°C for the same germicidal effect is only 2.7% at 115°C. The second principle is that the need to inactivate thermophilic bacterial spores (Bacillus cereus and Clostridium perfringens, etc.) determines the minimum time and temperature, while determining the maximum time and temperature at which undesirable chemical changes such as undesirable flavors, color changes, and vitamin breakdown should be minimized. Keywordsbacterial spore, thermoduric microorganism, Clostridium, low temperature long time(LTLT), ultra high temperature(UHT)