Optimization Of Technological Parameters And Physical-Chemical Properties Of Milk By Ultra-High Pressure Water Jet Technique

At recent market there are two kinds of liquid milk:pasteurization of milk and ultra-high temperature (UHT) milk. Because of the lower temperature, pasteurization milk lose less nutrient, but shorter shelf life;instantaneous UHT milk has higher temperature in sterilization treatment, so has long shelf life, but lose more nutrients.Both exist the issues:high energy consumption, nutritional composition and shelf life can not take into account.This topic use high pressure water jet method (UHP) to precess milk based on the sterilization theories of injured cell wall, damaged cellular membrane, protein denaturation,and the effect of hyperpressure, high-velocity impact and thermal coordination,and by the means of collision and opposed collision.By measuring the sterilization rate,the data of some physical and chemical indicators and lipase activity, it can get the following results:①To precess milk at 50MPa (4℃injection), they can meet the standard of pasteurized milk:total numbers of colony count≤30000cuf/ml;at 100MPa,they can fit for the standard of pasteurized milk:coliform colony≤90MPN/100ml;②the milk processing at 50MPa is overtopping than pasteurization of milk's shelf-life(3 to 5 days), at 200-300MPa the shelf-life is up to 65 days or longer (135 days), more than the UHT(composite film)'s (1 month), clarifying the high pressure jet can extend effectually the shelf life of milk;③The maximum precessing temperature is 80℃, far lower than the temperature (135～150℃) by UHT processing and the processing time is shorter than the pasteurized milk(10s～20s), and the protein denaturation is smaller than UHT milk, indicating that high pressure jet technology is more conducive to preserve the nutritional quality of milk.;④Between 50MPa～250MPa, with the increasing pressure, the mean diameter of milk significantly reduced, shows the good effect on homogening; above 300MPa the mean diameter increased more than origin milk, indicating occurrence of milk gelation changes;⑤The best technique:in 2～6℃, at 100MPa to precess milk by opposed collision, can accord with< Pasteurization, sterilization milk hygiene standards >(GB 19645-2005).These results sufficiently show that high pressure water jet is an environmental protection, high efficiency, no pollution method and can be used in milk sterilization. The high pressure jet is feasible in fresh milk procession as a cold sterilization.With the wide application of this technology,it is expected to form a new type of liquid milk-high pressure milk.