Optimization Of Technological Parameters And Physical-Chemical Properties Of Sterilized Milk By Ultra-High Pressure

The milk is rich in nutrition food .It contains a great variety of nutrition ingredients and immunological factors. In order to keep shelf life, the natural milk must be sterilized. The traditional heating-sterilization means will break down the nutrition components and flavor materials .While ultra high pressure (UHP) sterilization technology was a non-heating technology, It not only can achieve the same effects of heating sterilization, but also can hold the nutrition components and flavor materials.UHP technology was used to sterilize in fresh milk. Technology parameters were optimized. Sense characters, Physical-Chemical characters and microscopic structure of ultra high pressure sterilized milk were researched. Valuing the nutrition, stability and safety, ultra high pressure sterilized milk was compared with the raw milk, pasteurized milk and ultra high temperature milk.The main results were as follows:1. The colony count and coliform bacteria was used to value factor.The sterilization regularity of treatment pressure and time was gained. The optimum conditions of UHP sterilization milk were obtained by orthogonal experiment. The results indicated which low pressure was 150MPa, low pressure treatment time was 5min, high pressure was 500MPa and high pressure treatment time was 40 min. The results of thermal insulation test show colony count and coliform bacteria have satisfied the requirement of food business.2.After UHP sterilization,the brightness and turbidity of UHP milk were reduced and the sense properties was changed,but the content of dissociate calcium increased and the denaturalization degree of whey protein was reduced,thus the nutrition value of milk was preserved furthestly. While pasteurized and ultra high temperature (UHT) sterilization can increase the brightness and turbidity of milk, and also changed the sense properties, but the content of dissociate calcium was reduced and the denaturalization degree of whey protein increased, which reduced the nutrition value of milk.3. After UHP treatment, the all free amino acid can be measured except alanine and cystine and the lower content of asparagines. Appropriate heat treatment can increase the content of free amino acid, but a part of free amino acid will be destroyed or lossed with the heat temperature gradually increased. A comparison among UHP milk, pasteurism milk and UHT milk showed the content of free amino acid is the highest in UHP milk, the pasteurism milk is second, the UHT milk is lowest.4. Casein micelles are ripped after treatment of UHP and the diameter diminished, Fat ball dimeter augmented appreciably. The diameter of Casein micelles and fat ball in pasteurism milk is augmented appreciably. The Casein micelles structure of UHT milk is loosen and the diameter is augmented distinctly, as well as homogenization treatment dimished the fat ball diameter.