Study On The Technology And Quality Of HTST Sterilized Milk With Long Shelf Life

Fresh milk is one of the important sources of human nutrients.In order to ensure the quality and safety of milk and extend the shelf life of products,heat treatment is usually used to kill microorganisms.While heat treatment ensures biological safety,it will cause a certai n degree of thermal damage,resulting in the reduction or loss of nutrients.Heat treatment of milk can induce physical and chemical reactions such as Maillard reaction,lactose isomerization,and protein denaturation,thereby affecting the flavor,nutrition,and functionality of milk.The milk on the Chinese market mainly includes pasteurized milk and ultra high temperature sterilized milk(UHT milk).Due to the incomplete market status of China's cold chain,normal temperature milk still occupies the main market of milk.In recent years,with the development of dai ry farming technology and the improvement of the breeding environment,the quality of raw milk in China has reached world-class levels,and the quality of raw milk produced by large-scale pastures has even exceeded that of developed countries such as Europe and the United States.However,the processing technology adopted by dairy processing enterprises is still UHT sterilization technology,which has great harm to heat treatment of cow milk,larg e loss of nutrients,and large changes in flavor.This article aims to explore the effect of different heat treatments on the physicochemical properties and flavor of cow's milk,combined with proteomics technology to further study the effects of different heat treatments on the glycosylation types and sites of milk protein,combined with a variety of physical and chemical indicators and comprehensive quality evaluation techniques for flavor changes,Propose a new thermal processing method to ensure the sh elf,while reducing the sterilization temperature to reduce the thermal damage of milk.Comparative analysis of 25 different heat treatment conditions of the cow's milk,the time setting were 5 s?10 s?15 s?20 s and 30 s,each heat treatment time corresponds to five heat treatment temperatures,75??90??105??120?and 135?,and compared with raw milk and pasteurized milk and UHT milk on the market.The results of physical and chemical analysis showed that the contents of the heat-sensitive indicators furfurine,lactulose,5-hydroxymethylfurfural and the degree of glycosylation of the protein increased sharply when the heat treatment temperature was higher than 120?or the heat treatment time was higher than15s.It can be seen that the Maillard reaction and the degree of lactose isomerization are intensified.And the study found that the main glycosylated proteins?-lactalbumin,?-lactoglobulin and k-casein.GC-MS flavor analysis results showed that the flavors of 120?/5s and 120?/15 s heat-treated milk were similar,and with the increase of heat treatment intensity,the types of flavor substances increased significantly.Among them,the relative content of aldehydes,ketones and esters increased significantly.The relative content of acids decreased significantly.In addition,the degree of heat treatment is different,and the difference between the odor and taste between the electronic nose and electronic tongue detection samples is significant.Combined with the above detection and analysis,when the heat treatment temperature is increased to above 130?,the flavor and nutritional value of the milk changes significantly.On the basis of the above-mentioned quality evaluation,a new thermal processing condition of120°C/15 s is proposed.This process can significantly reduce heat loss and improve flavor quality under the premise of ensuring shelf life.Using the pilot equipment,the raw milk was aseptically filled after heat treatment at 120°C/15s,and st ored at 4°C,25°C and 37°C for a45-day shelf life preservation experiment.Through the detection of changes in the milk's p H,protein particle size,Zeta potential,color,protease activity,and lipase activity during storage,the quality changes of the milk were comprehensively analyzed and compared with the UHT shelf life quality changes.Comprehensive analysis of the shelf life measurement indicators,the storage time of 120?/15 s heat-treated milk can be stored at 4 and 25?for up to 45 days,and at 37?for 30 days.The results of this study show that with the increase of heat treatment temperature and time,the milk quality changes in different degrees.When the temperature rises above 135?,the Maillard reaction of the milk increases,and the degree of thermal damage increases significantly.It is proposed that the new thermal processing method was 120?/15 s.When the total number of colonies of fresh milk before heat treatment is less than 5×10~4CFU/m L,the shelf life can reach more than 30 days.