| Goat milk has a unique flavor and rich nutrition,but it has also become a natural medium for microorganisms,and is easily contaminated by various pathogenic microorganisms and spoilage microorganisms,leading to spoilage and deterioration,including pathogenic bacteria.Pathogenic bacteria not only seriously affect the quality of raw milk,but also pose a huge threat to the safety and health of consumers.Ultrasonic sterilization technology can reduce or inactivate microorganisms and has no negative impact on product quality.It is a promising alternative to traditional thermal sterilization technology.Therefore,this paper studied the bactericidal effect of ultrasonic treatment on Escherichia coli and Staphylococcus aureus in fresh goat milk,as well as the influence of ultrasonic sterilization technology on the microbial diversity and physicochemical quality of fresh goat milk,so as to provide reference for the non-thermal sterilization and product development of goat milk.The main research contents and results are as follows:1.During ultrasonic treatment of fresh goat's milk,ultrasonic power,ultrasonic temperature and ultrasonic time significantly affected the inactivation effect of ultrasonic in goat's milk on E.coli and S.aureus.With the improvement of ultrasonic power,ultrasonic temperature and ultrasonic time,the bactericidal effect on Escherichia coli and Staphylococcus aureus was continuously enhanced.At the factor level studied,the influence degree of three factors on the inactivation efficiency of the two bacteria was successively ultrasonic temperature>ultrasonic time>ultrasonic power.The objective of the sterilization pair value of pathogenic bacteria recommended by the FDA of the United States was?5 logCFU/mL.The optimal sterilization conditions of the two bacteria in goat's milk obtained by response surface experiment were ultrasonic power 500W,ultrasonic temperature 60? and ultrasonic time 10min.2.Ultrasonic treatment severely damages the bacterial structure of E.coli and S.aureus.Therefore,the sterilization mechanism of ultrasonic may be caused by the significant damage to the ultrastructure of the cell,causing its content to flow and die.Compared with balsam milk,ultrasonic milk had better bactericidal effect.After 21 days of storage at 4?,the total bacterial colony of ultrasonic milk was 2.71ogCFU/mL.E.coli and S.aureus were not detected during the storage period,which still met the national standard.Compared with ultrasonic milk,at 21 d,the solids,milk fat and milk protein of non-fat milk were lower than that of ultrasonic goat milk.Lactose and inorganic salt had lower content,so the difference was not significant,and the density and acidity were significantly higher than that of ultrasonic group.The effect of the two sterilization treatments on SDS-PAGE of goat milk protein was not significant,and there was no significant difference between the protein content of ultrasonic milk,pasteurized milk and raw milk(P>0.05).The result is that at 4? storage,goat milk after pasteurization can be preserved for about 14 days,while milk after ultrasonic sterilization can be preserved for about 21 days.3.At phylum level,the main dominant bacteria in the three groups of samples are all Proteobacteria,and the content of Proteobacteria in the ultrasonic sterilization group is lower than that in the raw milk group and pasteurization group.At family level,the dominant flora of each group of samples was different.At genus level,the dominant bacteria in raw milk are Acinetobacter,Klebsiella,unclassified and Raoultella(in order of abundance).The dominant bacteria in ultrasonic sterilized milk are unclassified and Acinetobacter.In pasteurized milk,unclassified has always been its dominant genus.Proteobacteria may be the main reason that causes goat milk microorganisms to exceed the standard.Moraxellaceae and Enterobacteriaceae belong to the Proteobacteria.Acinetobacter,Klebsiella,Raoultella may be a key bacterium that causes spoilage of goat milk. |
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