Effect Of Different Storage Temperature On The Quality And Microorganism Of Pasteurized Milk

Pasteurized milk is favored by consumers because it retains the main nutrients and flavors of fresh milk.However,due to the low temperature of sterilization,it cannot kill all the microorganisms and enzymes in fresh milk,there are still some heat-resistant bacteria and Heat-resistant enzymes will remain in the product.The product’s shelf life is very short.A slight carelessness can lead to spoilage.In the subsequent storage,transportation,sales and consumption,it must always be kept in the cold chain.However,at present,it is difficult for many places in China to maintain such stringent storage,transportation,and marketing conditions.This,coupled with excessive dependence on raw milk,has caused pasteurized milk to still not be able to be produced in large-scale production and remotely circulate in different places in China.Sales have greatly hampered the processing and widespread consumption of pasteurized milk.In this study,pasteurized milk produced on the same day as the normal process of domestic large-scale dairy companies was stored at different temperatures and times for sampling.Sensory scores,electronic tongues,and color difference meters were used to sense the pasteurized milk samples under different storage conditions.Quality analysis,by analyzing the acidity,pH value,alcohol positive milk,density,conductivity,etc.Its physicochemical properties were analyzed by determining its protein,fat,non-fat milk solid(SNF)of its nutritional composition Analysis,and then using amino acid automatic analyzer and Fourier near infrared spectroscopy to analyze the free amino acid and protein secondary structure.Finally,the exact species of the heat-tolerant microorganisms in pasteurized milk samples with different storage conditions were analyzed by combining metagenomic techniques.The results showed that the exact types of thermophilic microorganisms that were retained and their effect on product quality were as follows:1.Pasteurized milk shares Mycoplasma,Oxalobacteraceae,Pseudomonas,Actinetobacter,Streptococcus,etc.after packaging.Bacterial genus;2.The key points of significant changes in nutrient composition,physicochemical properties,and microbial diversity were storage within 12 days of storage at 0°C,storage at4°C for 9 days,storage at 10°C for 6 days,storage at 15°C,25°C,and 37°C.Therefore,it is recommended to store at 0°C for 12 days,store at 4°C for 9 days,and store at 10°C for 6 days.Storage at 15°C,25°C,and 37°C is not recommended.3.The results of diversity index analysis show that The microbial diversity of pasteurizedmilk stored at 0°C remained the most complete,and its nutritional quality was also maintained at 0°C;and it was pasteurized at 4°C,10°C,15°C,and 25°C.Microbial diversity and nutritional quality have a greater impact,and the higher the storage temperature,the greater the impact.Comprehensive data analysis revealed that the previously undetected genus Bacillus appeared at the critical time points of 9-day storage at 4°C,6-day storage at10°C,and 3-day storage at 15°C and 25°C.Paenibacillus,a genus of Serratia,presumably speculates that these two species of bacteria are the key determinants of the spoilage of pasteurized milk.However,the response caused by these two species needs further study.