Analysis And Research On The Quality Of Probiotics Dairy Products In Shelf Life

Probiotics can improve the balance of microbial flora in the body and have a positive effect on the health of the body.Natural milk is the best carrier for probiotics.Probiotics dairy products that are processed through the organic combination of probiotics and milk are increasingly preferred by researchers and the business community and consumers because they are rich in nutrition with a variety of effects.At present,probiotic dairy products is developing rapidly,with a wide range of species,and the types and quantities of probiotics added to them are increasing.However,there are still some limitations in the evaluation of their quality.Therefore,high and low qualities of products and the limitations of monitoring will continue to appear,resulting in a certain degree of difficulty in the supervision of their products.This study intends to systematically investigate and test the probiotic dairy products sold in the market,as well as the storage and experimental studies,as well as the analysis and species identification of the types and quantities of probiotics,in order to improve the technical quality of probiotic product quality monitoring.Through the study,the following results were obtained.Study on quality analysis of sample shelf life:A total of 104 probiotic products were investigated in 10 large-scale dairy companies.The shelf life of fermented milk is generally 21 days,and probiotic milk drinks are generally 25or 30 days,indicating probiotic activity.There are 29 species of bacteria,accounting for 27.9%.The number of viable cells was generally 1.0×10~6CFU/mL or 1.0×10~8CFU/mL,and the product contained 87.5%of Streptococcus thermophilus and Bulgarian lactose.Statistics on the distribution of probiotics in the product showed that the proportions of Streptococcus thermophilus,Bulgarian lactobacillus,Lactobacillus acidophilus,Bifidobacterium lactis,Lactococcus lactis subsp.cremoris,Lactococcus lactis subsp.lactis,Lactobacillus paracasei,Lactobacillus plantarum,Lactobacillus longum,Lactobacillus casei,and Scorpion Scorpion were 90%,87.5%,36.5%,27.8%,15.3%,15.3%,10.5%,9.6%,8.6%,7.6%,3.8%,1.9%respectively;products containing one,two,three,four,five,six,or nine species of bacteria,accounts for 10.5%,44.1%,9.5%,20.1%,3.7%,6.6%,3.8%of the total surveyed products.Study on quality analysis of sample shelf life:The number of lactic acid bacteria,Lactobacilli,number of thermophilic streptococcus,and coliform bacteria in the shelf life of 26 kinds of dairy products with probiotics at the 4°C storage condition Changes in number,colony count,p H value,acidity,and sensory characteristics were analyzed and tested in15~30days.The results show that the coliforms were not detected;the total number of colonies is detected in 7samples,with the highest being 5.0×10~5 CFU/mL;The number of lactic acid bacteria in the initial period of shelf life is above 1.0×10~9CFU/mL,and it decreases to about 1.0×10~8CFU/mL after the shelf life.The amount of Lactobacillus and Streptococcus thermophilus over the entire shelf life was above 1.0×10~7 CFU/mL,but the number of cocci was significantly higher than that of bacilli;acidity,pH,and sensory changes were not significant during the shelf life.The overall quality level of the 26 products stored at 4°C complied with the relevant national standards.Sample temperature storage test:We selected 4 representative products and carried out storage experiments at 4°C,15°C,25°C and 37°C respectively.We analyzed and tested the same quality indicators as above.The results show that the shelf life is within 4°C.The tested indicators all met the relevant national standards.Although the number of lactic acid bacteria showed a downward trend,the number of viable cells on the third days after the 21 days of the shelf life was still above 1.0×10~8 CFU/mL;the acidity increased significantly at the 15°C shelf life,and the sensory quality decreased.On the 15th day,the number of viable lactic acid bacteria was above 1.0×10~7CFU/mL,and the coliforms were not detected;the acidity at the 5th day of shelf life at 25°C was greater than 120°T,and the number of lactic acid bacteria at the 7th day was 1.0×10~6CFU/mL,the coliform group was not detected,and the sensory quality declined rapidly.Overall,the quality index within 3 days to 4 days met the standard;the acidity at60th hour at 37°C had exceeded 120°T,and the sensory quality declined rapidly.The number of lactic acid bacteria was higher than 1.0×10~6CFU/mL at the 84th hour.Overall,the quality index within 2 days met the standard.Microstructure analysis of the sample:Analysis of the microscopic structure of the microbes in 12 samples and in the sample under the light microscope and electron microscope clearly showed the number of bacteria in the sample,and whether or not the sample contained cocci,bacilli,and double quinones.Bacillus can also roughly see the distribution of these three types of bacteria.Some bacilli may be isolated from specific species,but the length and shape of most bacilli strains may change with different treatment methods.Therefore,there are many same kinds of probiotics in the sample that require further identification to determine its species.Isolation and identification of probiotics in the sample:From the samples containing 9 probiotics,7 strains of lactic acid bacteria were isolated by the separation and purification of probiotics,namely LAB1,LAB2,LAB3,LAB4,LAB5,LAB6 and LAB7.Seven strains of Lactobacillus were identified from morphology and 16S rRNA.They were respectively Lactobacillus bulgaricus,Lactobacillus acidophilus,Lactobacillus casei,Lactobacillus rhamnosus,Lactobacillus plantarum,Lactobacillus longum,and Streptococcus thermophilus.The growth characteristics of the isolated seven strains of lactic acid bacteria were studied.LAB5 strains can grow at 15°C,and other strains cannot grow;only LAB7 strains can grow at 50°C,and the other 6 strains do not grow;the best growth temperatures of 7 strains were 37~45°C,30~37°C,37°C,30~37°C,37~45°C,37°C and 37~45°C respectively;the optimum pH were:5.5,6.5,6.0,5.5 6.5,6.5,and 6.5.The results of the growth characteristics were consistent with the identification results.At the same time,16SV3-V4MiseqPE300 was used to analyze the diversity of bacteria in this sample.The results of the identification were as follows:the sample contained Streptococcus thermophilus,Bifidobacterium animalis,Lactococcus lactis,Lactobacillus acidophilus and Lactobacillus bulgaricus.