Study On Screening Of NSLAB In Goat Cheese And The Role Of NSLAB Accelerating Cheese Ripening

Due to consumers'special flavor and nutritional and probiotic preference for goat cheese,the research on goat cheese has shown an increasing trend in recent years.Goat cheese has become an indispensable food in its diet.However,due to the limitation of production and the rare milk source,the manual production mode of goat cheese and the difference of processing techniques,the risk of goat cheese is uneven,the quality of goat cheese is low and it is easy to go metamorphism and the pathogenic microorganisms breeds.In order to provide consumers with high quality cheese that is safe,consistent in taste and relatively short in maturity,producers and researchers are beginning to explore the use of non-starter lactobacillus?NSLAB?.Adding the right NSLAB can speed up the cheese repining and improve the flavor of the cheese.In order to obtain NSLAB with excellent production performance for accelerating the maturity of high quality goat cheese,this study analyzed the microbial flora in several handmade goat cheeses in the Mediterranean region,and obtained NSLAB by using the traditional isolation and culture methods.Through the screening of fermentation characteristics of NSLAB,NSLAB with excellent production performance was obtained,and the strain was further applied to the processing of goat cheese.The mechanism of NSLAB-accelerated cheese ripening was comprehensively analyzed.Therefore,this study provides a theoretical basis for the production of high quality and fast mature cheese.Microbial analysis of eight handmade semi-hard goat cheese samples from the Mediterranean region was carried out by Illumina Miseq high-throughput sequencing.The results showed that the microbes in the samples exhibited different diversity;however,all samples had the same dominant bacteria?Firmicutes?.At the genus classification level,Lactobacillus occupies the highest proportion,followed by Lactococcus,Enterococcus,and Leuconostoc.Because NSLAB is a secondary flora,in addition to Lactobacillus,Enterococcus and Leuconostocs are distributed in individual samples,but the relative abundance is not high.66 strains of NSLAB were isolated from goat cheese samples,and their optimum growth temperature,salt tolerance,exopolysaccharides?EPS?,and diacetyl production capacity,acidification ability,autolysis,and protein and fat hydrolysis ability were compared.Among them,25 strains of NSLAB exhibited strong growth ability at 37°C,and 16S rDNA sequence analysis showed that they belonged to Lactobacillus,including 16 strains of Lb.paracasei and 9 strains of Lb.rhamnosus.Among the 25 strains of NSLAB with strong growth ability,8 strains show strong salt tolerance,weak acidification ability,high autolysis ability,EPS and diacetyl ability,and strong proteolytic activity.To further compare the proteins degradation ability of LAB,synthetic substrates were used to investigate the peptidase hydrolysis system of NSLAB.The results showed that 8 strains with excellent production performance secreted the same type of peptidase;nonetheless,significant differences were observed in peptidase activity.Determination of aminopeptidase activity using Lys-?NA,Leu-?NA and Pro-?NA as substrates,Determination of dipeptide aminopeptidase activity by Gly-Pro-?NA and Arg-Pro-?NA,Endopeptidase activity was determined using NBZ-Tyr-?NA as a substrate,Detection of dipeptidase activity using Leu-Leu,Lys-Leu and Ala-Phe as substrates,Strains A-3,D-3 and D-8 showed higher enzyme activities.Comprehensive consideration of pH conditions,NaCl concentration,CaCl₂concentration,temperature and metal ions affect the aminopeptidase activity of NSLAB strain,and pH,NaCl concentration and temperature affect the autolysis of NSLAB strain,this study screened the excellent NSLAB strains A-3 and D-3 which can achieve the highest performance in the cheese ripening process.Comprehensive consideration of pH 4.6-SN/TN,12%TCA-SN/TN,5%PTASN/TN,SDS-PAGE electrophoresis,RP-HPLC and free amino acid analysis showed that the addition of NSLAB increased the peptidase and promoted the protein of cheese.Hydrolysis significantly increases the free amino acid content.From the sensory evaluation,it can be concluded that the added NSLAB strain significantly improved the astringency of the cheese in the late stage of cheese ripening,significantly enhanced the strength and persistence of the enhanced cheese flavor,and did not bring bitterness,spoilage,feed taste,sourness.The production of the defective flavor;texture analysis showed that the addition of A-3 did not significantly change the hardness of the cheese,but also increased the elasticity of the cheese.By analyzing the influence of NSLAB strain on cheese composition,protein hydrolysis,texture and flavor,it was found that the production performance of NSLAB strain has an important effect on the maturation of cheese.A-3 and D-3 can promote protein degradation,promote the ripening of the cheese and the improvement of the cheese texture enhance the strength and persistence of the cheese flavor and have potential for practical application.