Changes In Peptides During The Fermentation Of Cream Cheese And Their Effects On The Formation Of Volatile Compounds

Fermented thin cream cheese is a dairy product made from thin cream as raw material,which is fermented after acid coagulation and protein precipitation.The types of microorganisms involved in the fermentation process and different process conditions will have a significant impact on the quality of its product.Peptides are metabolites of protein degradation,which not only affect the nutritional value of food,but also produce volatile flavor compounds through microbial metabolism.Therefore,exploring the dynamic changes of peptide substances and their impact on flavor compounds is crucial for improving the quality and controlling the quality of cream cheese.This project first determined the optimal fermentation process for cream cheese,and took the optimal fermentation time before and after as the research object to explore the quality changes,protein degradation,microbial succession,and metabolic changes of cream cheese at different fermentation stages.Through correlation analysis,the influence of peptides on flavor formation was explored.The research results of this topic provide a theoretical basis for the impact of peptides on flavor,and also provide a scientific reference for improving the quality of cream cheese.The specific research is as follows:(1)Research on optimization of cream cheese process and protein degradation:using sensory evaluation as the indicator,single factor and response surface optimization experiments were used to optimize the fermentation process of cream cheese,and the optimal fermentation process was determined:fermentation time of 10 d,fermentation temperature of 16℃,and citric acid addition of 4.5%.Under these fermentation conditions,cream cheese has a soft and silky taste,with a high sensory score.In addition,the trend of texture changes during the fermentation process is different,with significant changes in pH and water content(P<0.05).Protein and fat content have decreased,and protein degradation occurs.(2)Changes in flavor substances during the fermentation process of thin cream cheese:a combination of HS-SPME-GC-MS and HS-GC-IMS methods was used to detect flavor substances in thin cream cheese at different fermentation time periods(0,5,10,15,and 20 d),and key flavor substances such as 2-heptanone,acetoin,2-undecanone,2,3-butanediol,etc.were screened using OAV and stoichiometry.It was also found that HS-GC-IMS and HS-SPME-GC-MS have different detection capabilities for flavor substances.The detection method of HS-SPME-GC-MS is more sensitive to acids,but HS-GC-IMS is more accurate in detecting esters.(3)Succession of microbial community structure during the fermentation process of cream cheese:16SrRNA sequencing technology is used to analyze the diversity of microbial community structure and composition during the fermentation process of cream cheese.The results showed that the microbial richness of cream cheese was the highest on the 0th day of fermentation,and it was inhibited after the 10th day of fermentation,with most of the microbial richness decreasing or even disappearing.At the end of fermentation(20 d),the number of microorganisms slightly rebounded.The key microbial genera are Pseudomonas,Xanthomonas,Leuconostoc,Acinetobacter,Pediococcus,Lactobacillus,Lactococcus and Methylbacillus.Key microbial phyla include Proteobacteria,Fusobacteria,Firmicutes,and Cyanobacteria;Redundancy analysis shows that pH and total acid are the two environmental factors that have the greatest impact on microorganisms.(4)Research on the effect of peptide metabolism on flavor formation:The metabolic changes of peptide compounds during the fermentation process of cream cheese were studied using LC-MS/MS technology.The results showed that there was a total of 23 differential metabolites related to protein degradation,including 4 peptides,namely Leu-Leu,Phe-Ile,Leu-Pro,and Ile-Val.Through the correlation analysis of peptides and microorganisms,the results showed that Fusobacteria,Bacillota and Leuconostoc were significantly positively correlated with Leu-Leu,Phe-Ile and Leu-Pro.According to the metabolic pathway analysis,Phe-Ile can be degraded to produce Phe and Ile under the action of Bacillota,Leuconostoc and other microorganisms.Phe is further metabolized to produce phenethyl alcohol and phenylacetaldehyde.Leu-Leu and Leu-Pro can also be degraded by Fusobacteria,Bacillota and Leuconostoc to produce Leu.Leu further metabolizes to produce 3-methylbutanal and 3-methylbutanol.