Effect Of Transglutaminase On Curd Characteristics And Flavor Quality Of Fermented Goat Milk

Fermented goat milk has outstanding nutritional value,but its curd characteristics are poor during processing and whey is easy to separate out,which leads to difficulties in processing.This kind of problem can be improved by adding transglutaminase(TGase).Therefore,this experiment took stirred fermented goat milk as the research object,and added TGase before fermentation to study the effects of TGase on the physicochemical properties,curd,texture,microstructure and flavor quality of fermented goat milk during preparation and storage,so as to provide theoretical basis for quality control of fermented goat milk.The research contents were as follows:(1)Optimization of fermented goat milk treated with TGase.Single factor and orthogonal tests were conducted on TGase treatment method,treatment temperature,addition amount and treatment time with viscosity as the detection index.The appropriate scheme was determined as adding TGase after sterilization of the restored milk,treatment temperature of 40℃,addition amount of 0.8 g/L,and treatment time of 1.5h.The viscosity of fermented goat milk under these conditions reached 1934±24.25 m Pa.s.(2)Effect of TGase on curd quality during the preparation of fermented goat milk.Taking untreated goat milk as control,the physicochemical,curd,texture and microstructure characteristics of fermented goat milk treated with TGase during fermentation and post-maturation were investigated.It was found that TGase could shorten the curd time of fermented goat milk and weaken the post-acidification degree of fermented goat milk.At the same time,TGase treatment can significantly enhance the viscosity,water retention,texture properties and protein crosslinking degree of fermented goat milk,so that the microstructure is closer,and the curd quality is improved comprehensively.(3)Effect of TGase on flavor quality of fermented goat milk.GC-IMS was used to explore the composition and differences of volatile compounds in fermented goat milk during fermentation and after-ripening.A total of 42 flavor compounds were detected.Fermentation reduced the smell of goat milk,such as heptaldehyde and hexanal,and effectively reduced the smell of goat.Moreover,after fermentation,10 kinds of goat milk flavor compounds were increased,which made the goat milk flavor more intense.(4)Study on quality characteristics of fermented goat milk.The effects of TGase treatment on the physical and chemical properties,viable count,sensory quality and metabolites of fermented goat milk were investigated.It was found that compared with the blank group,TGase treatment reduced acidification degree,enhanced sensory quality and produced differences in metabolite composition,including 99 up-regulated metabolites and127 down-regulated metabolites.The key up-regulated metabolites were glycerophosphoric acid,5 ’-thymidine acid and L-tyrosine,which were presumed to be related to nucleotide metabolism,valine,leucine and isoleucine synthesis.(5)Effect of TGase on storage quality of fermented goat milk.The physical and chemical characteristics,the number of lactic acid bacteria,tissue state and flavor quality of fermented goat milk during storage for 28 d were analyzed.It was found that TGase could significantly weaken the post-acidification of fermented goat milk and had no obvious effect on the number of viable bacteria.Both groups of fermented goat milk reached the highest value of texture and flavor on the 7th day of storage,and then the quality of the blank group began to deteriorate.TGase treatment could keep the fermented goat milk in a stable state of high viscosity,low whey precipitation,high texture characteristics and high flavor for a long time.