Studies Of Effect Of Starter Cultures On Proteolysis,Lipolysis And Flavor Formation Mechanism In Fermented Mutton Sausages

The typical quality and good flavor of fermented sausage are derived from the changes of physicochemical,biological and microbial processes in the fermentation and ripening process,during which the decomposition and oxidation of proteins and lipids play a decisive role in the final quality of sausage.Based on the goal of meeting the screening requirements of meat starter and the ability of production characteristics flavor substance,such as bacetoin,3-methylbutylaldehyde and hexanal,Lactobacillus sakei and Staphylococcus xylose with relatively high aroma production capacity were selected as starter cultures.The experiment was divided into compound starter cultures(LSS)group,a single wine lactobacillus(LS)group,controlled by natural fermentation(CO),which was designed to explore effect of starter cultures on proteolysis,lipolysis and flavor formation mechanism in fermented Mutton Sausages.The results were as follows.The starter cultures of Lactobacillus sakei and Staphylococcus xylose promoted the growth of Lactobacillus and Staphylococcus in sausage to 8.48-9.74 log CFU/g,as the dominant bacteria group.They promoted the rapid acidification of sausage,and the pH value(4.63)of the compound starter group(LSS)with Lactobacillus sakei and Staphylococcus xylose was significantly lower than that of the LS group(4.93)and the control group(CO)(5.38)(P ?0.05).At the end of ripening,the red color(22.48)of LSS group was significantly higher than that of LS and CO groups(P ?0.05).The decrease of pH value and aw,and the rapid increase of Lactobacillus and Staphylococcus significantly inhibited the number of Enterobacteriaceae in sausage.The number of Enterobacteriaceae in LSS and LS groups(2.35,2.36 log CFU/g)was significantly lower than that the CO(2.99 log CFU/g)(P ?0.05).The low number of Enterobacteriaceae led to the lower content of cadaverine,putrescine and histamine in sausage in the LSS than those in the CO.The decomposition of proteins in sausage was mainly concentrated in the fermentation and maturation at 0-5 d and was promoted by endogenous enzyme and starter.At the end of ripening,the PI of LS and LSS group was significantly higher than that of CO group(P ?0.05).The decomposition products of sarcoplasmic and myofibrillar proteins were mainly concentrated at the sites of 33-45 and 50 KDa.The addition of starter had a certain promoting effect on the activity of cathepsin B,which in LSS group was higher than that in the LS and CO at 0-5 d.the correlation between the protein value decomposition index and the activity of cathepsin B in CO,LS and LSS groups was 0.88,0.85 and 0.86,respectively,higher than that of cathepsin L,which can be seen that cathepsin B promoted protein degradation more significantly than cathepsin L.In the 2-8 d ripening process,the activity of aminopeptidase in the LSS showed an increasing trend,with an increase rate of 47.78%on the 5-8 d,and the enzyme activity was 6.69 U/mL,significantly higher than that in the CO(4.70 U/mL)and the LS(5.14 U/mL).The higher activity of aminopeptidase promoted significantly the content of free amino acids in the LSS(P ?0.05).At the end of ripening,the contents of essential amino acids and total amino acids in sausage of teh LSS(77.95,224.97 mg/100g)were significantly higher than those in the LS(67.20,179.04 mg/100g)and the CO(60.27,170.93 mg/100g).Moreover,the content of branched-chain amino acids(leucine,isoleucine and valine)in sausage of LSS group were higher than those of other two groups.And in terms of taste,the compound starter reduced the bitter and salty taste of the sausage and increased the umami taste of the sausages.The decomposition degree of phospholipids was higher than that of neutral lipids,and the contribution of phospholipids decomposition to free fatty acids was higher than that of neutral lipids.Based on the correlation analysis of phospholipids and neutral lipids with the formation of free fatty acids,it is found that the contribution of neutral lipids decomposed by starter cultures to the release of unsaturated fatty acids was higher than that of phospholipids,while the contribution of phospholipids decomposed by starter cultures to the release of saturated fatty acids was higher than that of neutral lipids.The contents of glycerol diester and monoglyceride of neutral lipid decomposition products in LSS group were not significantly different from those in the CO and LS(P? 0.05).The decomposition of neutral lipid and phospholipid in sausages were the highest at 2-5d and 0-5d respectively,and the increase of free fatty acid content was the biggest at 2-5d.The correlation coefficients of neutral lipase,phospholipase and fatty acid content in the two groups of CO and LSS were 0.95 and 0.92,respectively,which were higher than the correlation coefficient with acid lipase.It can be concluded that the promotion of neutral lipase and phospholipase on the formation of free fatty acid were significantly higher than that of the acid lipase.At the end of 5 days,the content of free fatty acid in the three groups was:LSS group(7.05 g/100g)>LS(6.97 g/100g)>CO(5.57 g/100g).The content of monounsaturated fatty acid(MUFA)was significantly higher than that of saturated fatty acid and polyunsaturated fatty acid(PUFA)(P<0.05),and the MUFA content of LSS group was significantly higher than that of CO and LS group.The increase of oleic acid content played a major role in the significant increase of MUFA content.The content of PUFA in LSS group was also higher than that in other groups,and the proportion of linoleic acid and linolenic acid was the highest.After fermentation and ripening,the kind of the flavor substances in sausage were significantly increased,and the relative contents of flavor substances were significantly increased by inoculating Lactobacillus sakei and Staphylococcus xylose.Flavor substances such as 2,3-butanediol,3-methylbutanal,hexanal,benzaldehyde,heptanal,1-octen-3-ol,ethyl acetate,etc.detected in the sausage have good odor,of which thresholds are 0.002,0.06,0.015,0.35,0.3,0.1 and 0.009 mg/kg and are significantly lower than those of other flavors(P<0.001).The content of the above flavors in the LSS group at the end of ripening were significantly higher than those of the LS and CO(P<0.05).In terms of flavor contribution,2,3-butanediol contributed the most to oil flavor of sausage,but heptanal was less;hexanal with green grass flavor and ethyl acetate with pineapple flavor contributed the larger to the flavor of sausage;3-methylbutyral-dehyde with fruit flavor and 1-octene-3-alcohol with mushroom flavor contributed the second to the flavor of sausage,while benzaldehyde with bitter almond flavor had relatively little impact on the flavor.It can be seen that the inoculation of compound starter has a significant effect on improving the flavor of sausage.The simulated bacterial strain metabolized leucine to form 3-methyl-butyraldehyde pathway,and it was known that Lactobacillus sakei and Staphylococcus xylose metabolized leucine to form 3-methyl-butyraldehyde by transamination and a-ketoacid decarboxylase(KADC)pathway.The pH value and salt concentration were in the range of 4.5-5.0 and 1.5-2.0%,respectively,which were helpful to increase the contents of hexyl aldehyde and 3-methyl butyraldehyde.To sum up,the compound starter of Lactobacillus sakei and Staphylococcus xylose can improve the activities of cathepsin,aminopeptidase,neutral lipase and phospholipase,promote the degradation of protein and lipid,increase the content of free amino acids and fatty acids,and make sausage nutrition more balanced.Through fermentation and ripening,the compound starter significantly increased the contents of 3-methyl-butyraldehyde and hexyl aldehyde,which contributed a lot to the flavor sense,and improved the taste and color of sausage.The compound starter promoted lactobacillus and staphylococcus to become the dominant bacteria group,significantly reduced the number of enterobacteria and the content of harmful amine and nitrosamine,and improved the safety performance of sausage.