| Dry sausage is a small-caliber sausage made of raw meat and flavoring agent through fermentation and air-drying dehydration,which has a unique flavor and taste.Lactic acid bacteria fermentation is an important technical means of dry sausage processing.The fat oxidation reaction during fermentation has an important influence on the quality and flavor of the product.Lactic acid bacteria can effectively control the degree of fat oxidation,improve the quality and flavor of dry sausage,and extend the shelf life.There is a common phenomenon of high cholesterol content in meat products,and excessive intake of cholesterol can easily lead to hypercholesterolemia such as atherosclerosis and coronary heart disease.By adding lactic acid bacteria with cholesterol-lowering function,the cholesterol content of dry sausage can be reduced and the health of the product can be improved.The process of microbial succession in naturally fermented dry sausage is complicated,and harmful bacteria such as pathogenic bacteria and spoilage bacteria multiply at will,so the final quality of the product is difficult to control.In this study,a lactic acid bacteria strain was screened from fermented food,which was suitable for meat starter and had high cholesterol-lowering performance.After in vitro physiological characteristics evaluation and 16 S r DNA sequencing identification,the strain(Lactobacillus paracasei Jlus66)was applied to fermented dry sausage(Jlus group),natural fermentation(Con group)and Lactobacillus plantarum SC-5 fermentation(SC group)were set for comparison.Samples were collected on the 0 th,3 rd,6 th,9 th and 12 th day of the fermentation process to explore the effects of starter on the physical and chemical properties(PH,moisture content,color,texture,TVB-N value and cholesterol content)and the degree of fat oxidation(POV value,TBARS value and antioxidant enzyme activity)of dry sausage.The types and relative contents of volatile flavor components and free fatty acids in dry sausage were detected by gas chromatography-mass spectrometry(GC-MS).High-throughput sequencing technique was used to monitor the succession of flora and microbial diversity during the fermentation of dry sausage,and the correlation between flora structure and volatile compounds was explored by Spearman correlation analysis.The results are as follows:(1)Effects of starter cultures on physicochemical properties and flavor components of dry sausage: The p H value and total volatile basic nitrogen content(TVB-N value)of Jlus group and SC group were significantly lower than those of Con group(P <0.05),and the texture and color indexes were superior to those of Con group.The degradation rates of cholesterol in dry sausage by Lactobacillus paracasei Jlus66 and Lactobacillus plantarum SC-5 reached 36.56±0.85% and 20.65±0.94% respectively.Lactobacillus plantarum SC-5 has stronger acid-producing ability,while Lactobacillus paracasei Jlus66 has stronger cholesterol-lowering ability.The types and relative contents of esters in each group increased significantly,while the types and relative contents of alkanes decreased significantly.Both Lactobacillus paracasei Jlus66 and Lactobacillus plantarum SC-5 affected the release of volatile compounds.On the 12 th day of fermentation,the types and relative contents of esters,terpenes and aromatic hydrocarbons were the highest in Jlus group,while the relative contents of alcohols and aldehydes were the highest in SC group.(2)Effect of starter cultures on lipid metabolism of dry sausage: The relative contents of monounsaturated fatty acids and polyunsaturated fatty acids in Jlus group and SC group were higher than those in Con group,while the relative contents of saturated fatty acids were lower than those in Con group.The results showed that Lactobacillus paracasei Jlus66 and Lactobacillus plantarum SC-5 were beneficial to the formation of unsaturated fatty acids which were easier to decompose,and promoted the formation of flavor substances and aroma precursors.The peroxide value(POV),thiobarbituric acid reactant content(TBARS value)and antioxidant enzyme activity in Jlus and SC groups were significantly lower than those in Con group(P < 0.05).Compared with SC group,the POV value and TBARS value of Jlus group were significantly lower than those of SC group,and the CAT activity and GSH-PX activity were significantly higher than those of SC group(P < 0.05),which indicated that Lactobacillus paracasei Jlus66 had a better antioxidant effect.(3)Analysis of microbial diversity: high-throughput sequencing results showed that the flora diversity in the sample was the highest on the 0th day and the lowest on the6 th day,and the microbial community structure of the sample tended to be single during the fermentation process.In all samples,Firmicutes is the dominant phylum,and Lactobacillus is the dominant genus.On the 12 th day of fermentation,the relative abundance of pathogenic bacteria such as Acinetobacter and Enterococcus in Jlus group and SC group was lower than that in Con group.The results of LEf Se difference analysis and Barplot difference analysis showed that the abundance of Lactobacillus in Jlus group was significantly higher than that in Con group and SC group.The abundance of Enterococcus,Streptococcus,Acinetobacter,Escherichia,Citrobacter and other miscellaneous bacteria was significantly lower than that of Con group.Thermogram analysis showed that Jlus group had the lowest bacterial abundance.The results showed that Lactobacillus paracasei Jlus66 had obvious antagonistic effect on spoilage bacteria and pathogenic bacteria.Spearman correlation analysis of Top15 bacteria and volatile compounds showed that Lactobacillus was the main bacteria affecting volatile compounds,and it was positively correlated with many volatile compounds such as oleic acid,phenylethanol,styrene,succinic acid,diethyl ester,ethyl isocholate and so on.In conclusion,Lactobacillus paracasei Jlus66 can effectively improve the quality and flavor of dry sausage,which provides a theoretical basis for the processing of fermented dry sausage with low cholesterol and high quality. |
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