| Lactic acid bacteria(LAB)are often used in the production of fermented meat products.The physiological characteristics of fermented strains will directly affect the quality of fermented products.Previous studies have been confirmed that LuxS/AI-2quorum sensing(QS)system is closely related to the functional characteristics of LAB.However,studies on the fermentation characteristics of LAB in meat products based on the activity of the QS signal molecule AI-2 are rarely reported.In this research,a strain of Limosilactobacillus fermentum 332,which had the potential to fermentate meat products,was selected as the research object.Firstly,the fermentation function characteristics of the L.fermentum 332 and the activity of signal molecule AI-2 were measured.Secondly,Based on the single factor experiment,the fermentation parameters of the strain were optimized by orthogonal experiment.And the activity changes of signal molecule AI-2 were also explored.Finally,the strain was inoculated into mutton for fermentation,and the difference of fermented sausage quality between adding signal molecule AI-2,without adding signal molecule AI-2 and natural fermentation was compared.The change of quality characteristics of fermented mutton sausage with the addition of signal molecule AI-2 was explored.It lays a theoretical foundation for improving the production performance of fermentation strains and product quality in food industry.The results are as followed:(1)The activity of L.fermentum 332 signal molecule AI-2 was positively correlated with the acid production ability.In the logarithmic phase,the strain produced acid rapidly,with a fermentation broth p H of 4.16 and the highest activity of the signal molecule AI-2.At the same time,the EPS production capacity of L.fermentum 332 was the highest at the logarithmic stage(13 h),with exopolysaccharides(EPS)production up to 358±1.9 mg/L,which was positively correlated with the activity of signal molecule AI-2.However,after the stable stage,the activity of signal molecule AI-2 decreased,and the EPS and acid production tended to be stable.(2)The optimal process conditions for fermented L.fermentum 332 in fermented sausage were determined.The optimal fermentation conditions were inoculation quantity of 5%,fermentation temperature of 30℃,and fermentation time of 30 h.At this time,the p H value and titratable acidity of the fermented sausage were 4.66 and 0.913 g/kg,respectively.The activity of signal molecule AI-2 was measured under different fermentation condition parameters.The results showed that inoculation amount and fermentation temperature were positively correlated with the activity of signal molecule AI-2.With the extension of fermentation time,the activity of signal molecule AI-2 first increased and then slowly decreased.The highest activity of signal molecule was observed after 15 h of fermentation.(3)The quality changes of fermented mutton sausage were studied by adding L.fermentum 332 as test group 1 and adding exogenous signal molecule AI-2 and L.fermentum 332 as test group 2,taking natural fermentation as control group.Adding exogenous signal molecule AI-2 to culture L.fermentum 332,The growth and acid yield of L.fermentum 332 were significantly promoted under the addition of 50 μmol/L AI-2(p <0.05).L.fermentum 332 and 50 μmol/L exogenous signal molecule AI-2 were inoculated into mutton sausage to determine the quality changes of fermented mutton sausage.The results showed that the viable number of LAB in fermented sausage inoculated with L.fermentum 332 and AI-2 was significantly higher than that of only inoculated with L.fermentum 332 and control natural fermentation(p < 0.05)with the viable count of9.47±0.02 lg CFU/g.The p H and Aw value of fermented sausage after fermentation period were significantly decreased(p < 0.05)in test group 2;In the meanwhile,the entire processing stage improved the brightness value of fermented sausage,thereby improving the color of fermented sausages.Compared to the control group,the hardness,elasticity,and chewiness of fermented sausages in experimental groups 1 and 2 increased.Meanwhile,during the fermentation period,the TVB-N and TBARS values of fermented sausages in test group 2 were 7.933 mg/100 g and 0.08 mg/100 g,respectively,significantly lower than those in the control group.The types and contents of fermented sausage flavor substances in test group 2 were significantly higher than those in control group The contents of 2-butanol,butyl propionate,isoamyl acetate,butanol,α-pinene,isobutyl acetate and butyl acetate were significantly increased.Compared with test group 1,the types of volatile flavor substances in test group 2 were similar but the contents of volatile flavor substances were higher,especially amyl alcohol and acetic acid.Therefore,the quality of fermented mutton sausage was improved partly by the addition of L.fermentum 332 and signal molecule AI-2. |
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