The Research On The Flavour Characteristics Of Fermented Capsicum

Fermented pepper is one of the most popular fermented vegetables,and its flavour is the key to attracting consumers.This study prepared 14 single-and double-strain fermented pepper samples under low-salt(1%)conditions,the physiological and biochemical characteristics of the samples were analyzed,and the effects of inoculation with lactic acid bacteria and yeast on the microbial community and volatile compounds in fermented peppers were revealed.Key flavour compounds were identified and their regulatory mechanisms were revealed.The main findings are as follows:(1)Physicochemical indicator analysis showed that the acid-producing ability of QB3 was strong,and it had a positive effect on the improvement of some nutrients;the C.rhodanensis J52 consumed less reducing sugar during fermentation,and its co-fermentation with P.pentosaceus(AL)helped to increase the VA content of fermented pepper.In 14 samples,there was no significant change in total acid content.(2)Microbial diversity analysis showed that 158 bacteria and 55 fungi were detected in fermented pepper,and QB3,AL,AD,J52,and M4 could occupy a growth advantage during fermentation.AL could inhibit the growth of pathogenic bacteria such as Enterobacter,Klebsiella,and Enterococcus,and it had a strong inhibitory effect.It had a good symbiotic relationship with J52,which was beneficial to the fermentation of pepper.(3)89 volatile compounds were detected during pepper fermentation,and esters were the main substances affecting the flavour.The key strains that affected the flavour after fermentation were Ky with AL,J52 with AL,M4 with AS,and QB3,and the effect of double-strain fermentation on the flavour was greater than that of single-strain fermentation.The key compound affecting the flavour was isoamyl acetate,whose odor activity value was greater than 1 and fold change(Fold change,FC)reached 151.51.The correlation analysis between microorganisms and compounds revealed that C.rhodanensis J52 is a key strain for producing isoamyl acetate,while lactic acid bacteria have a stronger negative correlation with the compound and are weaker in terms of flavour improvement compared to yeast.(4)The medium composition and culture conditions of J52 strain were optimized using a single factor combined response surface methodology.The PB test results showed that the inoculation amount,fermentation time,yeast extract addition amount,and p H significantly affected the concentration of isoamyl acetate.The response surface analysis results showed that the maximum isoamyl acetate content of51.3 μg/m L was achieved when the inoculation amount was 1×〖10〗^(23?4)CFU,fermentation time was 24 h,and yeast extract addition amount was 1.61%,with an actual yield of 52.41 μg/m L.(5)Transcriptome analysis of the J52 strain before and after optimization of the culture medium showed that Gene TRINITY＿DN4654＿c0＿g1(NR annotation:Pyruvate dehydrogenase [acetyl-transferring]-phosphatase 2),TRINITY＿DN582＿c1＿g1(NR annotation: ONH68203.1 protein)and TRINITY＿DN1840＿c0＿g2(NR annotation: AAK54236.1 protein)along with 23 other genes associated with them may regulate the synthesis of isoamyl acetate.