Analysis Of The Main Characteristics Of Sichuan Paocai And Its Formation Mechanism

Sichuan paocai is one of the representatives of traditional fermented vegetable in China.It is favored by consumers due to its distinct organoleotic quality.Generally,there are two methods for paocai production,i.e.,the saline paocai and the old brine paocai.The unique flavor of Sichuan paocai depends on old brine.The old brine is often obtained by recycling the brine time after time,which limited its application in industrial production due to the long recycling time.Although abundant research has reported that the taste of old brine paocai is better than saline paocai,the taste characteristics of old paocai brine is still unclear.Microorganisms is closed related to tastes of paocai.While the microorganism characteristics and its correlation with the formation of characterisitic tastes compounds is unknown.Therefore,to resolve the above question the physiochemical characteristics and distinct tastes compounds of Sichuan paocai were first investigated in the present study.Then the microorganism structure of sichuan paocai and related influnencing factors were studied.Thirdly,the formation mechanism of microorganism in sichuan paocai were illumited by establishment of modeling system which reconstructed the microorganism structure of paocai.Finally,the correlation of core microorganisms with taste compounds of sichuan paocai is illustrated by modeling system.The main results are as follows:1.To clarify the predominant physicochemical parameters and taste compounds of Sichuan paocai,50 paocai fermented by different aged brine at different place were collected and examined.The pH was 3.73;the content of salinity,total sugar,total acid and total nitrogen was 7.02 g/100 g,235.84 ?g/g,12.34 mg/g and 1.60 mg/g,respectively.20 non-volatile compounds was identfied as predominant non-volatile compounds in Sichuan paocai.Compared the predominant physicochemical parameters and non-volatile compounds of different Sichuan paocai,the results showed that product place of Sichuan paocai had no significantly effect on predominant physicochemical parameters and non-volatile compounds of paocai.The total acid and total nitrogen contents were significantly higher in the aged brine paocai(over 10 years old)than in paocai fermented by brine that used less than one year.The structures of taste substances of over one year aged brine paocai were different from aged brine paocai that was used for less than one year.2.To describe the microbial flora of paocai,100 Sichuan paocai brine were analyzed by high-throughput sequencing and multivariate statistical analysis.The results showed that the predominant microbiota of salt brine were different from that of old paocai brine.The predominant microbiota of salt brine is Leuconostoc,L.and Lactobacillus,whereas that of the old paocai brine is Lactobacillus and Pediococcus.The regions,vegetables and water of paocai had no significant effects on the paocai flora.The season of paocai production had influenced the microbial flora.The osmotic pressure,sodium chloride content,total acid content and total nitrogen content of paocai brine,which were positive correlated with the time of recycling brine,had a significant effect on the composition of brine flora.The total acid content had the strongest predictive effect on the microbial flora of paocai brine.The brine were therefore divided into low acid brine and high acid brine.Besides,the brine pH values and total sugar content had no significant effect on the structure of the brine flora.3.To further investigate the formation of core bacterial diversity,the core bacterial communities was identified by high-throughput sequence and culture-independent method.The results showed that Lactobacillus plantarum,Leu.mesenteroides,Lactococcus.lactis was the core bacterial communities of salt paocai brine,and L.plantarum,Pediococcus ethanoltolerans and L.buchneri was the core bacterial communities of old paocai brine.In the paocai brine model system without lactic acid,the increasing salt content had an inhibitory effect on the growth of La.lactis and Leu.mesemteroides.When co-cultured,L.plantarum inhibited the growth of Leu.mesemteroides and La.lactis.La.lactis also has a certain inhibitory effect on the growth of Leu.mesenteroides.In the paocai brine model system with lactic acid,Leu.mesemteroides and La.lactis almost did not grow normally.The high lactic acid content had a strong inhibitory effect on Lb.plantarum,while the inhibitory effect on Ped.ethanoliduran and L.buchneri was weak.At the same time,P.ethanoliduran promoted the growth of Lb.plantarum and Lb.buchneri.4.To clarify the marker taste compounds of Sichuan aged brine paocai,saline paocai and aged brine paocai fermented by paocai brine used over ten years were examined and compared.The results show that the taste characteristics of old brine paocai are totally different from that of the saline one.Aged paocai brine affects the tastes of paocai,including umami,saltiness,bitterness,and aftertaste astringency,whereas sourness was the major characteristic of SB-paocai.Moreover,there are significant differences in the non-volatile and volatile substances between the saline and the aged brine paocai.18 marker non-volatile taste compounds such as glutamic acid,4-aminobutyric acid are significantly higher in the aged brine paocai than in the saline paocai.Compared to saline paocai,the aged brine paocai has significant lower contents of five sulfide such as the methyl mercaptan and the dimethyl disulfide and higher contents of eight substances.The eight substance are as follows: ethyl acetate,Propionate,methyl salicylate,acetic acid,propionic acid,2,4-dienal,benzaldehyde and 2-butenenitrile.In the paocai brine model system with lactic acid,the effect of different old brine core microorganisms on marker non-volatile compounds was different.L.plantarum could significantly increase lactic acid,glycine,4-aminobutyric acid,succinic acid,5-oxo-proline and mannitol.L.buchneri could significantly increase lactic acid,glycine,glutamic acid,4-aminobutyric acid,5-oxo-proline and mannitol.Ped.ethanoltolerans could significantly increase 5-oxo-proline and lactic acid.Inoculated core microbiota of old paocai brine could significantly increase the level of 5 marker taste compounds such as mannitol,lactic acid and glutamic acid.During the paocai fermented,inoculated core microbiota could significantly increase 6 marker taste compounds such as mannitol,lactic acid and glutamic acid.