Analysis Of Flavor Component Of Fermented Rice Noodles And The Screening And Application Of Potential Strains

Rice noodles is a typical fermented food,which was popular in Southwest China and Southeast Asia,and it is even consumed as a staple food in Guilin,China.Fermentation is important in the manufacture of fermented rice noodles,and the purposes of fermentation is to improve the processing properties and reduce the stickiness of rice dough,meanwhile,enrich the products with better mouthfeel and unique flavors.However,as spontaneous fermentation is still adopted widely,microbial contamination and unpleasant smell are serious problems during the fermentation,and these problems not only increase the cleaning cost but also bring the risk of food safety.At present,the research on fermented rice noodles is limited,and the flavor formation mechanism has been rarely reported.Therefore,an in-depth study of flavor formation mechanism in rice fermentation can provide theoretical guidance for the screening of ideal strains for fortified fermentation,as well as the optimization of the production process of fermented rice noodles.In this paper,a typical fermented rice noodles was taken as the research object,and flavor analysis and microbiology analysis were carried out systematically to find the microorganisms related to the key flavors,thus,the fortified fermentation process could be established based on them.Main contents of this paper are as follows:Firstly,the key flavor of Guilin samples were found out.Results of GC-MS and GC-MS-O showed that alcohols and acids were the main flavors.During the fermentation,the contents of alcohols(especially ethanol)increased firstly,and then decreased,while the contents and varieties of acids kept accumulating all the time.Hereinto,ethanol,isoamyl alcohol,acetoin,acetic acid and 2-phenylethanol are revealed to be the key flavors,with flavor intensity up to 2.In addition,seven biological amines were detected,especially tyramine,putrescine and histamine,which possessed relative higher contents compared with the others,although,they did not significantly affect the flavor,they increased the food safety risk.Secondly,the roles of microorganism in the synthesis of key flavor substances the key flavor of Guilin samples were clarified.Amplicon sequencing analysis showed that the dominant microorganisms in the fermentation were lactic acid bacteria,when Weissella,Lactococcus,Pediococcus,Leuconostoc,Lactobacillus,Acetobacter and Aspergillus were dominant bacteria.Correlations between microorganisms and flavors were analyzed based on the changes of them,combined with the results of gene function annotation.Lactobacillus,Acetobacter and Lactococcus were suggested to be the producers of key flavors,especially Lactobacillus,possessed the greatest application potential,for the synthesis potential of ethanol,acetic acid,isoamyl alcohol and 2-phenylethanol.Finally,a L.Fermentum with potential application in the flavor fermentation were screened and the related fermentation technology was established.Four Lactobacillus species were isolated from Guilin samples,including L.brevis,L.casei,L.plantarum and L.fermentum.They were applied in the fortified fermentation of rice noodles,concentrated on the flavor,harmful microorganism,and texture of fermentation,and a brand-new fermentation process was established using the optimal strain as the starter.It was found that the fermented products of L.plantarum(Group L.p)and L.fermentum were preferred for flavors,because 1-octen-3-ol and acetic acid gave them additional umami and pleasant acerbity,while 3-methylbutyric acid brought unpleasant sour smell to samples fermented spontaneously.Hereinto,Group L.p got the highest score,for its compound flavor contained all the above key flavors;while superior ability of L.fermentum to produce acetic acid,made it able to inhibit mold and pathogenic bacteria(Enterobacter and Cronobacter).As L.fermentum possessed both great flavor and antibacterial activity,fortified fermentation of L.fermentum was optimized systematically later,corresponding conditions were confirmed as follows: the fermentation form was solid-state fermentation(powdery),the inoculum volume was 1.0%(v/w),the fermentation temperature was 30?,the fermentation time was 3 d;then,by adding 0.20%(w/w)sodium carbonate,the acid taste of fermented products could be effectively removed,thus simplifying the production process and improving the production efficiency.In the end,product made by the new process was proved to have greater cooking quality,mouthfeel and flavor(p < 0.05),compared with controls.