Study On The Fermentation Of Indica Rice Flour Slurry By Lactobacillus And Yeast And The Preparation Of Fermented Rice Cake

In this study,3 from 5 strains of lactobacillus was chosen,which can produce amylase.The ability of producing amylase and fermenting indica rice flour slurry was studied,further studying the flavor compounds produced by lactobacillus one-strain fermentation and twostrain fermentation that mix with yeast,then the most suitable lactobacillus&yeast for the fermentation of indica rice flour slurry was chosen,which could be used to produce fermented rice cake.Through the response surface method,the best fermentation parameters was explored,which can provide a theoretical basis for the two-strain fermentation of fermented rice cake by lactobacillus and yeast.The main results of the study are as follows:(1)L.acidophilus 14(LA),L.casei M(LC)and L.plantarum 115(LP)were found to be capable of amylase production in five strains of lactobacillus by starch medium screening.These lactobacillus were used to establish the lactobacillus-indica rice flour slurry fermentation system.The starch content,pH value and amylase activity in the system before and after fermentation were investigated.It was found that the ability to degrade raw starch ranked as LA>LP?LC,the growth rate ranked as LA>LP>LC,and the acid-producing ability ranked as LA>LP?LC.(2)After the extraction of crude enzyme solution,the enzymatic characteristics were determined,found that three amylase produced by lactobacillus,LA-amylase(LA-a),LC-amylase(LC-a)and LP-amylase(LP-a),optimum temperature were in 45~55 ?,which all cannot tolerate high temperature above 70 ?.All three were neutral enzymes,and their acid and alkali resistance ranked as LA-a>LP-a>LC-a.After fermentation,the proportion of amylose in total starch increased,indicating that there was a certain amount of isoamylase in the amylase produced by lactobacillus.(3)Headspace solid-phase microextraction(SPME)coupled with gas chromatographymass spectrometry(GC-MS)was used to analyze the flavor compounds in the fermented indica rice flour slurry.After 6 h fermentation of LA,the main flavor compounds were lactic acid and 3-hydroxyl-2-butanone,which brought the milk flavor.After 12 h fermentation of LA,2-methyl-butyric acid,hexanol,2,3-butanediol and hexyl formate were produced,which contributed to sweet,cheesy and fruity flavors.After 6 h fermentation of LC,lactic acid,acetic acid,3-hydroxy-2-butanone,isovaleraldehyde and formic acid ester was produced,the system had a certain irritant smell,milk and fruit flavor.After 12 h,butyric acid,3-methyl butyric acid,2-butanone was produced,and there was no isovaleraldehyde,the system had cheese flavor and strong irritant smell.After 6 h and 12 h fermentation by LP,only acetic acid was presented.To sum up,LA was the best strain for one-strain fermentation of indica rice flour slurry.(4)Regardless of the large amount of ethanol in the system,the main flavor compounds in the lactobacillus mixed yeast(Y)fermented indica rice flour slurry were carboxylic acids,alcohols and esters.The main flavor compounds after 6h fermentation of LA+Y are formic acid,isoamyl aldehyde,isoamyl alcohol,isoamyl formate and ethyl acetate,which brought fruit flavor and sweet flavor.After 12 h fermentation of LA+Y,alanine and phenyl ethyl acetate were produced,the sweet flavor of the slurry was more obvious.After LC+Y fermentation for 6 h,the main flavor compounds were alanine,formic acid,isoamyl alcohol,isoamyl formate and phenylethyl caproate,which gave the indica rice slurry a strong sweet taste,with a little milk flavor and fruit flavor.After another 6 h fermentation,isoamyl aldehyde was produced,enhancing the fruit flavor.After 6 h fermentation by LP+Y,the main flavor compounds was formic acid,isovaleraldehyde,isoamyl alcohol,formic acid isoamyl acetate and ethyl acetate,the system has certain acidity and irritant smell,sweet and fruit flavor.After another 6 h fermentation,ethyl butyrate,isoamyl butyrate and phenyl ethyl butyrate was produced,the indica rice slurry had strong fruit and sweet flavor,irritating smell was weak,and it contained a weak cheese flavor,the system had the best smell at that time.To sum up,LP+Y is the best two-strain to ferment indica rice flour slurry.(5)Using sensory evaluation and TPA texture test,found that the best value of rice cake hardness was close to 2700 g,the best value of springiness was close to 0.75,the best value of resilience was close to 0.25,and the best value of gumminess was close to 1000.(6)The response surface method was used to establish the regression equation,and the interaction effect between the fermentation parameters was analyzed.Fermentation time,fermentation temperature and inoculation quantity all have great influence on the texture characteristics.The interaction between fermentation time and fermentation temperature was not significant,and the interaction between inoculation quantity and fermentation time or temperature was significant,so the inoculation quantity is the most critical factor affecting the texture in the fermentation process.Taking the optimal value of each texture as the target value and combining with the regression equation,the best fermentation technical parameters was as follows: inoculation quantity was 0.16%,fermenting under 37 ? for 6 h.