| Instant fresh rice noodles are the staple food of many people in the south of China.Rice were common pre-processed by natural fermentation.But it is a hardly control process where spoilage and pathogenic organisms bred.Therefore,the noodles general had a long fermentation process and a short shelf-life.Thus,it has important significance to promote the industrial control production of instant fresh rice noodles.In this paper,changes in the physicochemical characteristics of rice and bacterial community structure dynamics during the natural fermentation process of rice noodles were investigated.And a preliminary exploration on the preparation of rice noodle starter was conducted.The paper demonstrated that just rice soaked by water(microbes were inhibited)can't significantly alter its chemical content.And the instant fresh noodles developed by soaked rice had significant lower tensile strength,hardness,cohesiveness,and higher adhesiveness than by natural fermented rice.The paper also indicated that natural fermentation can significantly change the physicochemical characteristics of the rice.And the changes mainly happened at the early stage of the fermentation process(Day 1).Further chemical content changes in the subsequent phase of fermentation were observed to be only slight.Specifically,total starch contents increased from 74.39% to 80.87% and amylose from 20.47% to25.26%.In contrast,crude lipid decreased from 1.82% to 1.39%,crude protein from9.72% to 4.78%,ash content from 0.58% to 0.27%.In addition,significant changes at the molecular level were also observed including that the major subunits of protein fraction at 19.2 k Da and 31.9 k Da disappeared and that some breakdown in the starch granules took place.The changes of protein fractions was as some as crude protein.Briefly,albumin contents decreased from 0.10% to 0.05%,globulin from1.16% to 0.48% and glutelin from 5.08% to 1.96%.But prolamin content hadn't significant changes.Further physicochemical characteristics changes in the subsequent phase of fermentation were observed to be only slight.The bacteria community structure dynamics during fermentation were detected by high-throughput sequencing(Illumina Miseq sequencing).Lactic acid bacteria(LAB)were seen to be the dominant bacteria(above 90%)during the entire process.In the subsequent phase of fermentation,LAB were above 99%.The relatively high abundance of Lactobacillus fermentum and Lactobacillus delbrueckii at each phase of the fermentation suggests that the two species are the fastest growing and property-determining species in the rice fermentation process.Aims to prepare a starter for the manufacture of instant fresh rice noodles,the potential strains of micro-organisms were selected from the rice natural fermentation process.Overall,41 strains of yeast and 60 strains of lactic acid bacteria(LAB)were isolated during the traditional fermentation process of rice noodles.In the first experimental phase,the technological traits—enzymatic activities(catalase,?-glucosidase,lipase,?-amylase,proteolytic enzyme),growth under various conditions of pH and temperature,acidification capability,and antimicrobial activities—were characterized.Principal component analysis of the results indicated that 11 strains of yeast and 19 strains of LAB exhibited better technological traits.In the second experimental phase,these selected isolates were then identified by the internal transcribed spacer(ITS)sequence for yeasts and the 16 S rRNA gene for LAB,which grouped them into three strains of yeast and four strains of LAB by their genotypes and phylogenetic trees.In the final experimental phase,these seven species were used as starters for preparing rice noodles.The resulting textural(tensile strength,hardness,adhesiveness,and cohesiveness)and cooking qualities(cooking loss and cooked weight)of the rice noodles showed that two potential isolates of Saccharomyces cerevisiae strain CSY 13 and Lactobacillus plantarum strain CSL 23 were most suitable as starter cultures for preparing rice noodles. |
PDF Full Text Request