Screening Of Starch Flocculating Bacteria And Its Effect On Properties Of Pea Starch

Microbial fermentation of sour liquid method is a traditional method to produce pea starch,mung bean starch and sweet potato starch in China.On the one hand,pea sour liquid plays the role of flocculation to promote the settlement of starch,on the other hand,in the process of starch flocculation,by changing the properties of starch,and then improve the processing properties of vermilion.The traditional Longkou vermicelli in China is produced by microbial fermentation sour liquid method,which has the characteristics of good quality and bright color,but the influence of microbial fermentation on the processing properties of pea starch is still unclear.Therefore,the application of sour liquid method in vermicelli processing is limited.This study took pea sour liquid naturally fermented by microorganisms as the research object,analyzed the microbial composition of pea sour liquid through high-throughput sequencing technology,combined with traditional microbial isolation and culture technology,identified strains with high flocculating starch activity and optimized their growth and flocculation conditions,and analyzed the flocculation properties and the structure and physical properties of pea starch treated by flocculating bacteria at different fermentation times.It lays the theoretical foundation and technical reference for the industrial production of pea starch by the fermentation of pea sour liquid by pure microorganism and the development of special microbial flocculant and biomodified starch.The main research contents and results are as follows:1.The microflora of naturally fermented pea sour liquid was analyzed by high throughput sequencing technology.Two groups of samples,pea sour liquid and precipitated starch,were extracted for abundance analysis.The results showed that the bacterial richness and diversity in the sour liquid group were higher than that in the precipitated starch group.At the phylum level,the Proteobacteria of the sour liquid group accounted for 56.92%of the dominant phylum;the Firmicutes in the precipitated starch group accounted for 55.84%of the dominant phylum.At the genus level,the Acetobacter of the sour liquid group accounted for 55.70%of the dominant bacteria;the Lactobacillus in the precipitated starch group accounted for55.60%of the dominant bacteria.2.Isolation,screening and identification of starch flocculating bacteria from pea sour liquid.Six strains with high flocculating starch activity were isolated and screened from sour liquid and precipitated starch by plate separation method with flocculation rate as index.Among them,the strain LJ5 had the highest flocculating activity in pea juice medium.Combined with the individual and group morphological characteristics,physiological and biochemical experiments and 16S r DNA sequence identification,the strain LJ5 was identified as Schleiferilactobacillus harbinensis and named as Schleiferilactobacillus harbinensis LJ5.3.Growth characteristics and growth curve determination of S.harbinensis LJ5.The single factor and response surface experiments were carried out on the growth conditions with the cell density（OD value）as the index.The optimum growth conditions of S.harbinensis LJ5 in the pea juice medium were as follows:fermentation temperature 35℃,inoculation amount 6%,initial p H 6.0,sucrose as carbon source,sucrose addition amount 3%,yeast extract powder as nitrogen source,yeast extract powder addition amount 0.5%.The growth curve of the bacteria was determined under the optimal growth conditions.The bacteria entered the logarithmic growth phase after 4 h,entered the stable phase after 24 h,and began to enter the decline phase after 58 h.The optimal growth time of S.harbinensis LJ5 was 24 h,and the number of viable bacteria was 8.31±0.03 lg CFU/m L.4.Optimization of flocculation conditions and analysis of flocculation properties of S.harbinensis LJ5.The flocculation conditions were tested by single factor and response surface test with flocculation rate as index.The optimum flocculation conditions of S.harbinensis LJ5 were obtained as follows:culture time 36h,culture temperature 35℃,flocculant dosage 6%,fermentation broth p H6.0.Flocculation properties analysis of S.harbinensis LJ5 showed that the flocculation factor may be a protein substance on the surface of bacterial cells,and Na⁺can be selected as a coagulant aid.5.Effects of S.harbinensis LJ5 fermentation on the properties of pea starch.With the extension of fermentation time,the crude fat content decreased gradually,the crude protein and ash content increased gradually,while the amylose content increased first and then decreased slightly.Fermentation increased the relative crystallinity of starch,decreased the relative proportion of long chain（B₂+B₃chain）and the intensity of infrared absorption peak.Pea starch is still C-type crystal structure.Scanning electron microscopy showed that the longer the fermentation time,the greater the degree of surface erosion of starch granules was observed.Fermentation increased the retrogradation,solubility and swelling power of pea starch.Fermentation makes pea starch granules loose and porous,reduces the gelatinization temperature,makes it easier to be gelatinized,has higher disintegration value,final viscosity and retrogradation value in the gelatinization process,and has higher hardness,elasticity and chewiness in the gel process.These texture characteristics are favorable characteristics of high-quality fans.