| In recent years,Lentinus edodes（L.edodes）cultivation has developed rapidly and the annual output has exceeded 10 million tons in China,making it the edible mushroom with the highest output in my country.However,the technological level of L.edodes processing is relatively backward in China,which restricts the healthy and sustainable development of the L.edodes industry.The use of Lactic acid bacteria（LAB）in fruit and vegetable fermentation can improve the flavor and nutritional value of products,but there are few reports on its application in L.edodes.This thesis using L.edodes as experimental materials,by researching the LAB fermentation properties of L.edodes,the LAB strains suitable for the fermentation of L.edodes were screened out,and the fermentation process conditions were optimized.Developed seasoned fermented L.edodes and LAB powder products,and studied the regulation of intestinal flora of the products.In order to provide a useful reference for the application of LAB fermentation technology in the deep processing of L.edodes.The main results are as follows:1.Study on the fermentation properties of Lactic acid bacteria Lentinus edodes and strain screeningThrough analysis and comparison of Streptococcus thermophiles（St）,Lactobacillus brevis.rhamnous（Lbr）,Lactobacillus casei（Lc）,Lactobacillus plantarum（Lp）,Lactobacillus brevis（Lb）and Lactobacillus brevis.fermentum（Lf）growth status and acid production of six common commercial LAB in L.edodes.The research results as follows: except for St,which grew slowly in the early stage,other strains entered the logarithmic growth phase after 8 hours,and the growth conditions were better in L.edodes.From the perspective of fermentation performance,except for the slightly weaker acid-producing ability of Lp,other strains had stronger acid-producing ability in L.edodes.As the fermentation time progresses,the p H value gradually decreases and the total acid content gradually increases.From the perspective of temperature resistance characteristics,the suitable temperature range for the growth of LAB is 25-40 ℃,of which Lb has better temperature resistance characteristics,and a large number of bacteria still grow at the fermentation temperature of 45 ℃.From the perspective of salt tolerance,a large number of LAB can tolerate 4% salt concentration.Among them,Lbr has better salt tolerance and can still moderate grow under10% salt concentration.Through screening,Lb,Lp and Lbr were selected as LAB suitable for the fermentation of L.edodes.By analyzing and comparing the p H value,total acid content and free amino acid content of fermented L.edodes and the compound experiment of the three kinds of bacteria was carried out.The compounding ratio is Lb : Lp : Lbr=3:1:2.2.Optimization of fermentation conditions of Lentinus edodes Lactic acid bacteriaUsing compound LAB species Lb : Lp : Lbr（3:1:2）to ferment L.edodes,the effects of fermentation temperature,salt addition and LAB inoculum on p H value,total acid content,free amino acid content and sensory score of fermented L.edodes were studied.The response surface optimization was carried out on the basis of single factor experiment,and the optimal fermentation conditions were obtained as follows: fermentation temperature 37 ℃,salt addition 1.0%,compound LAB inoculum 2.7%,fermentation time 48 h.The volatile components in L.edodes before and after LAB fermentation were compared.The results showed that the volatile components in fermented L.edodes were higher in acid,ketone,hydrocarbon and sulfide,which respectively were 2.2%,17.8%,1.78%,and 13.92%.After fermentation by LAB,the relative contents of acids（acetic acid）and ketones（2-heptanone,3-octanone,2-nonanone,methylnonyl ketone）in L.edodes respectively increased 2.16% and 17.8%,while the relative contents of alcohol,aldehyde and phenol were decreased by 3.66%,7.42% and 3.87%.The results show that the flavor of L.edodes can be significantly improved by fermentation,and the balance between flavor substances has an important influence on the flavor formation of fermented L.edodes.3.Research and development of Lactic acid bacteria fermentation products of Lentinus edodesThe L.edodes are fermented by using compound LAB species Lb : Lp : Lbr（3:1:2）,the fermented L.edodes pieces are made into seasoned L.edodes products through the seasoning process,and the L.edodes fermented liquid is comprehensively utilized and made by spray drying technology LAB powder.Through research,the best process conditions for obtaining flavored fermented L.edodes products are84.0% fermented L.edodes,1.0% sweet noodle sauce,1.5% bean paste,6.0% white sugar,3.0% rattan pepper oil,2.0% sesame oil,4.0% chili oil,ginger juice 1.0%,after mixing the raw and auxiliary materials evenly,it was prepared into a product of 15 g/bag,which was sterilized at 121 °C for 15 minutes and then subjected to a constant temperature accelerated test.The measured shelf life of the product under normal temperature conditions can reach 97 days.The best preparation process of LAB powder is dilute the L.edodes fermentation broth with water（fermentation broth: sterile water = 3:7）,then add 8% maltitol and20% maltodextrin in the total volume of the L.edodes fermentation broth,and stir evenly.Spray drying was carried out,the inlet air temperature was 117 °C,and the feed rate was 12 m L/min.The powder collection rate was 83.16%,the moisture content was 3.93%,and the number of viable bacteria was 10.40 log CFU/g.4.The regulatory effect of fermented L.edodes products on the intestinal flora of miceTo study the regulatory effect of LAB fermented L.edodes pieces and LAB powder on the intestinal flora of mice.After 4 weeks of gavage,fermented L.edodes products had no significant effect on the weight gain of mice.By 16 S r RNA high-throughput sequencing analysis of the intestinal flora of mouse colon contents,the species diversity,species composition at each taxonomic level and changes in relative abundance were studied.The results of ASVs clustering and diversity analysis showed that the fermented L.edodes products changed the species diversity of the intestinal flora of mice,the number of endemic and rare species increased,the individual differences of species diversity within the treatment group decreased,and the species distribution increased evenly.In terms of species composition,the dominant intestinal flora in the control group and all treatment groups belonged to the two phyla Firmicutes and Bacteroidetes.At the genus taxonomic level,Muribaculaceae,Lactobacillus,Helicobacter,Dubosiella,Lachnospiraceae NK4A136 group and Bacteroides,etc.And it has higher relative abundance in each treatment group.Fermented products of L.edodes can increase the relative abundance of beneficial microorganisms,such as Muribaculaceae,Lactobacillus,Lachnospiraceae NK4A136 group,Akkermansia,etc.In the intestinal tract to varying degrees,and reduce the relative abundance of Helicobacter,Mycoplasma,Mucispirillum,and Alloprevotella,etc pathogenic bacteria relative content.The research results show that LAB fermented L.edodes products can regulate the intestinal flora of mice to a certain extent,increase the colonization of beneficial bacteria in the intestine,and reduce the content of harmful bacteria.This provides a theoretical basis for the development of LAB fermented L.edodes functional food. |
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