Study On Process Optimization Of Dried Longan Fermented By Lactobacillus And Regulation Of Intestinal Flora

?Introduction?Longan is the special fruit in South China,which is rich in nutrition and occupies an important position in Guangdong agriculture.However,because of the short storage peried and production,it is hard to keep fresh.It is usually preserved after drying for long-term storage of longan.Longan is a dual-purpose fruit for food and medicine.Its polysaccharides are potential natural prebiotics,which can improve intestinal flora and shortchain fatty acid production,enhance the body's immune regulation ability.In this study,dried longan fruit was used as raw material to further optimize lactic acid bacteria fermentation technic by combining longan polysaccharides with probiotics to improve the regulating activity of the intestinal flora of longan pulp,improving its nutritional quality and texture.?Objective?Comparing the fermentation effect of longan fermented by lactic acid bacteria from different sources,screening and determining the suitable strains for longan pulp fermentation,comparing the effects of different fermentation methods on the nutritional quality of longan pulp,establishing a suitable longan pulp fermentation process.Exploring the effect of longan fermented pulp on regulating the activity of intestinal flora in mice,and clarifying the regulatory mechanism of longan fermented pulp's intestinal flora,so as to provide scientific theory and guidance for the development of longan functional healthy food.?Method?1 Screening of Lactic acid bacteria for fermented longan fruitsComparing with plant sources(Lactobacillus plantarum,Lactobacillus acidophilus,Lactobacillus rhamnosus,Lactobacillus fermentum,Leuconostoc mesenteroides)and Dairy source(Lactobacillus casei,Lactobacillus paracasei),Lactic acid bacteria inoculated into longan pulp.The effects of changes in growth rate,viable count,acidity,and flavor were selected to screen strains suitable for longan fermentation.2 Effects of different fermentation methods on the nutritional quality of dried longan fruit.Screening the best strain inoculated into dried longan pulp,using different fermentation methods including cellulase pretreatment,yeast pretrement and mixed lactic acid bacteria treatment,comparing the viable counts of lactic acid bacteria,polysaccharides and total phenols,effects of nutrient content and taste and flavor after fermentation,in order to establish the best process of lactic acid bacteria fermentation in dried longan fruits.3 Study on regulating effect of Lactobacillus fermented longan on intestinal floraLongan pulps fermented by lactic acid bacteria were treated by sterilization and non-sterilization,respectively.Considering with the recommended daily intake of 100 mL of fermented pulp for human,the mice were randomly divided into normal control group,high-dose active Lactobacillus group,low-dose active Lactobacillus group,high-dose inactive Lactobacillus group and low-dose inactive Lactobacillus group,respectively.After 14 days of intragastric administration,using ELISA method to detect S-IgA and IL-2 related immune indicators,RT-qPCR method to determine 5 kinds of intestinal microflora,and 16 sRNA method to measure microbiota diversity.?Conclusion?1 Screening of lactic acid bacteria to ferment longan fruitsSeven kinds of lactic acid bacteria can grow in the longan pulp and enter the stable phase after 12 hours fermentation.Their number of viable cells reached above 8.0 log CFU/mL.After fermentation,the total sugar content of the seven lactic acid bacteria were about 56.89 mg/mL~66.05 mg/mL,the pH of longan pulps were between 3.58~4.25,and the acidity were increased to 60.95~102.20 T°.The sensory flavor was significantly improved,and the evaluation value of the longan pulp fermented by Lactobacillus casei reached 87.3,therefore,Lactobacillus casei was selected as a fermentation strain.2 Effects of different fermentation methods on the nutritional quality of dried longan fruit.Compared with the fermentation of single lactic acid bacteria which fermented as control group,the cellulase treatment group,the yeast treatment group and the mixed lactic acid bacteria treatment group can significantly increase the number of lactic acid bacteria and the total phenol content in longan fermented pulp,and enhance the antioxidant capability of longan.After fermentation,the number of viable cells in the cellulase treatment group reached 9.35 log CFU/mL,the total phenol content was 82.2 mg GAE/100 g,the acidity was 58T°;the number of viable cells in the yeast treatment group reached 9.21 log CFU/mL,and the total phenol content was 70.8 mg GAE/100 g,the number of viable cells in the mixed lactic acid bacteria treatment group reached 8.74 log CFU/mL,each treatment group showed significant difference(p<0.05)compared with single lactic acid bacteria control group which had 8.57 log CFU/mL of viable cells count.Overall,cellulase pretreatment and fermentation methods significantly enhanced the longevity of the longan,increased the CAA value and ORAC value of the fermented pulp,and enhanced the antioxidant capacity of longan.3 Study on regulating effect of Lactobacillus fermented longan on intestinal floraThe proportion of Lactobacillus in the intestinal tract of all mice experimental group were significantly increased compared with that of control group The number of Lactobacillus in the intestine of mice after intragastric administration of longan pulp reached more than 9 log CFU/g,which was significantly higher than that of the control group(p<0.05),while the number of Lactococcus,Enterobacter,Enterococcus and Clostridium perfringens had no significant changes.It was found that active Lactobacillus had a Synergistic effect to promote Bifidobacterium to grow in intestine.The numbers of bifidobacteria of different doses of active Lactobacillus group reached 7.26 log CFU/g and 7.34 log CFU/g,respectively.The organ indexes of thymus and spleen of each experimental group were increased.The secretion of S-IgA in the intestine of high-dose fermented longan pulp mice reached more than 4?g/mL,which was significantly different from the normal control group(p<0.05).The proportion of Lactobacillus in the experimental groups were significantly increased and concentrated The results showed that the fermented longan pulp had a certain regulatory function in the intestine,and high-dose inactive lactic acid bacteria had the same functional effect of high-dose active lactic acid bacteria,which could make the stimulating effect in mice intestinal mucosal immune system.Both of them can promote thymus organ to develop and mature,this study showed that high-dose fermented longan pulp can be benefit to enhance mice immune function.