Analysis And Identification Of Flavonoids From Different Parts Of White-Flesh Guava And Their Potential Prebiotics

With the enhancement of health awareness,people’s consumption concept is more and more turning to natural food sources,among which prebiotics are the focus of attention.At present,the research on prebiotics is still limited to oligosaccharides such as oligosaccharides and oligosaccharides,and the development of new prebiotics is extremely scarce.Flavonoids are in line with the latest definition of prebiotics by ISSAP(International Scientific Association for Probiotics and Prebiotics),but there is no support from related studies.Therefore,this paper selected white-flesh guava(Pearl guava),which is rich in flavonoids,as the research object,and evaluated the components of flavonoids in the leaves,peel and flesh of white-flesh guava(WGLF,WGPF,WGFF),the prebiotic activity in vitro and in vivo,as well as the bacteriostatic effect and mechanism.It provides theoretical basis for guava flavonoids as prebiotics,and also provides experimental support for the development of new prebiotics products.1.Flavonoid composition analysis of different parts of white-flesh guavaIn this chapter,flavonoids from the leaves,peel and flesh of guava were extracted and purified,and three flavonoids extracts,namely WGLF,WGPF and WGFF,were obtained respectively.The above three flavonoids were qualitatively and quantitatively analyzed by UPLC-ESI-QTOF-MS、HPLC-ESI-MS/MS and HPLC.The results showed that quercetin glycosides were the main flavonoid extracts from the three parts of guava,but there were some differences in species and content.Quercetin pentoside and quercetin hexoside were present in WGLF and WGPF,and quercetin pentoside was the main component in both WGLF and WGPF,there contents were 56.17 0.058 μg/mg and 10.090.012 μg/mg,respectively.WGFF only contains quercetin pentoside.In addition,the components of red guava leaves flavonoids(RGLF)and white guava leaves flavonoids(WGLF)are basically the same,but the contents of each component are different.2.Prebiotics activity analysis of flavonoids in different parts of white-flesh guava in vitroIn order to study the in vitro prebiotic effect of guava flavonoids,the effects of WGLF,WGPF and WGFF on the growth curve of four probiotics(Lactobacillus acidophilus,Lactobacillus rhamnosus,Lactobacillus plantarum and Streptococcus thermophilus)were studied.WGLF with good proliferative effect was selected to calculate the prebiotic score,and the effects of WGLF on LA-5 against low p H,high bile salt and gastrointestinal environment were studied.The results showed that the growth curves of Lactobacillus acidophilus(LA-5),Lactobacillus rhamnosus(HN001),Lactobacillus plantarum(LP-115)and Streptococcus thermophilus(ST-M5)were affected by the addition of WGLF,WGPF and WGFF.Within a certain concentration range,the three flavonoids could selectively promote the proliferation of four probiotics.When the concentrations of WGLF,WGPF and WGFF were 0.156 mg/m L,0.313 mg/m L and 0.156mg/m L,respectively,the proliferation rates of LA-5 reached the highest,which were37.51% ± 1.60%,20.89% ± 0.74% and 25.46% ± 1.01%,respectively.In the calculation of prebiotic activity score,the prebiotic activity score of WGLF for LA-5,HN001,LP-115 and ST-M5 were 0.318 ± 0.051 、 0.117 ± 0.080 、 0.186 ± 0.012 and-0.270 ± 0.012,respectively.WGLF’s prebiotic activity score of LA-5 was higher than that of inulin(0.171 ± 0.015).In addition,WGLF could enhance the resistance of LA-5 to low p H,high bile salt and gastrointestinal fluid environment.3.Prebiotics activity analysis of flavonoids from leaves of white-flesh guava in vivoOn the basis of in vitro experiments,this chapter studied the effects of WGLF on the growth characteristics,intestinal flora structure and intestinal morphological structure of normal mice.The experimental results showed that the weight gain and feed utilization rate of mice after WGLF gavage were lower than those of the control group.The number of bifidobacteria and Lactobacillus in feces of mice on the 7th day after WGLF administration was higher than that of control group,while the number of E.coli and C.perfringens was lower than that of control group.The B/E value of WGLF sample group on the 7th day(1.33 ± 0.02)was higher than that of control group(1.23 ± 0.03),indicating that WGLF could improve the proportions of beneficial microflora in intestinal tract of mice.In the HE staining experiment,the height of villi in the duodenum and ileum of mice in the WGLF sample group was higher than that of the control group,while the depth of the crypts was lower than that of the control group.In WGLF group,except jejunum,the V/C ratio of duodenum and jejunum of mice was higher than that of control group.It could be seen that WGLF treatment helps to improve the intestinal morphological structure of mice and promote the absorption of nutrients in the small intestine.It was a good potential probiotic.4.Bacteriostatic effect and mechanism of flavonoids in different parts of white-flesh guavaIn this chapter,the inhibitory effects of WGLF,WGPF and WGFF on four intestinal bacteria(E.coli,S.aureus,Salmonella and Shigella)were studied,and the best inhibitory effect of WGLF on E.coli and S.aureus was selected to explore its inhibitory mechanism.The results showed that WGLF,WGPF and WGFF had good inhibitory effects on E.coli,S.aureus,Salmonella and Shigella.According to the results of MIC,MBC and time-kill assay,the inhibitory effect of three flavonoids on S.aureus was better than that of E.coli,Salmonella and Shigella.The order of inhibitory effect of three flavonoids on four bacteria was WGLF > WGPF > WGFF.However,when the sample concentration was higher,the growth of Salmonella and Shigella was inhibited,and when the sample concentration was lower,the growth of Salmonella and Shigella was promoted,and the mechanism needed to be further studied.WGLF could cause the leakage of intracellular proteins and potassium ions of E.coli and S.aureus,and had a good dose-effect relationship.The highest PI staining rates of E.coli and S.aureus treated with WGLF were 80.1% and 100% respectively.According to the analysis of scanning electron microscopy and transmission electron microscopy,WGLF could cause the morphological structure and internal tissue damage of E.coli and S.aureus,thus inhibiting the growth of pathogenic bacteria.