Polyphenolic Compounds Of Kiwifruit Pomace Extracts And Their Effects On Intestinal Flora

Objective:In order to provide a theoretical basis for polyphenolic compounds of kiwifruit pomace as functional factors to regulate intestinal environment,we optimized the conditions for extraction of polyphenol from kiwifruit pomace and analyze their compositions.Then,the stability and antioxidant activity about kiwifruit Pomace polyphenol（KPP）in vitro digestion were investigated,at the same time,we explored the effects of KPP on intestinal microbes by huamn fecal fermentation in vitro.Methods:1.Kiwifruit pomace as raw material,based on the four factors:ultrasonic time,methanol concentration,ultrasonic temperature,ultrasonic power,the effective extraction conditions were screened by response surface methodology,then analyzed the composition of polyphenols by high performance liquid chromatography（HPLC）.2.In order to study the stability and antioxidant activity of KPP during digestion,the content of total phenolics,and flavonoids,scavenging capacity of DPPH radical and hydroxyl radical（·OH）were determined during in vitro digestion.3.The change in ammonia nitrogen（NH₃-N）and short-chain fatty acid content（SCFAs）were measured by chemical analysis and gas chromatography during in vitro huamn fecal fermentation,as well as intestinal microbes by 16S RNA.Results:1.The results of single factor showed that the extraction rate of polyphenols reached the maximum when the methanol concentration 60%,ultrasonic power at 450 W,ultrasonic temperature at 50℃and time for 20 min.The effective extraction parameters of response surface method ology were determined as 58%of methanol concentration,60℃of ultrasonic temperature,21 min of ultrasonic time,430 W of ultrasonic power.Under this conditions,the polyphenols yield reached（19.34±0.39）mg·g^-1.7 substances separated by HPLC:gallic acid,protocatechuic acid,chlorogenic acid,esculetin,catechin,epicatechin,p-coumaric acid.2.The changes of stability and antioxidant activity of the polyphenols during in vitro digestion:（1）The results showed that the polyphenols and flavonoids were relatively stable during gastric digestion,there was no significant difference compared with the blank control.After intestinal digestion,the content of them were reduced,but higher than the blank control,and the difference were statistically significant（P<0.05）.（2）The free radical scavenging scapacity of DPPH and·OH was no significant difference between the polyphenols and the blank control.And during the intestinal digestion,the two free radical scavenging rates were higher than the blank control group,and the difference were statistically significant（P<0.01）.These results are consistent with the results of polyphenols and flavonoids.3.The effects of the polyphenols on intestinal microbes:（1）Compared with the blank control group,the NH₃-N content reduced significantly after the polyphenols ferment ation with human fecal（P<0.01）,and the contents of acetic acid,propionic acid and butyric acid were reduced,the difference were statistically significant（P<0.05）.So we speculated that it may be related to changes in intestinal microbial composition in each group.（2）The intestinal microbial sequencing results show:at the level of phylum,the microorganisms in the polyphenol group are mainly Firmicutes,Bacteroidetes,Actinobacteria.On the other hand,the microorganisms in the blank group are mainly Firmicutes,Proteobacteria,and the Bacteroidetes are less.At the level of genus,the microorganisms in the polyphenol group are mainly Prevotella,Megamonas,Lactobacillus,Bifidobacterium.And the microorganisms in the blank group are mainly Megamonas,Phascolarctobacterium,Escherichia and some unclassified microorganisms.Moreover,the dominant bacterias in tpolyphenol group are Prevotella,Bacteroidetes,Lactobacillus,Bacilli.The correlation heatmap shows the negative correlation between acetic acid,propionic acid,butyric acid or NH3-N and the above dominant bacterias.Conclusion:1.The effective extraction conditions of KPP:58%of methanol concentration,60℃of ultrasonic temperature,21 min of ultrasonic time,430 W of ultrasonic power,and the extraction amount is（19.34±0.39）mg·g^-1 under this condition.2.The KPP are stable in simulated gastric digestion,and they are unstable and degraded during intestinal digestion.But compared with the blank control,intestinal digestion can increase the release of the polyphenols and enhance antioxidant activity.3.The KPP affect the composition of microorganisms and their metabolites:polyphenols can promote the proliferation of Prevotella,Bacteroides,Lactobacillus,Bifidobacterium.It indicated that the KPP can improve the intestinal environment and optimize the structure of intestinal flora,and it is expected to be exploited as a food function factor in future research.