Structural Features Of Polysaccharide From Gougunao Green Tea And Its Digestion And Fermentation Characteristics In Vitro

Camellia sinensis is an ancient crop that originated in the Southwest China at 60 or 70 million years ago.Tea made from its buds or young leaves has a long history of drinking.At present,tea has become an indispensable necessity in people’s daily lives with nearly half in the world drinking tea.Tea is rich in bioactive components,including tea polyphenols,amino acids,tea polysaccharides.Among them,tea polysaccharides have a wide range of biological activities,including hpyerglycemic activity,immunity regulation,and intestinal microbiota regulation.Bioactivities of tea polysaccharides are closely related to the physicochemical properties and chemical structure.However,due to its large molecular weight and complex structure features,the current research on the structure of tea polysaccharides is not in-depth.This paper took Gougunao green tea,a famous tea in Jiangxi,as raw material.First of all,the nutritional composition of Gougunao green tea was evaluated.Then,under the guidance of “the relative ordered structure of polysaccharide” theory,water-extracted tea polysaccharide was isolated and systematically purified.A total of 8 homogenous purified components were obtained and characterized.Finally,the in vitro digestion and fermentation characteristics of tea polysaccharide were explored.Main research contents and results are as follows:(1)The nutritional composition of Gougunao green tea was analyzed.The content of tea polyphenols in Gougunao green tea was 26.62%,mainly including EGCG,ECG and EGC.Total amino acids content in the Gougunao green tea was 214.63 mg/g,mainly containing aspartic acid,threonine,serine,glutamic acid,glycine,alanine,valine,leucine,phenylalanine,lysine and arginine.The water-extracted polysaccharide GPS from the Gougunao green tea was an acidic polysaccharide,mainly composed of GalA.The alkaline-extracted JGPS isolated from residue after water extraction was a neutral polysaccharide,mainly composed of Gal and Ara.(2)GPS was characterized as pectic polysaccharides.However,HPGPC profile suggested that GPS exhibited polydispersity characteristic.Due to the polydispersity and high uronic acid content,GPS was purified by a DEAE anion-exchange column and a gel permeation column.A total of eight homogeneous fractions were obtained.HPGPC profiles showed that these 8 fractions were homogeneous and could be used for subsequent fine structure analysis.From the perspective of chemical composition,GPS1 a,GPS2a,GPS3 a and GPS4 a might be RG-Ⅰ type pectin,while GPS1 b,GPS2b and GPS3 b might be HG type pectin.GPS4 b was found to be nucleic acid but not polysaccharide.Therefore,ribose should not be classified as one of the monosaccharides that constitute the tea polysaccharides.(3)The structure of three HG-type pectic polysaccharides(GPS1b,GPS2 b,GPS3b)were analyzed by different techniques such as Fourier transform infrared spectroscopy,HPAEC,methylation analysis,and 1D/2D nuclear magnetic resonance spectroscopy.The results of monosaccharide composition analysis showed that GPS1 b,GPS2b and GPS3 b were mainly composed of GalA,containing minor amounts of Gal and Ara.Methylation analysis and nuclear magnetic resonance spectroscopy showed that GPS1 b,GPS2b and GPS3 b were mainly composed of α-1,4-GalA and methyl esterified α-1,4-GalA sugar residues,which was in line with the characteristics of typical HG-type pectin polysaccharides.SEM shows that GPS1 b,GPS2b,and GPS3 b existed primarily in the form of small spherical forms.(4)The structure of four RG-Ⅰ pectin polysaccharides(GPS1a,GPS2 a,GPS3a and GPS4a)were analyzed by different techniques such as Fourier transform infrared spectroscopy,HPAEC,methylation analysis,and 1D/2D nuclear magnetic resonance spectroscopy.The results of monosaccharide composition analysis showed that GPS1 a,GPS2a,GPS3 a and GPS4 a were all mainly composed of Gal and Ara.The results of methylation analysis show that GPS1 a,GPS2a,GPS3 a and GPS4 a are mainly composed of a main chain consisting of 1,2-Rhap and 1,4-GalAp and side chains composed of arabinan and galactan,which was in line with the characteristics of typical RG-Ⅰ type pectic polysaccharides.The assignment of signals in the NMR spectra confirmed this conclusion.SEM showed that GPS1 a,GPS2a,GPS3 a,and GPS4 a existed primarily in filamentous and mesh forms.(5)In vitro digestion and fermentation characteristics of GPS were explored by in vitro digestion model and in vitro fermentation model.The results of in vitro digestion showed that GPS could reach the large intestine through the digestive tract intact without hydrolysis.The results of in vitro fermentation showed that GPS can be utilized by human intestinal flora and promote its growth.Metabolites such as short-chain fatty acids(acetic acid,propanoic acid and butyric acid)could reduce the pH of fermentation solution.Besides,GPS could regulate the composition of microbiota and exert its prebiotic activity,by inhibiting the growth of potentially harmful bacteria(EscherichiaShigella and Streptococcus)and promoting the growth of beneficial bacteria(Prevotella and Megasphaera).