Structural Characteristics Of Dietary Fiber In Pu ’er Tea And Its Mechanism Of Improving Constipation

Tea is one of the three major beverages in the world.With the rapid development of tea deep processing industry,high value utilization of tea residue has become an important research direction.In this study,tea dietary fiber(TDF)was prepared from Pu’er tea residue.By analyzing the structure,physicochemical properties,in vitro digestion characteristics and improvement of constipation in mice,the mechanism of TDF laxative effect was further clarified from the perspective of intestinal microecology.The results provide a theoretical basis for the high value utilization of Pu’er tea residue.In the specific implementation of the study,the optimal extraction process of TDF was determined by single factor and response surface test as follows: alkali concentration at3.35%,alkaline digestion at 100°C for 2.36 h,with the material-liquid ratio at 1:27.85.The dietary fiber content of TDF after extraction was 82.26 %,with cellulose,hemicellulose,lignin and pectin at 52.10%,14.20%,15.30% and 5.00%,respectively,theabrownin content was 9.77 %.By further removing theabrownin,high purity tea dietary fiber(HTDF)was achieved,with the dietary fiber content up to 86.89%,including cellulose of 56.40%,hemicellulose of 19.60%,lignin of 18.20% and pectin of 2.13%,and the theabrownin content down to 0.94%.The monosaccharide composition of TDF and HTDF was analyzed and compared,it was found that xylose and glucose were the main monosaccharides of both,with xylose and glucose in TDF at 63.35% and 15.65%,compared to those in HTDF at 64.58% and 15.94%,respectively.X-ray diffraction analysis showed that both TDF and HTDF were cellulose type I structure,and scanning electron microscopy results showed that HTDF had fluffier and denser micropores.UV spectral analysis revealed that both TDF and HTDF had absorption peaks at 256 nm and 294 nm,indicating that p-hydroxyphenyl structural units and guaiacyl structural units were contained.Infrared spectroscopy analysis detected fewer organic functional groups such as methylene,C=O,COO-,phenol,and C-O-C in HTDF vs.TDF.Analysis of the pyrolysis products revealed that more phenolic and acid pyrolysis products were detected in TDF than HTDF.NMR analysis revealed that HTDF showed a C4 signal peak at 88.83 ppm compared to TDF.Molecular docking simulations showed that dietary fibers and theabrownin in TDF bound strongly,presumably forming 5 conventional hydrogen bonds.Further studies on the physicochemical properties and in vitro digestive characteristics of TDF and HTDF revealed that both exhibited excellent water-holding capacity,swelling power and oil-holding capacity,with the highest water-holding capacity in the large intestine,suggesting potential benefits to the laxative function.Both TDF and HTDF had a recovery rate above 90% in such digestive sites as mouth,stomach and small intestine.While TDF had a recovery rate at 77.91% in large intestine,significantly lower than that of HTDF(p<0.05),suggesting easier digestion and utilization of TDF than that of HTDF.Analysis of the active ingredients in digestive juices revealed that the release of theabrownin,total phenols and total flavonoids,and the antioxidant activity of the digestive juices were higher for TDF than that for HTDF at all stages of digestion,indicating superior antioxidant capacity of TDF than that of HTDF.To verify their laxative potential,TDF and HTDF at different doses were analyzed in a loperamide hydrochloride-induced constipation mouse model.The results showed that both TDF and HTDF improved the physiological status of constipated mice,increased weight and amount of their feces,and enhanced ink propulsion rate and gastric emptying rate.TDF and HTDF interventions resulted in varying degrees of recovery from the damages in colonic goblet cells,crypts and epithelial cells,and a decrease in inflammatory cells.In addition,the concentrations of acetylcholine and substance P increased,and the concentration of inhibitory neurotransmitter vasoactive intestinal peptide decreased,with the effect particularly significant in the TDF high-dose group.The results of the study showed that TDF was superior to HTDF in improving physiological status,biochemical and pathological indicators in constipated mice.The effects of TDF on the intestinal flora structure and short-chain fatty acids were analyzed in constipated mice by 16 S r RNA and metabolomics techniques.It was found that at the phylum level,TDF intervention significantly increased the abundance of Bacteroidetes and decreased that of Firmicutes,and at the genus level,TDF significantly increased the abundance of Lactobacillus and norank＿f＿Muribaculaceae.The results of Pearson analysis showed that the Bacteroidetes,Lactobacillus and norank＿f＿Muribaculaceae were positively correlated with constipation-related parameters,while the Firmicutes was negatively correlated with constipation-related parameters.Comprehensive analysis showed that TDF intervention could up-regulate the abundance of beneficial intestinal bacteria and down-regulate the abundance of harmful intestinal bacteria.The beneficial bacteria fermented TDF to produce short-chain fatty acids which could induce excitatory intestinal neurotransmitter production,promote gastrointestinal peristalsis.Meanwhile,short-chain fatty acids provide energy for intestinal mucosal cells and maintain intestinal environment stability,thereby improving constipation symptoms of mice.