| Lithocarpus litseifolius is a kind of natural tea with a history of more than 1,500years.It is known as sweet tea because of its sweet taste after brewing,and also known as the"Cordyceps sinensis in the tree"which is a combination of tea,sugar and medicine.It has the functions of lowering blood glucose,blood pressure,lipid,antioxidant,antibacterial,anti-inflammatory,inhibiting cancer cells and anti-tumor,especially its hypoglycemic effect has been widely recognized.However,the research of Lithocarpus litseifolius mainly focuses on the content of dihydrochalcone,and the other components of Lithocarpus litseifolius such as polysaccharide and its hypoglycemic function are not further studied.Polysaccharide is a kind of biological macromolecule with various structures commonly found in nature.Because of its diverse structure,unique biocompatibility,biodegradability and various pharmacological effects,it has become a hot topic of research in China and abroad.The purpose of this study was to investigate the effects of monascus solid fermentation on physicochemical properties,antioxidant and hypoglycemic function of Lithocarpus litseifolius polysaccharide,and the feasibility of preparing an effervescent tablet with fermented polysaccharide.（1）A water-soluble polysaccharide was extracted and purified from the leaves of Lithocarpus litseifolius by water extraction and alcohol precipitation combined with sevage deproteinization.Then,its structure was characterized and its antioxidant,hypoglycemic activities were evaluated.The results showed that the extraction rate of polysaccharides was 5.95±0.28%,total sugar content was 63.48±0.36%,uronic acid content was 51.64±0.34%,protein content was 3.80±0.15%,and total phenol content was 4.99±0.08%.It is a kind of acid heteropolysaccharide,consisting of galacturonic acid,rhamnose,galactose and glucose in order of mass percentage.Fourier infrared spectroscopy showed that the polysaccharide of Lithocarpus litseifolius had the characteristic absorption peak of polysaccharide and was a polysaccharide with pyranose ring structure.At the same time,the scanning electron microscope showed that the polysaccharide was irregular and flaky with smooth surface.The ABTS and DPPH free radical scavenging data and total reducing power experiments showed that the natural polysaccharides of Lithocarpus litseifolius had better antioxidant capacity.According toα-amylase andα-glucosidase activity inhibition experiments,the hypoglycemic ability of natural Lithocarpus litseifolius polysaccharide was better with the increase of polysaccharide concentration.（2）In order to investigate the effects of monascus fermentation on the structure,antioxidant activity and hypoglycemic activity of Lithocarpus litseifolius polysaccharides from Lithocarpus litseifolius leaves,which were extracted by water extraction,alcohol precipitation and deproteinized in sevage.The results showed that the extraction rate,total sugar content,uronic acid content,protein content and total phenol content were 7.21±0.18%,77.54±0.24%,54.97±0.47%,5.90±0.12%and6.12±0.30%respectively.Monascus fermentation increased the extraction rate of polysaccharides,the contents of total sugar,uronic acid,protein and total phenol.Fourier infrared spectrum showed that the absorption peak of fermented Lithocarpus litseifolius polysaccharides at 1620 cm-1was significantly stronger than that of natural Lithocarpus litseifolius polysaccharides,indicating that the content of uronic acid in natural Lithocarpus litseifolius polysaccharides was increased after fermentation.The ion chromatographic results showed that the main monosaccharides were not changed,but the mass percentage was changed in the order of galactose,galacturonic acid,glucose and rhamnose.Scanning electron microscopy（SEM）showed that the micromorphology of polysaccharides was obviously changed after fermentation,and the overall morphology was thin with holes,and the surface had smooth protrusion with different shapes.The results indicated that monascus fermentation changed the structure and composition of polysaccharides from Lithocarpus litseifolius.Through total reducing power,DPPH radical scavenging and ABTS radical scavenging experiments,it was found that the total reducing power,DPPH radical scavenging and ABTS radical scavenging rates of fermented Lithocarpus litseifolius polysaccharides were higher than those of natural Lithocarpus litseifolius polysaccharides,indicating that monascus fermentation improved the antioxidant activity of Lithocarpus litseifolius polysaccharides.The results ofα-amylase andα-glucosidase activity inhibition experiments showed that the inhibitory rate ofα-amylase andα-glucosidase activity of fermented Lithocarpus litseifolius polysaccharides was higher than natural Lithocarpus litseifolius polysaccharides,indicating that monascus fermentation improved the hypoglycemic ability of Lithocarpus litseifolius polysaccharides.（3）The fermented Lithocarpus litseifolius polysaccharide was added to effervescent tablets to prepare a fermented Lithocarpus litseifolius polysaccharide effervescent tablets.Through single factor experiment,the optimum formula of fermented Lithocarpus litseifolius polysaccharides effervescent tablets was determined as the ratio of sodium bicarbonate to citric acid 3/5,disintegrant content60%,sweetness content 3%.At this time,the effervescent piece bubbles out of the sparkling water visual effect is good,sweet and sour taste,rich bubbles,suitable for drinking.According to the quality test,the average weight difference of the efferveting tablets was less than 5%,the disintegration time was less than 5 min,the average p H was 3.948±0.30,the hardness was more than 40 N,and the maximum weight loss ratio of brittleness was 0.79%.All the indexes were in line with the requirements of Chinese Pharmacopoeia,and the finished products were beautiful.In conclusion,the main monosaccharides of natural and fermented Lithocarpus litseifolius polysaccharides were galacturonic acid,rhamnose,galactose and glucose,all with antioxidant and hypoglycaemic activities.Compared with natural Lithocarpus litseifolius polysaccharides,the extraction rate of fermented Lithocarpus litseifolius polysaccharides obtained by fermentation with monascus increased and enhanced their antioxidant and hypoglycaemic activities,probably because the solid-state fermentation with monascus increased the content of glucuronic acid,protein and total phenols in Lithocarpus litseifolius polysaccharides.Meanwhile,the effervescent tablets made from fermented Lithocarpus litseifolius polysaccharides had a sweet taste and better flavour,which met the requirements of the Chinese Pharmacopoeia.Thus,the fermentation by monascus significantly enhanced the biological activity of natural Lithocarpus litseifolius polysaccharides and laid the theoretical foundation for the high value application of Lithocarpus litseifolius in antioxidant and hypoglycaemic applications. |
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