Extraction Of Tea Polysaccharides And Effect On Retrogradation Of Wheat Starch

The extraction of tea polysaccharides from green tea grown in Zhejiang province was investigated,as well as their effects on the retrogradation of wheat starch by differential scanning calorimeter (DSC),viscosity meter(RVA), fourier infrared (FTIR), texture profile analysis (TPA) and scanning electronmicroscope(SEM). The results could provide a new method for improvement of wheat starch quality aswell as enlarge the utilization of tea resources.Green tea grown in Zhejiang province was used as raw material.Extraction of tea polysaccharideswas optimized by response surface method on the base of single factor test. Extractiontemperature,extraction time, the ratio of solid to liquid was chosen as test factors. The results were analyzedbyDesign Expert8.05software. It was shown that the optimimun extraction conditions were extractiontemperature82℃, the ratio of solid to liquid33:1, extraction time106min, meanwhile the yield of teapolysaccharides3.44%was obtained. Thereafter three parallel verification experiments were conducted,and the yield of tea polysaccharides was3.22%、3.36and3.45%, in average3.41%. The difference ofverification result to theoretical result was0.03%.Furthermore, effect of tea polysaccharides on retrogradation of wheat starch was investigated bythe instrumental analysis. DSC results showed that the retrogradation ratio of wheat starch decreased asincrease of tea polysaccharide ratio when ratio when wheat starch was stored at4℃for3d,7d and14d,respectively. It was found by RVA analysis that the setback of wheat starch decreased by30cP and33cP,respectively, when the concentration of tea polysaccharide was4%and8%. FTIR showed that the(1045/1022) cm-1peak intensity ratio of original wheat starch was1.32,1.94times as that of wheatstarch adding2%,4%tea polysaccharides stored for7d. TPA showed that as the tea polysaccharidescontent increasing, the hardness, adhesiveness, chewiness of wheat starch paste gradually decreased. Itwas observed by SEM that the size of starch granules decreased as content increase in teapolysaccharides.Taking sample of wheat starch with2%tea polysaccharides as example, cancellousshape appeared at storage for3d. In general, the above results showed that tea polysaccharides couldretard the wheat starch retrogradation.