Study On Properties Of Starch Isolated From Yam Cultivated In South China

Chinese yam(Dioscorea opposita Thunb)is one of the most important tuber crops worldwide.It produce edible starchy storage tubers,which are of cultural,economic,and nutritional importance.The composition,structure,and properties of starch tend to vary greatly among different plant sources.Such diversity in starch properties suggests different applications.In this study,physicochemical,rheological,thermodynamic and the digestive properties of starches extracted from yam were investigated and compared with other starches including tapioca,sweet potato and taro.the main research results as follows:Amylose content of yam starches varied significantly with the species in the range4.83%?28.70%,all varieties of yam starches had lower solubility index,swelling power and paste clarity than tapioca starch.The lowest freezing-thawing stability was found in the yam starches,and the highest freezing-thawing stability was observed in sweet potato starch(XSSP).The RVA results indicated that all varieties of yam starches had higher pasting temperature and lower breakdown value than those of tapioca starch.All varieties yam starches had lower tan?,and high hardness and stickiness than tapioca starch,indicating strong gel formation.The resistant starch(RS)of yam starch were significantly higher than that of other tuber starch.The microscopic appearance,molecular chain structure and crystal structure of yam starches were analyzed.The main results were as follows:Starch granules of yam all exhibited elliptic shapes with larger granule sizes ranging from 17.0 to 24.3?m than tapioca,sweet potato and taro starches.The crystal types of 9 kinds of yam starches were mainly B and C,but SFY and ASY displayed A-type X-ray diffraction pattern.The crystallinity and the ratio of 1045/1022cm^-1 of yam starch were higher than those of tapioca starch.The weight average molecular weight(Mw)of yam starches were large,all of which were more than?10⁷g/mol.The chemical composition and structural characteristics of starch were significantly correlated with the properties of starch.According to the results of principal component analysis,the comprehensive characteristics of 9 kinds of yam starch were listed as follows:MPY>ASY>GXPY>GY5>SFY>GY2>GY11>LCY>SYPY.Through cluster analysis,9 kinds of yam starch were divided into three categories:the first type(GY11,GY5,GY2,GXPY,LCY,SYPY)of yam starch were easy to gelatinize,had a high breakdown value,and were not easy to retrogradation.The second type(SFY,ASY)of yam starch were not easy to gelatinize,and were easy to grow back in the gelatinization process.The third type(MPY)of yam starch had strong gelation and was not easy to retrogradation.In order to understand deeper the application of starch isolated from a newly cultivated sweet potato cultivar(Ipomoea batatas)(cv.Xingshu),The changes of the physicochemical properties starch gels by multiple freeze-thaw cycles(FTC),as comparison with other five tuber starches,were assessed for the first time in this work.The result of syneresis showed that after the FTC,XSSP displayed ultra-strong ability of holding water.The results showed that there was a remarkable difference(p<0.05)in retrogradation degree,hardness and tan?of different tuber starch gels before and after FTC.The retrogradation degree and the?H values of XSSP starch gel remarkable(p<0.05)lower than those of other starch gels during freeze–thaw treatment,and XSSP starch gel had the highest hardness before 5 FTCs,suggesting that XSSP starch gel had high freeze–thaw stability.the degree of order XSSP starch gel increased after FTC.The structure of all starch gels changed obviously during FTC.The matrix surrounding pores of XSSP starch gels were thin and typical.The ability of XSSP starch gels resisting undesirable physical changes caused by temperature fluctuations is strong when XSSP starch gel undergone freeze-thaw treatment.And its freeze-thaw stability was better than other starch gels.This study has important reference values for application of XSSP starch in frozen foods.The present study provides information on yam starch characteristics which should serve as a useful guide for later studies on yam starch utilization in food and non-food industries.