Physicochemical properties and amylopectin structure of Yam starch (Dioscorea hispida Dennst.) and lasseryam starch(Dioscorea esculenta (Lour.) Burkill)

Abstract

Chemical composition, granule morphology, physicochemical properties (paste viscosity, thermal properties, swelling and solubility) and amylopectin structure of starches isolated from yam (Dioscorea hispida Dennst.; kloy in Thai) and lasseryam [Dioscorea esculenta (Lour.) Burkill; manmuesau in Thai] were investigated. Granules of both starches had similar size (1-6 µm) and shape (polygonal with smooth surface). Their amylose contents were comparable at 20 and 19%, respectively. Gelatinization temperature, paste viscosity, breakdown and setback of yam starch were 80.3°C, 157.3, 8.8, 25.3 RVU, whereas those of lesseryam starch were 77.1°C, 248.0, 67.8, 47.5 RVU, respectively. Lesseryam displayed 10 to 15% higher swelling power as compared to yam starch. Amylose leaching of lesseryam and yam starches was initially observed at 70°C and 80°C, respectively. Analyses of amylopectin structure revealed that weight based ratios of short chain (A+B1) to long chain (B2+B3+B4) of yam and lesseryam starches were 1.3 : 1 and 1.9 : 1, while molar based ratios were 5.7 : 1 and 8.8 : 1, respectively. Average chain length of amylopectin was 15.8 for yam starch and 13.5 for lasseryam starch.