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.
Keywords
Yam Starch; Physicochemical property; Amylopectin; Structure
