Influence of development, postharvest handling, and storage conditions on the carbohydrate components of sweetpotato (Ipomea batatas Lam.) roots

Abstract

Changes in total starch and reducing sugar content in five sweetpotato varieties were investigated weekly during root development and following subjection of the roots to different postharvest handling and storage conditions. Freshly harvested (noncured) roots and cured roots (spread under the sun for 4 days at 29-31 degrees C and 63-65% relative humidity [RH]) were separately stored at ambient conditions (23 degrees C-26 degrees C and 70-80% RH) and in a semiunderground pit (19-21 degrees C and 90-95% RH). Changes in pasting properties of flour from sweetpotato roots during storage were analyzed at 14-day intervals. Significant varietal differences (p<.05) in total starch, sucrose, glucose, maltose, and fructose concentrations were registered. The total starch and sucrose content of the roots did not change significantly (p<.05) during root development (72.4 and 7.4%, respectively), whereas the average concentrations of glucose, maltose, and fructose decreased markedly (0.46-0.18%, 0.55-0.28%, and 0.43-0.21%), respectively. Storage led to decrease in total starch content (73-47.7%) and increase in sucrose and glucose concentrations (8.1-11.2% and 0.22-1.57%, respectively). Storage also resulted in reduction in sweetpotato flour pasting viscosities. Curing resulted in increased sucrose and glucose concentrations (9.1-11.2% and 0.45-0.85%, respectively) and marked reduction (p<.05) in total starch content (72.9-47.6%). This resulted in low pasting viscosities compared to flour from storage of uncured roots. These findings show that significant changes occur in the carbohydrate components of sweetpotato roots during storage compared to development and present an opportunity for diverse utilization of flours from sweetpotato roots in the food industry.