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°C and 63–65% relative humidity [RH]) were separately stored at ambient conditions (23°C–26°C and 70–80% RH) and in a semiunderground pit (19–21°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.
Highlights
Sweetpotato roots are very important staples in many parts of the world, especially in the tropics
Sucrose was the major sugar in all the sweetpotato varieties, which fluctuated during root development, starch content at the start (10th week) was not significantly different (p > .05) from the 18th week, the end (Figure 1)
This study has shown the effect of variety on the total starch and individual sugar content of selected Ugandan sweetpotato roots and their variation during root development
Summary
The changes in carbohydrate fractions (starch and sugar contents of sweetpotato roots) during storage are attributed to the activities of endogenous amylolytic enzymes (Morrison et al 1993; Takahata et al, 1995; Walter, Purcell, & Nelson, 1975). While there is considerable documentation on the changes in sweetpotato starch and sugars during storage, it is not very clear how the different postharvest handling conditions and storage methods used in Sub-Saharan Africa impact on the changes in the carbohydrate components of the sweetpotato roots. This study presents metabolic changes in the carbohydrate components during development and resulting from typical Sub- Saharan postharvest handling and storage conditions of sweetpotato roots of selected Ugandan varieties. This work builds on an earlier study on the behavior of endogenous amylases of sweetpotato roots during development and storage
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