Effect of Different Storage Conditions on Biophysical and Nutritional Properties of Sweetpotato Storage Roots in Uganda

Abstract

Most recent studies on sweetpotato storage in Africa have compared the effect of different storage facilities such as storage bags and traditional and modified pits on the quality of sweetpotato. There are limited recent studies on the effect of storage conditions with regards to different temperature and humidity conditions on biophysical and nutritional composition of sweetpotato storage roots by variety. The objective of the study was to characterize shelf stability of sweetpotato storage roots and compare the biophysical and nutritional changes among six sweetpotato genotypes stored in three temperature-humidity conditions. Sweetpotato storage roots of six released varieties of varying flesh colors (Ejumula, SPK004, NASPOT 8, NASPOT 10 O, NASPOT 13 O, and Tanzania) were harvested from farmers’ fields in Serere. They were stored under three different storage conditions: cold (8-10°C), warm (30°C, >90% humidity), and room conditions without heaping. Three roots of each variety were retrieved at baseline, day 1, day 4, day 7 and day 14 of the experiment. These roots were freeze-dried to evaluate dry matter content. The freeze-dried powders were scanned with NIRS to analyse their starch, sugar (glucose, fructose, sucrose) and betacarotene contents. The powder was packaged in airtight plastic bags and transported to FANEL in Kenya where it was analysed for sugar, vitamin C and betacarotene content using HPLC. The data were analysed using ANOVA with repeated measures. Roots of NASPOT 8 started spoiling or rotting during storage under all three conditions, and most varieties started sprouting in warm conditions. There was no significant loss in dry matter of the samples until the last day. Starch content decreased while sucrose content of the roots increased over the storage period. The highest increase in sucrose was observed in roots stored under cold conditions, with the highest increase observed in roots of Tanzania. The roots were generally low in vitamin C. Storage and variety had mixed effects on betacarotene content. The study demonstrated that sweetpotato roots of some varieties can be stored under room conditions for longer than one week, albeit some nutritional loss trade-offs. The sensory and safety effects of these storage conditions should be studied, especially among varieties that keep for long in room conditions to develop storage practice recommendations and build suitable infrastructures.