Rapid Assessment of Compositional Stability in Improved Sweet Potato Varieties: Relevance in Breeding and Utilization

Abstract

Compositional changes that occur in sweet potato after harvest can lead to inconsistencies in processed products. A better understanding of factors influencing these postharvest changes is necessary to enhance marketing, processing and utilization. This study applied a rapid and ecologically-friendly approach in investigating the influence of maturity and short-term storage on the stability of starch, protein and soluble sugar contents in six improved sweet potato varieties. Fresh roots harvested at 3.5, 4 and 5 months after planting were prepared into flour at harvest time and also after three weeks' storage under tropical ambient conditions. Composition was studied using Near Infra-red Reflectance Spectroscopy (NIRS) as a chemical-free, non-polluting, cost effective and rapid method of analysis. At harvest time protein contents ranged from 3.0% to 7.25%, starch contents 53.93% to 79.40% and total soluble sugars 3.92% to 25.02%. Protein content was significantly influenced by harvest maturity (p<0.001), but not by storage; it was generally higher at 3.5 months and reduced with increasing maturity. For starch and total soluble sugar contents the influence of maturity was significant (p<0.01 and p<0.001 respectively); the influence of storage was also significant (p<0.001 and p<0.05 respectively). In all the varieties, there were reductions in starch content during storage ranging from 1.95% - 23-73% of the total starch. Varieties with lower original starch contents were more susceptible to starch loss during storage. Soluble sugar contents increased concomitantly with the loss of starch during storage. This rapid assessment is useful in the efforts to maintain a fair level of quality control in harvested produce through appropriate varietal selection and harvest timing, and to target suitable uses for different sweet potato varieties.