Relationship between Trypsin-inhibitor Activity and Water-soluble Protein and Cumulative Rainfall in Sweet Potatoes

Abstract

Abstract Variance analysis and variance components showed that total, heat-stable (HS) and heat-labile (HL) trypsin-inhibitor activity (TIA) of sweet potato [Ipomoea batatas (L.) Lam. 2n = 6x = 90] roots, expressed as units or specific units, were significantly different for monthly planting dates and cultivars. There were also significant differences among planting dates and cultivars for water-soluble (ws) protein content. Patterns of variation of total, HS, and HL TLA over 12 planting dates were similar and also similar to those of water-soluble protein content for four cultivars when TLA was expressed as units instead of specific units. When 12 values of TIA (units; total HS and HL) were plotted against water-soluble protein content, a positive correlation was found for all four cultivars. However, the positive correlation disappeared or weakened when TIA was evaluated as specific units. Stepwise removal of variables in multiple linear regression of cumulative rainfall, cumulative temperature, and TIA showed that there was a large negative correlation of the natural logarithm of TIA (units; total, HS and HL) on cumulative rainfall, suggesting that TIA may vary in response to drought of sweet potatoes.