Trypsin inhibitor activity (TIA) and crude protein content of seven genotypes of sweet potato were investigated. There was considerable genotypic variation in TIA, with a four- to fivefold range in roots and a threefold range in stems. The mean TIA in stems at harvest time was 36% of that in roots, whilst the mean TIA in leaves was only 17% of that in roots. The TIA level in roots was correlated with that in stems (r = 0.83, p = 0.02) and leaves (r = 0.70, p = 0.08). In most genotypes the TIA level in vine-tips was low during the early growth stage, increased from day 30 to day 110 after transplanting, then remained constant in subsequent growth stages. However, in genotype Guang 70-9, vine-tips had a high level of TIA at all growth stages. Sweet potato green tissue contained three- to fivefold more crude protein than roots. No correlation between TIA and crude protein in sweet potato roots was found across genotypes, but TIA was significantly correlated with crude protein content (r = 0.73, p = 0.06) in sweet potato vine-tips. Moist heat treatment (MHT) was found to be effective in eliminating TIA in sweet potato. Most TIA in sweet potato green tissue and roots was eliminated by MHT at ≥80 °C, but heat stability was dependent on genotype. Guang 70-9 had relatively highly heat-stable trypsin inhibitor. The results suggested that screening for genotypes with high protein content and low TIA and use of an appropriate processing method could improve the utilisation of sweet potato for both human food and animal feed.
© 2001 Society of Chemical Industry