Cultivar Differences in Trypsin Inhibitors of Sweet Potato Roots

Abstract Cultivar differences in the heat deactivation temperature of trypsin inhibitors in an extract of chopped tissue were examined. In addition, the distribution of trypsin inhibitor activity in the root and existence of different trypsin inhibitor proteins within and among 4 cultivars were investigated. There was a significant cultivar-by-temperature interaction during the heat deactivation test. Activity in ‘Jewel’ was decreased by 50% at a significantly lower temperature (65°C) than the other cultivars (75°) indicating that ‘Jewel’ contains more heat labile trypsin inhibitors. The longitudinal distribution of trypsin inhibitor activity was dependent on the cultivar. All cultivars had increased levels of trypsin inhibitor activity in the proximal or stem end. Sectioning of roots, in order to eliminate high trypsin inhibitor activity, would not be reliable since there is a cultivar-by-section interaction, and the gradients are not large enough to eliminate the majority of trypsin inhibitor activity by removal of one section. The cross-sectional gradient of trypsin inhibitor activity in the roots also depended on the cultivar. There was a high level of trypsin inhibitor activity in the cortical region of all cultivars. The concentration (over 50%) of trypsin inhibitor activity in the cortical area of the root in ‘Jewel’ and ‘Caromex’ could be important when heat deactivating the whole root. Disc-gel electrophoresis revealed that the trypsin inhibitor fraction isolated via affinity chromatography was heterogenous. There were 7 different trypsin inhibitor bands after electrophoresis at pH 8.9 in 7.5% acrylamide gels. The quantitative distribution of these seven trypsin inhibitor proteins differed among cultivars. These different distributions may be responsible for the cultivar differences previously observed.