Abstract
The colorimetric method assay for the trypsin inhibitor activity (TIA), using porcine pancreatic trypsin as enzyme and BAPA (Benzoyl-D, L-arginine-p-nitroanilide) as substrate was modified to become suitable for microplate analysis. Our method allows sweetpotato (Ipomoea batatas (L.) Lam) breeders to analyze rapidly a large number of samples using a smaller sample size. In the present study, this method was applied to determine the TIA of sweetpotato genotypes. The coefficient of determination (R2) of TIA with the partially purified trypsin inhibitor (SPTI) and the commercially available soybean trypsin inhibitor in a range of 0-1 μg was 0.974 and 0.999, respectively. A single microplate required approximately 30 min for sample preparation and 90 min for analysis. Sweetpotato roots of 8 cultivars and 199 breeding lines at the initial stages of a breeding program were analyzed for TIA. The TIA values of 8 cultivars ranged for 65 to 392 U/mg DW with an average value of 197 U/mg DW. On the other hand, The TIA values of the 199 lines ranged from 38 to 944 U/mg DW with an average value of 273 U/mg DW. These data revealed that TIA was considerably higher in the breeding lines than in the cultivars tested. In conclusion, the TIA range of the breeding lines was relatively wide and in some of the lines with a higher TIA value the threshold level may exceed that for pigs estimated by the conversion value of TIA to the amount of soybean trypsin inhibitor.
