Abstract
Tora bean α-amylase inhibitor (TAI) was a proteinaceous α-amylase inhibitor from Phaseolus vulgaris cultivar Tora, a common kidney bean in Japan, and it was active against pancreatic and salivary α-amylases. We investigated the behavior of this inhibitor during heat treatment and enzymatic digestion in order to evaluate the nutritional significance of kidney bean α-amylase inhibitor. The inhibition against pancreatic α-amylase increased with a rise in preincubation temperature from 25 to 45°C. TAI was relatively stable in pH 7.0 after 20min incubation at 80°C, while it was rapidly inactivated in pH 3.0 and 5.0. Soaking of tora beans in water for 15h at 20°C caused an decrease of soluble protein content, but hardly affect the inhibitory activity, while boiling treatment for 15min inactivated nearly 90% of the inhibitor. The inhibitor was quite resistant to the proteolysis by pepsin and trypsin, while it was relatively susceptible to hydrolysis by chymotrypsin and lost about 90% of the original activity during 2h digestion.
