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A glycoprotein α‐amylase inhibitor (α‐AI) was extracted and purified from white kidney beans (Phaseolus vulgaris. L) by ethanol fractional precipitation, ion exchange chromatography and gel filtration column chromatography. The homogeneity of α‐AI was demonstrated by gel filtration on sepharose CL‐6B and SDS‐polyacrylamide gel electrophoresis (SDS‐PAGE). The molecular weight was estimated to be about 36,000 Da by SDS‐PAGE. The glycoprotein α‐AI contained 88.2% protein and was rich in aspartic acid, glutamic acid, leucine, threonine and serine, with a trace amount of cysteine. The carbohydrate moiety, determined by reversed‐phase high‐performance liquid chromatography (RP‐HPLC), consisted of Man, Glc, Gal and Xyl in a mole ratio of 2.42:1.50:1.52:1.00. The glycan and the core protein backbone was connected by O‐linkage as determined by β‐elimination reaction. PRACTICAL APPLICATION The α‐amylase inhibitors are important because of their potential effects of insect control and crop plant defense against pests. The selective inhibition of human α‐amylase also plays an important role in reducing digestive‐starch degradation in patients suffering from diabetes and has high value in controlling human weight. In this paper, an α‐amylase inhibitor that effectively inhibits porcine pancreatic and salivary amylases was isolated and purified from white kidney bean. Therefore, it may have high potential pharmaceutical value as a regulative agent in reducing digestive‐starch degradation in patients suffering from diabetes and obesity.

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Summary The aim of the study is to compare the effect of boiling and high pressure steaming (HPS) on the degradation, inhibitory activity reduction and gastric digestibility of soybean trypsin inhibitor (STI). Thermal stability analysis showed that HPS treatment was effective in eliminating the inhibitory activity of STI than boiling. SDS‐PAGE and Western blot analysis indicated that boiling has less impact on the gastric digestibility of STI than HPS. More importantly, boiling‐pretreated STI revealed high inhibitory activity against trypsin even after digestion by pepsin in simulated gastric fluid (SGF), while HPS treatment was more effective. SDS‐PAGE analysis further verified that after boiling, STI still revealed strong binding ability to trypsin, while STI could be completely degraded by trypsin after HPS treatment for 30 min.

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