Extraction, purification and properties of trypsin inhibitor from Thai mung bean (Vigna radiata (L.) R. Wilczek)

A trypsin inhibitor from mung bean (Vigna radiata (L.) R. Wilczek) seeds grown in Thailand was extracted and characterised. The optimal extraction medium was attained by shaking the defatted mung been seed powder in distilled water (P < 0.05). The extraction time affected the inhibitor recovery significantly (P < 0.05). The extraction time of 2 h was optimum for the recovery of the trypsin inhibitor from mung bean seeds. The trypsin inhibitor from mung bean seeds was purified by heat-treatment at 90 °C for 10 min, followed by ammonium sulphate precipitation with 30–65% saturation and gel filtration on Sephadex G-50. It was purified to 13.51-fold with a yield of 30.25%. Molecular weight distribution and inhibitory activity staining showed that the purified trypsin inhibitor had a molecular weight of 14 kDa. However, the purified inhibitor had no activity under reducing condition (βME). The purified inhibitor was heat stable up to 50 min at 90 °C. The inhibitory activity was retained over a wide pH range. NaCl, at 0–3% concentration, did not influence the inhibitory activity of the purified trypsin inhibitor from mung bean seeds.