Effect of Cultivars, Cooking and Processing on the Trypsin Inhibitor Activity of Soybean

Abstract

The trypsin inhibitor activity (TIA) of various soybean cultivars was evaluated by measuring the inhibition of trypsin activity using N-benzoyl-DL-arginine-p-nitro-anilide (BAPNA) as the substrate. The TIA values of eleven white shelled soybean cultivars including a glyphosate-tolerant soybean (16.58 to 17.90 mg/g) were not significantly different among cultivars. Black shelled soybeans had higher TIA values, ranging from 40.09 to 52.11 mg/g, compared to white shelled soybeans (p＜0.05). When the TIA of commercially processed soybean foods were determined, no TIA was detected in soysauce, tofu and soybean paste. During conventional moist heating, the IT_(50) (Time required to reach 50% inhibition of TIA) values were decreased as heating temperature and cooking pressure increased. The IT_(50) values of moist heating were estimated to be 91.68, 37.71 and 19.50 min at 60, 80 and 100℃, respectively. The IT_(50) value of microwave cooking was 4.75 min at medium heat, while that of the pressure cooking at 120℃ was only 2.62 min. Moreover, there was a negative relationship between temperature and IT_(50) values (R=0.92, p＜0.01). The TIA of soybean sprouts was completely inactivated after heating at 100℃ for 5 min, although fresh soybean sprouts showed one fifth of the TIA value of white shelled soybeans. Based on our results, pressure cooking is the most effective cooking method to reduce TIA in soybeans.