J. Sci. Food Agric. zyxwvutsrq 1982,33, 1327-1330 zyxwvut The Extractability of Winged Bean zyxw (Psophocarpus tetragonolobus) Seed Trypsin Inhibitors Nget-Hong Tan, Eunice S. H. Lowe and Mohd Iskandar Department of Biochemistry, University of Malaya, Kuala Lumpar, Malaysia (Manuscript received 16 March 1982) The extractability of winged bean (Psophocarpus tetragonofobus) seed trypsin inhi- bitors by aqueous salt solution varies with pH as well as the ionic strength of the extraction medium. With a high ionic strength extraction medium, the extractability of the seed trypsin inhibitors increases with rising pH. With a low ionic strength extraction medium, however, a region of minimum extractability of trypsin inhibitors was observed at pH 4. At pH above 7, the same maximum amount of trypsin inhibitors (1.47 million inhibitor units (i.u.) per 100 g of seed meal) was extracted with both high and low ionic strength extraction media. The solution characteristics of winged bean seed proteins exhibited similar trends. Ninety-five per cent of the extracted seed trypsin inhibitors could be precipitated from 30-70 zyxw % saturated ammonium sul- phate solutions. The winged bean seed trypsin inhibitors isolated by ammonium sul- phate fractionation lost all inhibitory activity when heated at 100°C for 10 min at alkaline pH. 1. Introduction Early studies on the winged bean seed indicated heat-labile anti-proteolytic activity in the aqueous extracts of the mature seeds.la2 Several trypsin inhibitors and a chymotrypsin inhibitor have sub- sequently been isolated and purified.3-6 Cerny et af. reported that winged bean seed trypsin inhibitor activity could be destroyed relatively easily by moist heat treatment. Subsequently it was reported that without presoaking it was difficult to inactivate the seed trypsin inhibitor^.^ Before studying the properties of the seed trypsin inhibitors it is necessary to examine the insolubility behaviour. This paper reports the effect of pH and ionic strength on the extractability of trypsin inhibitors and proteins from a Malaysian variety of winged bean seeds. 2. Materials and methods 2.1. Materials Winged bean (Psophocarpus tetragonofobus) seeds of the Malaysian variety were purchased from Pusat Pengeluaran Tanaman, Ministry of Agriculture, Serdang, Selangor, Malaysia. The seeds were ground manually with a pestle and mortar and the powder was stored below 0°C in a glass container before use. Bovine trypsin and zyxwv N-benzoyl-m-arginine-p-nitroanilide (BAPNA) were purchased from Sigma Chemicals. p-Nitrophenyl-p’-guanidinobenzoate HCI was from Merck. All other chemicals are of analytical reagent grade. 2.1 Extraction of winged bean seed trypsin inhibitors Finely ground winged bean seed meal (500 mg) was extracted with 10 ml of extraction medium (containing zyxwvuts 10% sodium chloride for high ionic strength extraction and 0.1 M sodium chloride for low ionic strength extraction) for 5 h with gentle shaking. After the first hour, the pH of the 0022-5142/82/1200-1327 $02.00 zyxwv 0 Society of Chemical Industry 1321