No abstract

Ground soybeans and corn at ratios 60:40, 70:30, 80:20, and 100:0 soybean :corn were extruded with an Insta Pro 600 extruder. Initial moisture content was adjusted to 10%. Extruder exit temperatures were 127, 138, 149, and 160°C. Soybean trypsin inhibitor activity was destroyed 48.9 to 98.8% as exit temperature increased. Extrusion temperature had no major effect on the tocopherol isomers. Lipoxygenase was completely inactivated by extrusion. In vitro protein digestibilities of samples extruded at 127°C were significantly lower than samples extruded at higher temperatures. Residual lipase activity ranged from 2.7 to 63.7 micromoles H+.min_I.g−1.

Tocopherols from soybean seeds and soybean curd (tofu) were extracted, separated and quantitated by high-performance bonded normal-phase liquid chromatography with ultraviolet (UV) detection at 280 nm. Two successive extractions with ethanol at a solvent to dry matter ratio of about 20:1 were performed. Saponification was not necessary. The tocopherols were separated in 18 min in an amino column by using 1% isopropyl alcohol in hexane as the mobile phase. Tocopherol content varied significantly from one soybean variety to another. The amounts of a-, y-, and ô-tocopherols in the soybeans ranged from 10.9 to 28.4, 150 to 191, and 24.6 to 72.5 yg/g (dry basis), respectively. Processing of soybeans into tofu results in a loss of vitamin E (47% and 30% for two varieties analyzed), but the tofu is a greater source of tocopherols than the soybeans on a dry basis. Storage of the curds for 15 days under commercial conditions does not affect vitamin E content.