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Adhesive and hydrophobic properties of alkalimodified soy protein (AMSP) and trypsin-modified soy protein (TMSP) on wood were investigated. Modifying soy protein (i) under moderate alkaline conditions (pH 10.0 at 50°C) and (ii) with trypsin, enhanced adhesive strengths (730 and 743 N, respectively) compared with unmodified soy protein (340 N). Hydrophobicities of AMSP, TMSP, and unmodified soy protein isolate by sodium dodecyl sulfate binding and 1-anilino-8-naphthatene sulfonate methods were 7.6, 6.4, 5.0 and 39, 27, 13, respectively. Modified soy protein adhesives with higher hydrophobicities (AMSP and TMSP) had enhanced water-resistance properties.alone may not yield optimal results, combination treatments of alkaline pH coupled with a moderate temperature were explored.Water resistance is an important glue property that determines adhesive bond durability (11). To improve water resistance of soy protein glue, several cross-linking agents, such as calcium salts and carbon disulfide, have been used (11). Adhesives prepared from soy meal have poor water resistance due to the presence of carbohydrates (1 t). Improved adhesive strength and water resistance have been observed in glue prepared from trypsin-modified soy protein (TMSP) (13). Since limited information is available on the adhesive and water-resistance properties of soy protein isolates (SPI) modified by combinations of alkali and heat treatments, we investigated the effects of these treatments.Preparation of modified protein: TMSP. TMSP was prepared according to the method described by Kalapathy et aL (13). A 7% solution of SPI with trypsin (E/S = 1:50, pH 8.0) was incubated at 37°C for 1 h in a shaker (180 rpm). The enzyme was inactivated by heating at 90°C for 3 min, and the product was frozen and freeze-dried~ Degree of hydrolysis. Degree of hydrolysis was determined by measuring insoluble nitrogen in 10% trichloro

Soy protein isolates (SPI) with varying degrees of hydrolysis (DH of 7, 11, 15, 17%) were produced using pancreatin. The surface hydrophobicity indices of pancreatin hydrolyzed SPI (PSPI) (34.5, 34.9, 39. 1, and 40.7 for 7, 11, 15, 17% DH, respectively) were higher than that of SPI (10.5) and control SPI (CSPI) (12.5, 11.9, 12.9, and 12.6 for 10, 60, 120, and 180 min incubation, respectively). The solubilities of PSPI at pH 4.5 were 2.7, 9.1, 11.9, and 18.7%, for 7, 11, 15, and 17% DH, respectively, while the solubilities of SPI and CSPI at the same pH were about 1. 6%. Solubilities of PSPI at pH 7. 0 were > 90% for all DHs tested, while those of SPI and CSPI were 85%. The emulsifying activity index (EAI) of PSPI increased with increasing DH. PSPI with 15% DH had highest EAI (1. 122) which was higher (P < 0. 05) than those of SPI (0.550) and CSPI after 120 min incubation without enzyme (0.568). These results suggest that PSPI could be used as an ingredient for emulsified products and where high solubility at low pH is required.

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