Chemical, In Vitro, and In Situ Evaluation of Heat-Treated Soybean Proteins

Abstract

The effect on protein degradability of roasting soybeans and soybean meal and holding them at elevated temperatures for 0, .5, 1, 1.5, 2, 2.5, and 3 h was assessed using in vitro, in situ, and chemical techniques. Ruminal in vitro degradation rates decreased with initial roasting for both soybeans and soybean meal from .165 to .065 h–1 and .155 to .092 h–1, respectively. Roasting and holding for 3 h resulted in the lowest degradation rates, .037 and .029 h–1 for soybeans and soybean meal, respectively. In situ degradation rates decreased from .174 to .090 h–1 and from .069 to .012 h–1, respectively, for soybeans and soybean meal roasted and held 3 h. There were no increases in ADIN with heat processing of soybeans. However, ADIN increased from 2.3 to 4.1% when soybean meal was roasted and held 3 h. In contrast, nutritionally available lysine decreased dramatically during holding with a loss after 3 h of 22% for soybeans and 17% far soybean meal. Roasting and holding significantly increased estimated postruminally available lysine (g/kg DM) of soybeans from 6.5 to 10.5 (0 h) and 11.2 (mean, .5 to 3 h) and of soybean meal from 7.6 to 10.5 (0 h) and 14.2 (mean, .5 to 3 h). Holding soybeans and soybean meal at an elevated temperature resulted in a more thorough and extensive heat treatment than typically is obtained in commercial processing. © 1991, American Dairy Science Association. All rights reserved.