REDUCTION OF β-CONGLYCININ ANTIGENICITY AND RATE OF ACID-PEPSIN PROTEOLYSIS OF PROTEINS IN EXTRUDED OR RUMEN FLUID-TREATED SOYBEAN MEAL

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Abstract
The effect of processing commercial soybean meal (HSBM) by either extrusion (ExSBM) or fermentation with microbes in rumen fluid (FSBM) on rate of protein hydrolysis and the activity of the antigen β-conglycinin was evaluated. Ethanol-extracted soybean meal (EtSBM) and skim milk powder (SMP) were included as positive controls while HSBM was the negative control, with regard to antigen content. The rates of proteolysis were determined by acid pepsin hydrolysis and the activity of β-conglycinin in the soluble fraction of the digestion mixtures at 0, 2, 4, 6 and 8 h of in vitro proteolysis was determined by radial immunodiffusion in agar gel containing antibody specific for the antigen. Susceptibility of FSBM and ExSBM to proteolysis by pepsin was greater than that of EtSBM. β-Conglycinin content was greatest in HSBM (1.0 ± 0.2 g dL−1) and only 0.3 ± 0.03 g dL−1 in ExSBM at the beginning of in vitro digestion. The antigen was not detected in either FSBM or EtSBM, therefore these products could be used in milk replacers for calves. Key words: In vitro pepsin proteolysis, extruded soybean meal, fermented soybean meal, antigen, β-conglycinin