Protein degradability, amino acid composition, trypsin inhibitor and urease activity of raw and heat-treated fullfat soybean.

The effects of different heat treatments were studied on chemical composition, protein degradability, amino acid composition, trypsin inhibition and urease activity. Three lactating Holstein cows fitted with rumen cannulae were used. Fullfat soybean was prepared employing different forms of heat treatment: dry-extrusion at 150 degrees C for 25 s (treatment I); wet-extrusion at 95 degrees C for 30 min (treatment II); toasted soybean at 105 degrees C for 30 min (treatment III) extracted soybean meal (treatment IV); and untreated soybean (treatment V). The incubation times were 0, 2, 4, 8, 16, 24 and 48 h. Samples of raw and heat-treated soybean before incubation and the undegraded fraction after 4 and 16 h of incubation were analyzed for amino acids. The results showed that heat treatments did not modify chemical composition, but significantly reduced the content of trypsin inhibition and urease activity, as well as decreased protein degradability. The dry extrusion technique was comparatively the most effective. Amino acid content was not significantly influenced by different techniques, but the quantity of amino acids escaping degradation in the rumen increased.