Impact of Food Processing State on the Proximate Composition of Soybean (Glycine max) used as a Feed Ingredient

This study examined the effects of different processing methods on the proximate composition of soybean (Glycine max) for potential use as a feed ingredient. Six processing treatments were evaluated: uncooked, cooked, overcooked, extruded, extruded-dirty (extruded with impurities), and defatted. The analysis revealed significant differences (P < 0.05) in crude protein, crude fat, moisture, crude fiber and ash contents across the processing states. Extruded soybeans demonstrated superior nutritional quality, exhibiting the highest crude protein (42.52 ± 0.38%) and crude fiber (7.37 ± 0.33%) levels, along with the lowest moisture content (8.52 ± 0.29%). Conversely, soybeans subjected to overcooking recorded the lowest protein content (24.79 ± 0.30%) and the highest moisture level (40.46 ± 0.37%), indicating potential nutrient degradation from prolonged heat exposure. Defatted soybeans retained high protein (40.66 ± 0.24%) with the lowest fat content (0.51 ± 0.05%), making them ideal for low-fat feed formulations. Uncooked and cooked soybeans showed similar compositions, with uncooked soybeans having slightly higher protein (39.18 ± 0.45%) and fat (17.56 ± 0.35%) than cooked ones (38.43 ± 0.34% and 15.48 ± 0.42%, respectively), though differences were not significantly observed. These key observations strongly suggest that the extrusion process significantly enhances the nutritional quality of soybean, while excessive heat treatment reduces feed potential value of soybeans.