Chemical composition, protein quality indicators and in vitro protein digestibility of commercial soybean meals from different origins for use in poultry feeding

Abstract

The chemical composition, protein quality and in vitro digestibility coefficient of the protein fraction (IVDP) of soybean meals (SBM) were studied in commercial samples from Argentina (ARG), Brazil (BRA), United States of America (USA) and South Africa (SAF) in equal numbers (n = 40). The BRA meals had more crude protein (CP; 469, 459, 462 and 462 g/kg; P < 0.001) and crude fiber (46.3, 37.5, 41.8 and 41.8 g/kg; P < 0.001) than the SAF, ARG and USA meals. Sucrose (87.6, 73.3 vs. 68.6 and 58.0 g/kg; P < 0.001) and stachyose contents (48.3, 50.8 vs. 46.7 and 44.5 g/kg; P < 0.001) were higher for the SAF and USA meals than for the ARG and BRA meals. The amino acid profile (g/100 g CP) varied with the origin of the SBM, with Lys being more abundant in the SAF and USA meals than in the ARG and BRA meals (P < 0.001). Protein quality indicators [urease activity (UA), protein dispersibility index (PDI), KOH solubility (KOH) and trypsin inhibitor activity (TIA)] values were highest for the SAF meals and lowest for the ARG meals, with USA and BRA meals showing intermediate values. At 1 and 3 h post-incubation, IVDP were higher (P < 0.001) for the USA (0.779 and 0.823) and the SAF (0.773 and 0.825) meals than for the ARG (0.759 and 0.810) and the BRA (0.760 and 0.810) meals. Independent of the origin of the SBM, significant correlations were detected between IVDP at 3 h post-incubation and TIA (r = 0.353; P < 0.001) and KOH (r = 0.217; P < 0.05), but not with UA or PDI. In conclusion, the chemical composition, protein quality and IVDP of the SBM varied with the origin of the beans. Consequently, nutritionists and feed mill managers should use different matrices to evaluate more accurately the nutritional value and protein quality of SBM of different origin.