The objective of this research was to define the quality parameters that correlate with poultry amino acid digestibility (AAD) in a set of samples derived from commercial lots of mechanically extracted soybean meal (MESBM). A total of nine samples corresponding to an equal number of lots were selected. KOH protein solubility (KOHPS) was conducted at Dairyland Labs (Arcadia, WI) utilizing the standardized procedure by Ruiz et al. (2025) with only one modification: grinding of the sample was done with a cryomill to generate a consistent particle size. Trypsin inhibitor activity (TIA) was measured at Eurofins Labs (Des Moines, IA) utilizing the AOCS (2020) method. In vivo AAD was conducted at the Animal Science Lab at the University of IL. Data were analyzed using the GLM procedure in SAS (2023) to assess correlations between KOHPS values & digestible amino acid (DAA) coefficients as well as correlations between TIA values & DAA coefficients. The significance value for all analyses was P≤0.05. A wide range of KOHPS values (83.73, 82.71, 77.21, 76.27, 74.56, 73.44, 66.01, 63.78, 38.60%) was highly correlated (R2=0.66; r=0.81; P=0.0076) with their corresponding digestible LYS (dLYS) coefficients (0.86, 0.88, 0.85, 0.80, 0.85, 0.80, 0.80, 0.81, 0.77). The KOHPS was also significantly correlated (P≤0.05) with dASP & dGLU coefficients. In contrast with solvent extracted SBM, for MESBM there was a non-significant correlation with dARG (P≥0.05). A wide range of TIA values (12.85, 11.50, 10.50, 7.59, 16.67, 15.38, 14.40, 5.03, 3.50 TUI/mg) was observed in the 9 MESBM samples, but TIA was inversely correlated only to digestible MET (R2=0.49; r=0.70; P=0.0358). Even though Ruiz et al. (2023) reported that in vivo AAD was inversely correlated to the trypsin and chymotrypsin inhibitor contents in solvent extracted SBM, those SBMs were high in KOHPS (~80%). In the present study the three highest TIA values (16.67, 15.38, 14.40 TUI/mg) are in samples with low KOHPS values (74.56, 73.44, 66.01%, respectively) explaining why no other inverse correlations between TIA and DAA coefficients are observed. In conclusion, these data indicate that KOHPS is the predominant QC parameter in MESBM to assess its nutritional quality.

Ruiz, N., C. Parsons, B. Parsons and J. Buseman. 2026. KOH protein solubility is relevant in the manufacture of mechanically extracted soybean meal by dry extrusion. 2026 International Poultry Scientific Forum, abstract T189.