Precise nutrition 1: Standardization of the KOH protein solubility test for soybean meal in a single commercial laboratory and correlation to in vivo poultry amino acid digestibility

The KOH protein solubility ( KOHPS ) method to evaluate if a lot of commercial soybean meal ( SBM ) has undergone the Maillard reaction during processing was introduced to the animal feed industry by Araba and Dale (1990). Although it is used worldwide, there are 2 limitations that have not been addressed. There is large inter-laboratory variability of the test and an absence of a quantitative interpretation of the results in terms of amino acid ( AA ) digestibility that can be used by nutritionists and formulators for commercial SBM affected by the Maillard reaction. The objective of this study was to standardize the KOHPS method in a single commercial laboratory starting from the description by Araba and Dale (1990) by using commercial SBM samples whose in vivo AA digestibility status was known. For this purpose, 2 SBM samples, one with high solubility (80 to 85% KOHPS) and another with low solubility (KOHPS ∼ 50%), were used as reference samples to develop a preliminary protocol. Then adjustments in intensity of agitation were made with 4 SBM samples of known in vivo digestible Lys coefficients (0.88 to 0.96) to yield KOHPS values from 80% to 85%. The standardized protocol yielded KOHPS values from 50 to 56% for the low solubility SBM reference sample and 3 samples known to have low in vivo digestible Lys coefficients (0.73 to 0.77). In conclusion, a standardized protocol is now available for the determination of KOHPS of commercial SBM that will allow regression equations to be developed for the estimation of digestible AA.