Objective: The present work was conducted to evaluate suitable variables and develop prediction equations using chemical composition and physical characteristics for estimating standardized ileal digestibility (SID) of lysine (Lys) in full-fat soybeans (FFSB).
Methods: The chemical composition and physical characteristics were determined including trypsin inhibitor activity (TIA), urease activity (UA), protein solubility in 0.2% potassium hydroxide (KOH), protein dispersibility index (PDI), lysine to crude protein ratio (Lys:CP), reactive Lys:CP ratio, neutral detergent fiber (NDF), neutral detergent insoluble nitrogen (NDIN), acid detergent insoluble nitrogen (ADIN), acid detergent fiber (ADF), L* (lightness) and a* (redness). Pearson's correlation (r) was computed, and the relationship between variables was determined by linear or quadratic regression. Stepwise multiple regression was performed to develop prediction equations for SID of Lys.
Results: Negative correlations (p<0.01) between SID of Lys and protein quality indicators were observed for TIA (r=-0.80), PDI (r=-0.80) and urease (r=-0.76). The SID of Lys also showed a quadratic response (p<0.01) to UA, NDIN, TIA, L*, KOH, a* and Lys:CP. The best-fit model included TIA, UA, NDIN and ADIN, resulting in the highest coefficient of determination (R2=0.94).
Conclusion: Quadratic regression with one variable indicated the high accuracy for UA, NDIN, TIA and PDI. The multiple linear regression including TIA, UA, NDIN and ADIN is an alternative model used to predict SID of Lys in FFSB to improve the accuracy. Therefore, multiple indicators are warranted to assess either insufficient or excessive heat treatment accurately, which can be employed by the feed industry as measures for quality control purposes to predict SID of Lys in FFSB.
Keywords: Digestibility; Heat Indicator; Lysine; Prediction; Soybean.