Predicting integrated protein nutritional quality Part 1: Amino acid availability corrected amino acid score and nitrogen balance data fitted to linear and non-linear models for test proteins

As part of research to establish a mathematical relationship between overal l protein quality and in vivo protein digestibility/amino acid availability , proteins anticipated to have widely differing nutritional qualities were compared by estimating true ileal protein digestibility (TD) and essential amino acid availability (AAA) in crossbred barrows implanted with T-cannula s at the ileocecal junction, and nitrogen balance vs. nitrogen intake in si milar, non-cannulated barrows. The nitrogen intake-response data were fitte d to both linear and nonlinear models to evaluate protein quality. TD range d from 56% for whole sorghum to 100% for casein. Essential amino acid avail ability was low and variable for whole sorghum grain (30-73%) and higher an d more consistent for decorticated extruded sorghum, cowpea, and sorghum/co wpea blend (80-90%). Human and Swine Amino Acid Availability-Corrected Amin o Acid Scores (AAACAAS) ranged from similar to 0.08 (lysine) for whole sorg hum in swine to similar to 0.92 (threonine) for casein projected in humans. Linear slopes indicated relative quality to be: casein (0.70) > extruded c owpea/sorghum blend (0.55), extruded cowpea (0.52) > extruded sorghum (0.41 ) > whole ground sorghum (0.31). The saturation kinetics model predicted K- 0.5 (nitrogen intake required for half-maximal response) values of 14.8 g/d ay for casein, 20.8 for cowpea, 20.2 for sorghum/cowpea blend, 34.1 for who le sorghum, and 40.6 for extruded sorghum (C) 1999 Elsevier Science Inc.