Application of the Indicator Amino Acid Oxidation Method for the Determination of the Metabolic Availability of Lysine from Indian Sorghum Protein in Young Adult Men (P08-069-19)

Abstract

Abstract Objectives To measure the protein quality of cooked sorghum by determining the metabolic availability (MA) of lysine; the first limiting indispensable amino acid. Additionally, we aimed to assess the effect of complementation by combining lentils and sorghum in a mixed meal format. Methods In a repeated measures design, the MA of lysine in sorghum was studied using the indicator amino acid oxidation (IAAO) method with L-[1–13C] phenylalanine as the indicator at four levels of lysine: 5, 8, 12, 15 mg. kg−1. d−1 in five healthy adult men. These intakes represent 13, 21, 32 and 40%, respectively, of the lysine requirement (37 mg. kg−1. d−1) for adult men. Each subject participated in 8 experimental diets: 4 lysine intakes as L-lysine from crystalline amino acid, 3 intakes of lysine from sorghum prepared by moist cooking and 1 experiment to discern the effects of complementation with lentils. The principles of slope-ratio were applied to calculate the MA of lysine in sorghum by comparing the IAAO response to varying intakes of lysine in cooked sorghum relative to the IAAO response to free crystalline lysine in the reference protein which was modelled after egg protein. Results The MA of lysine from cooked sorghum was found to be 94%. Upon complementation with lentils, there was a decline in the oxidation of L-[1–13C] phenylalanine, reflecting an increased uptake of lysine for the synthesis of protein. Conclusions The findings demonstrate that most of the lysine in cooked sorghum, the fifth most commonly consumed cereal grain, is available for protein synthesis despite being of limiting concentration. Upon complementation with lentils, there was a decrease in oxidation which highlights the effectiveness of complementation. A combination of sorghum and lentil protein in a 2:1 ratio is a viable strategy to improve the protein quality for individuals consuming a plant-based sorghum and lentil diet. Funding Sources Supported by the Canadian Institutes for Health Research. Pfizer Consumer Healthcare (Mississauga, Ontario) donated the multivitamins. Mead Johnson Nutritionals donated the protein-free powder for experimental diets.