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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Application of the Indicator Amino Acid Oxidation Technique for the Determination of Metabolic Availability of Sulfur Amino Acids from Casein versus Soy Protein Isolate in Adult Men^1,2

³ Research Institute, Hospital for Sick Children, Toronto, ON, Canada M5G 1X8; ⁴ Department of Nutritional Sciences, University of Toronto, Toronto, ON Canada M5S 2Z9; and ⁵ Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5

^* To whom correspondence should be addressed: E-mail: paul.pencharz{at}sickkids.on.ca.

Our objective was to determine the metabolic availability (MA) of sulfur amino acids in dietary proteins using the indicator amino acid oxidation (IAAO) technique. Five to seven men received graded levels (20, 40, 60, and 70%) of the mean total sulfur amino acid (TSAA) requirement of 13 mg · kg^–1 · d^–1 as a crystalline AA mixture, casein, and soy protein isolate (SPI) (40, 50, 60, and 70%), respectively. Five of these subjects received 40% of TSAA requirement from SPI supplemented with methionine to the level of 40% of requirement. These 5 subjects also repeated the level of 60% TSAA requirements from both casein and SPI to assess repeatability. The mean MA of TSAA from SPI (71.8 ± 3.6%) was lower than from casein (87.4 ± 3.8%, P < 0.05). Supplementation of SPI with methionine decreased the IAAO (11.5 ± 0.3% administered dose) compared with unsupplemented SPI (12.8 ± 0.5% administered dose, P < 0.05). IAAO was similar for repeated measurements of casein and SPI, respectively, at the 60% TSAA intake level (10.8 ± 1.0 vs. 10.7 ± 1.2% for casein; 12.7 ± 1.3 vs. 12.9 ± 2.6% for SPI). In conclusion, the IAAO technique can be used to determine the MA of AA for protein synthesis in test proteins for humans.

This article has been cited by other articles:

				R. Elango, R. O. Ball, and P. B. Pencharz Indicator Amino Acid Oxidation: Concept and Application J. Nutr., February 1, 2008; 138(2): 243 - 246. [Abstract] [Full Text] [PDF]