Glutamine in Commercial Liquid Nutritional Products

• Published in: Journal of agricultural and food chemistry 2004-08, Vol.52 (16), p.4963-4968
• Main Authors: Baxter, Jeffrey H, Phillips, Rosalyn R, Dowlati, Lobat, Johns, Paul W
• Format: Article
• Language: English
• Subjects: amino acid derivatives; Biological and medical sciences; Chromatography, High Pressure Liquid; dietary supplements; enzymatic hydrolysis; food analysis; Food industries; Food, Formulated - analysis; free amino acids; Fundamental and applied biological sciences. Psychology; glutamine; Glutamine - analysis; high performance liquid chromatography; Hydrolysis; leucyl aminopeptidase; Milk Proteins - analysis; proteinases; pyroglutamic acid; Reproducibility of Results; Research and development. New food products, dietetic foods and beverages; Solutions
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf049627h

Total glutamine concentrations in commercial nutritional products have been determined by enzymatic hydrolysis followed by HPLC quantification of free glutamine and free pyroglutamic acid. Hydrolysis was accomplished by a published three-enzyme (Pronase, leucine aminopeptidase, prolidase), 20-h/37 °C digestion. Glutamine was determined as its FMOC derivative by reverse phase HPLC-fluorescence, and pyroglutamic acid was determined directly by organic acid HPLC-UV. Approximately 4.11% of the released glutamine is converted to pyroglutamic acid during the 20-h digestion. Experimental ratios of enzyme hydrolysis glutamine to acid hydrolysis glutamic acid + glutamine + pyroglutamic acid (GLX) indicate that the method recovers >90% of the protein-bound glutamine. The nutritional products with casein dominant intact protein systems typically deliver >9 g of glutamine/100 g of protein, or ∼40 g of glutamine/100 g of GLX. Keywords: Glutamine; pyroglutamic acid; enzyme hydrolysis; nutritional products; HPLC