Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 3, 2012
Publication Date: N/A
Interpretive Summary: Free amino acids (i.e. not protein-bound) in fruit and vegetables serve as the building blocks for proteins and as metabolic intermediates in the synthesis of many of the molecules necessary for the plant’s well being. Present methods of amino acid extraction and quantitative analysis suffer one or more limitations. This situation is illustrated with the natural free amino acid, citrulline. Citrulline occurs in higher levels in some cucurbits, watermelon for example, and is receiving clinical attentionas a natural blood pressure regulator. A reliable method for the extraction and quantification of citrulline and its associated metabolic amino acids does not exist.
An extraction and quantification procedure was developed that allowed analysis of all free amino acids in fruit and vegetable tissues. Analysis of a number of commercially important cucurbits demonstrated that citrulline and its metabolic relatives could each be separated and quantified. With this methodology in place, scientists can develop higher citrulline-producing cultivars and optimize growing conditions favorable for increased citrulline production.
High performance liquid chromatography of dabsyl derivatives of amino acids was employed for quantification of physiological amino acids in selected fruits and vegetables. This method was found to be particularly useful because the dabsyl derivatives of glutamine and citrulline were sufficiently separated to allow quantification of each. Water extraction of ground, frozen-thawed tissues effected complete recovery of the physiological amino acids as demonstrated by spiking experiments and tissue combination experiments. Physiological amino acid levels were determined for peach, apple, potato, onion, tomato, bell pepper, broccoli, and seven types of cucurbits. Citrulline was present in all cucurbits except straight-necked yellow squash. Citrulline levels in the cucurbits ranged from 14 mmoles/kg dry weight in buffalo gourd up to 280 mmoles/kg dry weight in Botswana wild watermelon.