A new method to simultaneously analyze the contents of various free amino acids related to flavor and umami taste (alliin, methiin, aspartic acid, and glutamic acid) in Allium tuberosum was established in the present study. This method was employed to investigate variations in these amino acids during growth in summer. The moisture, nutrient, and polyphenol levels as well as antioxidant capacity of A. tuberosum were also examined. The contents of the four amino acids per fresh weight increased with the growth of A. tuberosum. Aspartic acid and glutamic acid contents positively correlated with those of alliin and methiin. The correlations observed among amino acid contents were attributed to the synthesis of methiin and alliin increasing concurrently with the activation of amino acid synthesis with growth. Moreover, the contents of the four amino acids negatively correlated with that of water and positively correlated with those of carbohydrates and calcium. However, their contents did not correlate with that of polyphenols or the antioxidant capacity. In contrast, the content of water in the leaves decreased with the accumulation of nutrients.
