Varying Levels of Sugars, Acids, Amino Acids, and Monoterpenes contained in Muscat of Alexandria Grapes Produced in Okayama

Sugars,acids, amino acids, and monoterpenes in Muscat of Alexandria grapes were analyzed to elucidate the distribution of the fruit taste and aroma. Fruit bunches were collected from 25 commercial vineyards in Okayama Prefecture, comprising six early heated, nine normally heated, and 10 unheated greenhouses, at mid-harvesting time in each vineyard. Juice was squeezed out by head and used for analyses. Total soluble solids (TSS) content in juice from 3 vineyards were lower than 16°Brix, the lowest limit for shipping. Average content of glucose was lower in early heated vines and that of fructose was lower in unheated vines than normally heated ones, although there were wide variations among vines. Average malic acid content was highest in early heated vines and by further lowest in unheated vines. However, no significant difference was found in tartaric acid content among the vines. Concentrations of alanine and proline, major amino acids enhancing sweetness, were lower in early heated vines than in normally heated ones. In unheated vines, average concentration of proline was highest, although that of glutamine, a main factor enhancing deliciousness of the juice, was lowest. Threonine, an amino acid which at higher levels decreases sweetness, was detected at various levels depending on the vine. Geraniol, the second major substance of Muscut aroma, was found at significantly higher levels in early heated vines than in the other ones. The relationships between these compositions and the berry flavor were discussed.