TY - JOUR T1 - Diurnal Changes of Amino Acid Concentrations in Riesling and Chardonnay Grape Juices and Possible Role of Sunlight JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. DO - 10.5344/ajev.2014.13144 SP - ajev.2014.13144 AU - Lin Wang AU - Jun Harada AU - Yuka Endo AU - Masashi Hisamoto AU - Fumie Saito AU - Tohru Okuda Y1 - 2014/07/21 UR - http://www.ajevonline.org/content/early/2014/07/16/ajev.2014.13144.abstract N2 - Diurnal changes in the concentrations of amino acids in grape juice were investigated during the mid- to late-ripening period over three consecutive years. To avoid the effect of harvest shock, samples were prepared within 15 min after grape berry picking. Changes in the amino acid concentrations of juices were classified into three patterns. The concentrations of aspartic acid (Asp) and glutamic acid (Glu) decreased during the morning and gradually increased at nighttime. Alanine (Ala) concentration increased during the morning and decreased at nighttime. The amino acids peak times were 0600 to 0900 for Asp, 0600 to 0700 for Glu, and 1300 to 1900 for Ala for Riesling harvested from 31st AUG to 1st SEPT 2010. Some of the other amino acids (such as phenylalanine, serine, proline, and threonine) showed minimal or no diurnal changes in concentration. Yeast assimilable nitrogen (YAN) showed minimal daily changes. During cloudy days, these diurnal changes were diminished. When grape clusters were shaded with aluminum foil, the patterns of amino acid levels did not change, with some exceptions. Photosynthesis is proposed as the main contributor to these changes, since minimal changes were observed under cloud cover. Moreover, leaf rather than berry photosynthesis is likely an important factor in the composition of berry amino acids. ER -