Effect of harvest time on table grape quality during on-vine storage

Postponing the harvest of grapes is a common practice in southern Italy, in order to delay harvest up to Christmas and make higher income from their sale. The aim of this work was to evaluate the effect of harvest time (over almost 3 months) on the quality of table grapes (cv. Italia). The experiment was repeated for two years (2010 and 2011). In 2010, grapes were harvested starting from 8 October and after 11, 27 and 48 days. In 2011, five harvest times were compared over a period of 56 days. Respiration rate, firmness, colour, sensory attributes, total soluble solids (TSS), pH, titratable acidity (TA), phenols and antioxidant activity were measured. In addition, in the second year, volatile compounds were evaluated.

For both years, harvest time influenced most parameters, which indicated that metabolic changes took place in the plants. In 2010, harvest time influenced respiration rate, cluster and berry appearance scores, colour attributes, crunchiness, pH, TA, total phenol content and antioxidant activity. In 2011, harvest time influenced respiration rate, colour attributes, most sensory attributes, TSS and TA. Generally, late harvested grapes showed higher firmness, berry appearance score, sweetness, fruity taste, overall sensory evaluation score and TSS. Regarding volatile compounds, terpene content decreased during ripening, while C6 compounds showed a nonlinear trend.

The results showed that table grape sensory quality could be increased by delaying harvest up to a certain time of the season, while excessive delay could reduce final grape quality.