Effect of Harvesting Dates on Yield, Color and Quality of Raisin Prepared from Seedless Grape (Vitis vinifera)

Aims: To know the effect of harvesting dates on yield, color and quality of raisins prepared from seedless varieties of grapes viz., Thompson Seedless (TS), 2A Clone (2AC), Sonaka (SO), Manik Chaman (MC) and Merbein Seedless (MS).

Study Design: Factorial completely randomized design.

Place and Duration of Study: The present investigation was conducted at Grape Research Station, Rajendranagar, Hyderabad, Ranga Reddy district, Dr. Y. S. R. Horticultural University, during 2012–13 and 2013–14.

Methodology: Selected grape varieties viz., TS, 2AC, SO, MC and MS were manually harvested on 9th, 12th, 14th, 17th and 21st March, respectively, chosen as first harvest date i.e. 20 days before local harvest. Succeeding harvests i.e. second, third, fourth and fifth was done with 10 days interval following the first harvest date and used for raisin making. The grape bunches were dried in ventilated rooms after pre-drying treatment with alkaline emulsion of ethyl oleate (2.4% K2CO3 plus 1.5% ethyl oleate) with ascorbic acid 1000 ppm.

Results: Well matured grapes, which are harvested between 19th April to 1st May (20 days after local harvest) recorded lowest brown and mixed colored raisins and correspondingly increased green colored raisins. The grapes dried early in variety MS and it takes only 13.27 days followed by 2AC, TS, MC and SO in order. Raisin yield, size, texture, color homogeneity, total soluble solids, and Hunter color L*, -a* (greenness) and b* values increased with successive harvest dates. TS raisins were superior compared to others. The moisture content of raisins was lowest in fully matured (19th April to 1st May) grapes.

Conclusion: Raisins prepared from fully ripened grapes i.e. harvested between 9th to 19th April for Thompson Seedless and 17th to 27th April for Manik Chaman was superior regarding yield, retention of green color and quality.