Influence of harvesting dates on rate of drying, recovery, quality and sensory evaluation of raisins prepared from seedless varieties of grape (Vitis vinifera L.)

Abstract

A study was conducted at Grape Research Station, Hyderabad, to study the effect of harvesting dates on rate of drying, recovery, quality and sensory evaluation of raisins prepared from five seedless varieties of grapes. Selected grape bunches of Thompson Seedless, 2A Clone, Sonaka, Manik Chaman and Merbein Seedless were manually harvested on 9th, 12th, 14th, 17th and 21st March, respectively as first harvest date was chosen as simultaneous with the beginning of the 20 days before local harvest. Succeeding harvests i.e. second (10 days before local harvest), third (local harvest), fourth (10 days after local
harvest) and fifth (20 days after local harvest) was done with 10 days interval following the first harvest date. The grapes were dried in ventilated rooms after pre-drying treatment with alkaline emulsion of ethyl oleate (2.4% K2CO3 + 1.5% ethyl oleate) with ascorbic acid 1000 ppm. Results showed that the raisins prepared from well matured grapes i.e. harvested between 19th April to
1st May (20 days after local harvest) recorded maximum rate of drying and average raisin weight. Significantly highest raisin recovery of 26.20% was recorded in Thompson Seedless variety harvested on 19th April (20 days after local harvest). The sensory attributes and quality parameter like brix-acid ratio, ascorbic acid, sugar (total, reducing and non-reducing) content of raisins increased with successive harvest dates and highest values recorded in late harvest. Thompson Seedless raisins were superior compared to all other varieties. From this finding it can be concluded that the raisins prepared from fully ripened grapes i.e. Thompson Seedless harvested on 9th to 19th April and Manik Chaman on 17th to 27th April (between fourth and fifth harvest) in
Hyderabad conditions were superior for studied characters