Effects of bud load on quality of Beogradska besemena and Thompson seedless table grapes and cultivar differentiation based on chemometrics of analytical indices.

Background: The effects of bud load on the quality of Beogradska besemena and Thompson seedless table grape cultivars were studied. Two pruning treatments were imposed: 44 and 18 buds per vine for Beogradska besemena and 44 and 22 buds per vine for Thompson seedless.

Results: In Beogradska besemena the reduction of bud load decreased titratable acidity (-4%), skin dry weight (-16%) and malic and citric acid contents (-43 and - 20%) and increased tartaric acid content (14%). The decrease in pulp antioxidant activity (-36%) was related to the decrease in hydroxycinnamoyl tartaric acid content (-13%). Concerning skin, the reduction of bud load decreased catechin and caffeoyl tartaric acid contents (-42 and - 40%) and significantly increased rutin and quercetin-3-O-glucopyranoside contents as specific compounds and flavonoids and proanthocyanidins (9 and 21%) as classes of compounds, thus causing an increase in antioxidant activity (6%). In Thompson seedless the reduction of bud load increased soluble solid content (7%), acidity (9%) and concentrations of the three organic acids (7, 3 and 14%). The increase in pulp antioxidant activity (25%) could be attributed to the increase in total phenolics (69%). The reduction of bud load caused a significant decrease in quercetin-3-O-glucopyranoside (-26%) and antioxidant activity (-15%) in skin. Principal component analysis allowed good separation between samples of the two cultivars, independently of bud level.

Conclusion: The results indicate that the effects of different bud loads are cultivar-dependent. Bud load and genotype differences were shown to dramatically impact the quality and antioxidant properties of table grape.