RESUMO
The phenolic compounds play an important role in production of quality grapes and wines. The current investigation focused on optimization of an extraction method for targeted analysis of 33 phenolic compounds in grapes by liquid chromatography tandem mass spectrometry (LC-MS/MS). The optimized method was successfully used for phenolic profiling of two wine grape varieties, Sauvignon blanc (white) and Shiraz (red) originated from Pune and Nasik regions of Maharashtra State, India. The optimized sample preparation procedure involved liquid-liquid extraction with acidified methanol by vortexing for 2 min followed by analysis on LC-MS/MS. The limit of quantification of the targeted compounds was in the range of 29 to 411 µg/L. The results indicated that skin of both varieties contained the highest amount of flavonols (69.47 ± 14.74 mg/kg in Sauvignon blanc and 129.47 ± 10.05 mg/kg in Shiraz) compared to pulp. The highest amounts of flavan-3-ols were present in grape seed collected from the Pune region (2016.84 ± 14.73 mg/kg in Sauvignon blanc and 1945.06 ± 32.69 mg/kg in Shiraz). The concentration of stilbenes was the highest in grape skin (0.13 ± 0.52 to 5.78 ± 5.45 mg/kg) compared to seed and pulp of both varities. Hydroxybenzoic acid (vanillin), hydroxycinnamic acid (p-coumaric acid) and anthocyanins (oenin, malvidin, cyanidin and kuromanin) were found only in Shiraz variety. The results of antioxidant activity (FRAP and DPPH assay) indicated the highest scavenging activity in seed (978.64 ± 56.23 to1133.38 ± 143.65 µMol TE/g DW FRAP and 594.93 ± 37.94 to 631.94 ± 56.45 µMol TE/g DW in DPPH). The phenolic contents in Sauvignon blanc and Shiraz grapes between Pune and Nasik regions did not have any significant difference.
