Optimization of ultrasound-assisted extraction of phenols from seeds of grape pomace.

The aim of this research was to optimize the extraction condition of ultrasound-assisted extraction (UAE) of phenols from the red grape of Vranac variety (Vitis vinifera L.) pomace seeds. The minimum experiments needed for optimization of UAE by response surface methodology (RSM) were obtained by spectrophotometric and HPLC analyses of seed extracts. UAE greatly depends on three independent variables: extraction temperature, time and liquid/solid ratio. The RSM can be used for optimization of UAE conditions to obtain maximum responses such as extraction yield, TPC, (+)-catechin, (-)-epicatechin and proanthocyanidin content. The predicted values of the model were in accordance with experimental data under the same conditions (RSD was 0.74%). Experimental data also confirmed that UAE gives a better yield of phenolics than conventional solvent extraction (23.76% increase). The UAE under optimal extraction conditions is suitable for obtaining extracts that are rich in phenolic content, and have strong antioxidant activity which could be used as additives in food and medicaments.

Antioxidant and antimicrobial potentials of Serbian red wines produced from international Vitis vinifera grape varieties.

BACKGROUND: Antioxidant and antimicrobial potentials of Serbian red wines produced from different international Vitis vinifera grape varieties and their correlation with contents of phenolic compounds were studied by spectrophotometric and chromatographic methods. The antioxidant activity of red wines was estimated through their ability to scavenge 2,2'-diphenyl-1-picrylhydrazyl free radical (DPPH(•) ). The red wines, gallic acid, (+)-catechin and quercetin were screened in vitro for antimicrobial activity against Gram-positive and Gram-negative strains using microdilution and disc diffusion techniques. RESULTS: Excellent correlations between the contents of quercetin-3-glucoside (R(2) = 0.9463) and quercetin (R(2) = 0.9337) and DPPH(•) -scavenging ability of the red wines were found. Serbian red wines exhibited significant activity against Staphylococcus aureus, Listeria inocua, Micrococcus flavus, Sarcina lutea, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis and Shigella sonnei strains, which was in correlation with their phenolic composition and antioxidant activity. The compounds gallic acid, quercetin and (+)-catechin showed high activity against B. subtilis, S. aureus, S. lutea and M. flavus Gram-positive and S. enteritidis and P. aeruginosa Gram-negative strains. CONCLUSION: The results show that quercetin-3-glucoside and quercetin concentrations can be used as markers for the determination of antioxidant and antimicrobial potentials of red wines.

Phenolic profile and free radical-scavenging activity of Cabernet Sauvignon wines of different geographical origins from the Balkan region.

BACKGROUND: The phenolic profile, determined by the relative proportions of different phenolic compounds, is characteristic for each grape variety and its corresponding wine. The aim of this study was to determine the phenolic and hydroxycinnamate acid, flavan-3-ol and flavonol contents and free radical-scavenging activity of single-cultivar (Cabernet Sauvignon) wines from selected Balkan vineyard regions by spectrophotometric methods and high-performance liquid chromatography with photodiode array and fluorescence detection. RESULTS: The contents of phenolic compounds varied depending on the agroclimatic factors and oenological practices of the vineyard region. The antioxidant activity of wine samples was estimated by their ability to scavenge the stable 2,2'-diphenyl-1-picrylhydrazyl free radical (DPPH). All wines showed high DPPH-scavenging activity (70.03-83.53%, mean 73.76%). Significant correlations between catechin (R(2) = 0.8504) and quercetin (R(2) = 0.8488) concentrations and DPPH-scavenging ability of the wines were found. CONCLUSION: The concentrations of the main components catechin and quercetin can be used as biochemical markers for the authentication of red grape cultivars and their corresponding single-cultivar wines.