Optimization of the ultrasound-assisted extraction of polyphenols from Aronia and grapes

The extraction of phenolics and tannins from cold-hardy grapes is not maximized with the current methods, which lead to unbalanced wines. This study aims to investigate high-power sonication to improve polyphenolic content in cold-hardy grape juice in comparison with chokeberry juice. Three solid to solvent ratios and times were applied on chokeberry and 'Marquette' grape berries using 50% ethanol or 13% acidified ethanol and compared to a conventional extraction technique. Iron-reactive phenolic compounds, tannins content, and color were analyzed during the extractions using UV-Visible spectrophotometry, and anthocyanin content was analyzed using HPLC-DAD. At the 1:2 solid to solvent ratio, the color intensity, phenolics, and tannins content were improved using the ultrasound-assisted extraction on chokeberries. However, the tannin content of 'Marquette' berries remained the same with both techniques and solvents, suggesting that the plant cell wall structure may have a strong impact on the retention of tannins from cold-hardy grapes.