Impact of extraction conditions on the phenolic composition and antioxidant capacity of grape stem extracts

Can discarded winery waste become a goldmine for powerful antioxidants? Researchers are unlocking the secrets of grape stems to fuel the pharmaceutical, food, and cosmetic industries.

Grape stems are no longer just vineyard trash. By carefully tuning extraction conditions like temperature, ethanol concentration, and sample-to-solvent ratios, scientists are extracting valuable bioactive compounds from Mazuelo grape stems. It turns out that ethanol concentration is the master knob controlling the whole process.

When scientists tested various combinations, the sweet spot for maximizing total phenolic compounds and antioxidant activity was remarkably clear: a 50 percent ethanol solution operating at 40 degrees Celsius. While water successfully coaxed out the maximum amount of gallic acid, the 50 percent ethanol mix proved victorious for the extraction of most other compounds.

Looking closer at the chemistry, (+)-catechin emerged as the most abundant compound in the extracts, alongside gallic acid, a quercetin derivative, and stilbenes like trans-resveratrol and trans-ε-viniferin. Interestingly, quercetin and malvidin-3-glucoside drove the antioxidant capacity, while stilbenes sat that correlation out. Ultimately, the right extraction method depends entirely on which specific compound you want to capture.

Key Points

• Ethanol concentration is the most influential extraction factor
• 50 percent ethanol and 40 °C maximize phenolic compounds
• Quercetin and malvidin-3-glucoside correlate with antioxidant capacity