Journal
FOODS
Volume 9, Issue 5, Pages -Publisher
MDPI
DOI: 10.3390/foods9050604
Keywords
grape stem; phenolic compounds; central composite rotatable design; antioxidant activity; sustainable food systems; pressurized liquid extraction; side streams valorisation
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Funding
- Comunidad Autonoma de Madrid (ALIBIRD) [P2013/ABI2728]
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Pressurized liquid extraction with ethanol:water mixtures was proposed for obtaining phenolic antioxidants from grape stems. The optimal extraction conditions were elucidated by using a central composite rotatable design (solvent (X-1, 0-100% ethanol:water v/v), temperature (X-2, 40-120 degrees C) and time (X-3, 1-11 min)). Response surface methodology determined 30% ethanol:water, 120 degrees C and 10 min as the optimal extraction conditions regarding total phenolic content (TPC) (185.3 +/- 2.9 mg gallic acid/g of extract) and antioxidant activity (3.55 +/- 0.21 mmol Trolox/g, 1.22 +/- 0.06 mmol Trolox/g and 1.48 +/- 0.17 mmol Trolox/g of extract in ABTS, DPPH and ORAC methodologies, respectively). The antioxidant activity was attributed to total polymer procyanidins and flavan-3-ol monomers and oligomers, although other phenolic compound contributions should not be ruled out. Forty-two phenolic compounds were identified in the optimal extract, mainly polymer procyanidins and, to a lesser extent, monomers and oligomers of flavan-3-ols, quercetin-3-O-glucuronide, epsilon-viniferin, gallic and caftaric acid. Ethyl gallate, ellagic acid, protocatechuic aldehyde, delphinidin-7-O-glucoside and cyanidin-3-O-glucoside were reported for the first time in grape stem extracts. In conclusion, this study highlights the use of this winery side stream as a source of antioxidants within a sustainable food system.
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