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High Hydrostatic Pressure Extraction of Flavonoids from Freeze-Dried Red Grape Skin as Winemaking By-product

INTRODUCTION: Winemaking by-products, such as grape pomace, are an inexpensive and rich source of phenolic compounds with well recognized health benefits. Aside from sample preparation, extraction procedure has a significant impact on the recovery of phenolic compounds from plant material. Recent studies showed that innovative technologies, such as high pressure processing, has the potential to enable the greater yield of target phenolic compounds compared to existing technologies. Hence, high hydrostatic pressure extraction (HHPE) has proven to effectively shorten the extraction time, improve the mass transfer rate, and enhance solvent permeability in cells as well as secondary metabolite diffusion. OBJECTIVES: The optimal operating conditions for the HHPE of flavonoids from freeze-dried red grape skin pomace (cv. Teran) have been investigated. The aim was to obtain extracts with high flavonoid recovery and high antioxidant capacity. METHODS: Extractions of were carried out in methanol at different polarity (30, 50 and 70%, v/v), under various pressures (300, 400 and 500 MPa) during 3, 6.5 and 10 min. The total flavonoids (TF) were measured spectrophotometrically by using the aluminium chloride colorimetric assay and quercetin as calibration curve. FRAP method were used for assaying the antioxidant capacity (AC) and ascorbic acid as calibration curve. RESULTS: Parameters such as time, pressure, and solvent polarity showed remarkable effects on TF yields. Grand mean value for flavonoids was 160.63±2.81 mg quercetin equivalents/100g. Flavonoids extraction was not influenced by HHPE while with increased polarity increased amounts of this compounds in the extracts. CONCLUSION: HHPE provided effective method for TF extraction from red grape skin as winemaking by-product thus could have potential application benefits in industry.

High hydrostatic pressure extraction; total flavonoids; antioxidant capacity; grape skins; winemaking by-products

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