Abstract
Grapes are widely known for health benefits due to their antioxidant content. In wine production, grape stems are often discarded, though they has a higher content of antioxidants than the juice. The effectiveness of using an environmentally friendly solvent, ethanol, as a superheated liquid and supercritical fluid to extract antioxidant compounds from grape stems of organically grown Crimson Seedless grapes was evaluated. The Ferric Reducing Ability of Plasma (FRAP) assay and the Total Phenolic Content (TPC), or Folin-Ciocalteu assay, were used to quantify the antioxidant power of grape stem extracts. The extractions were performed at temperatures between 160°C and 300°C at constant density. It was found that the optimal extraction temperature was 204°C, at superheated liquid conditions, with a FRAP value of 0.670mmol Trolox Equivalent/g of dry grape stem. The FRAP values were higher than other studies that extracted antioxidants from grape stems using single-pass batch extraction.
Highlights
Grapes are the most commonly grown fruit in the world with over 67.1 million tons grown in 2010 (Ghafoor et al 2012)
The antioxidant ability of superheated liquid and supercritical ethanol extraction of dried grape stems was characterized for effects of temperature, hold time, and effects of morphology by comparing ground and whole grape stems
The density of ethanol was chosen in order to ensure that it is a superheated liquid or a supercritical fluid, depending on temperature
Summary
Grapes are the most commonly grown fruit in the world with over 67.1 million tons grown in 2010 (Ghafoor et al 2012). Grape pomace, consisting of seeds, peels, and stems, is often discarded as waste. Like many fruits, the highest concentration of antioxidants in grapes does not occur in the pulp, the origin of most of the antioxidant compounds of wines and juices. Seeds of the red rose grape have 100 times the antioxidant power and the peel contains 20 times the antioxidant power compared to pulp (Guo et al 2003). Though not as frequently studied, grape stems contain phenolic compounds and exhibit similar antioxidant power as grape seeds (Souquet et al 2000; Anastasiadi et al 2009). Grape stems present stable economic potential since they exhibit antioxidant power and are ordinarily discarded during processing
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