Comparative Compositional and Biological Properties of Muscadine and Cabernet franc Grape Skins

Abstract

Numerous studies have documented the health benefits of moderate consumption of wines, and especially red wines. Much of this activity has been attributed to the extraction of phytochemicals from the skin and seeds during on-skin fermentation procedures. This study focused on the extraction and biological properties of phytochemicals from freeze dried skins of muscadine and Cabernet franc. The Cabernet franc grapes are a good source of resveratrol whereas muscadine grapes are an excellent source of ellagic acid with the resveratrol content varying considerably from batch to batch. Both grapes contain a complex mixture of phytochemicals, many of which have been shown to have potential health benefits in vitro. The skins of two muscadine cultivars, Carlos and Noble, and the skins of Cabernet franc grapes obtained during two harvests were freeze-dried, extracted with 80:20 methanol-water, and analyzed for antioxidant capacity followed by high pressure liquid chromatography (HPLC) and HPLC coupled with time of flight mass spectrometry (HPLC-TOF-MS) analyses for phenolic compounds. The anticarcinogenic activity of extracts was determined against LNCaP prostate carcinoma cells with the XTT proliferation assay and the caspase-3 assay used to determine apoptosis.

The 2006 Cabernet franc extract contained 70.3 μg/g resveratrol and no ellagic acid, whereas muscadine extracts contained 4.2-12.2 μg resveratrol and 117-269 μg ellagic acid per g dried sample. Neither resveratrol nor ellagic acid was detected in the 2007 Cabernet franc extract. The antioxidant capacity was measured using the oxygen radical absorbance capacity (ORAC) assay. ORAC values of grape skin extracts ranged from 110-354 μmol Trolox equivalents per g dried sample with Carlos being the lowest, followed by Cabernet franc, and Noble being the highest. At concentrations of 5 mg/mL, all skin extracts induced apoptosis in LNCaP cells as the increases in caspase-3 and other closely related proteases were significantly different from the controls. LNCaP proliferation was also inhibited at doses of 5 mg/mL. This study shows that even though the phytochemical composition of muscadine and Cabernet franc differ considerably, as by products of the winemaking industry, they both may have economic and potential health benefits as dietary supplements.