Chemical composition of dietary fiber and polyphenols of five different varieties of wine grape pomace skins

The skins of two white wine grape pomace (WWGP) and three red wine grape pomace (RWGP) from US Pacific Northwest were analyzed for their dietary fiber (DF) and phenolic composition. OF was measured by gravimetric-enzymatic method with sugar profiling by HPLC-ELSD. Insoluble DF composed of Klason lignin (7.9-36.1% DM), neutral sugars (4.9-14.6% DM), and uronic acid (3.6-8.5% DM) weighed more than 95.5% of total DF in all five WGP varieties. WWGP was significantly lower in DF (17.3-28.0% DM) than those of RWGP (51.1-56.3%), but extremely higher in soluble sugar (55.8-77.5% DM vs. 1.3-1.7% DM) (p<0.05). Soluble polyphenols were extracted by acidified 70% acetone and measured spectrophotometrically. Compared with WWGP, RWGP had higher values in total phenolic content (21.4-26.7 mg GAE/g DM vs. 11.6-15.8 mg GAE/g DM) and DPPH radical scavenging activity (32.2-40.2 mg AAE/g DM vs. 20.5-25.6 mg AAE/g DM) (p<0.05). The total flavanol and proanthocyanidin contents were ranged from 31.0 to 61.2 mg CE/g DM and 8.0 to 24.1 mg/g DM, respectively for the five WGP varieties. This study demonstrated that the skins of WGP can be ideal sources of DF rich in bioactive compounds. (C) 2011 Elsevier Ltd. All rights reserved.