Chemical composition, nutritional and in vitro functional properties of by-products from the Brazilian organic grape juice industry

Grape juice and wines (Vitis sp.) are the products that are most produced and consumed from different varieties of grapes. About 20% of pomace is generated from processing but there are very few products available with added grape pomace. Consequently, the aim of this study was to characterize flours made from grape skin (GSF) and grape pomace (GPF: seeds + skin) from organic Vitis labrusca L. cv. Bordeaux with respect to physicochemical composition, bioactive compounds content and antioxidant/reducing capacities. The by-products presented a high content of insoluble fibers (55.84 +/- 0.63 and 51.02 +/- 1.12 g/100 g, respectively); total lipids contents below 10 g/100 g; and >1.900 mg gallic acid equivalent (GAE)/100 g total phenolic content, in which total ortho-diphenols, flavonols, anthocyanins and water-soluble condensed tannins were the main chemical compounds. Regarding the in vitro functionality, which was measured by chemical methods, the GPF and GSF presented values of 1373.64 +/- 72.94 and 361.48 +/- 2.99 mg GAE/100 g iron reducing capacity; 1574.26 +/- 8.94 and 1499.79 +/- 31.39 mg ascorbic acid equivalent/100 g in the reduction of DPPH radical; and 2892.46 +/- 61.69 and 426.34 +/- 18.85 mg of quercetin equivalent/100 g of total reducing capacity, respectively. The results indicate that the GPF and GSF produced from the organic grape juice industry are promising materials for use by food companies. (C) All Rights Reserved