Phenolic compounds and antioxidant activity of experimental and industrial table grape juices

Phenolic compounds are the third most abundant constituents in grapes and derivatives and are known to contribute to human health due to their antioxidant and anti-mutagenic effects and their ability to prevent pathologies such as cancer and cardiovascular diseases. Grapes and derivatives are among the most important sources of phenolics. The purpose of the present work was the evaluation of these compounds in experimental and industrial grape juices. Additional physico-chemical indices were also evaluated in order to complete the juices characterization. The experimental juices were separately produced from Italia and Red Globe table grapes cultivars by centrifugation and crushing. Three types of industrial grape juices (Italia cv.) were considered: A juice with medium sugar content; a juice with high sugar content; a strongly sulphited juice. Analyses were performed on the starting grapes and on the unpasteurized juices. The results showed a noticeable loss of phenolics during extraction although crushing was more efficient than centrifugation. In fact, the juices obtained by crushing showed higher phenolic contents than the juices obtained by centrifugation (16%–19% more total phenolics, 16%–31% more flavonoids, 7%–11% more flavanols reactive with vanillin, 100% more proanthocyanidins). Strong correlations among total phenolics and antioxidant activity of grapes and flavanols reactive with vanillin and antioxidant activity of juices were observed. The extraction methods significantly affected physico-chemical characteristics and antioxidant contents of the resulting juices since centrifugation mainly acted on pulps, while trituration involved the whole grape berries.