Solid Foodstuff Supplemented with Phenolics from Grape: Antioxidant Properties and Correlation with Phenolic Profiles

Abstract

Osmotic dehydration was assessed as an operation for supplementing a solid foodstuff (a gel was used as the model food) with grape phenolics from a concentrated red grape must to increase its antioxidant properties. The model food was processed for up to 24 h, and the osmotic pressure was adjusted by diluting the concentrated red grape must. In all conditions tested, low molecular weight phenolics (<or=610 g/mol) and, in particular, trans-caftaric acid, trans-coutaric acid, ferulic acid, coumaric acid, caffeic acid (hydroxycinnamic acids), gallic acid (hydroxybenzoic acids), quercetin, and rutin (flavonols), were quantified in the red grape must and also in the osmo-dehydrated food. Other flavonoids such as (+)-catechin and (-)epicatechin (flavan-3-ols) were detected only in the red grape must. Trolox equivalent antioxidant activity (TEAC) and ferric reducing antioxidant power (FRAP) were determined in the osmo-dehydrated food. Under the conditions that maximized phenolic infusion, the total phenolic content of the gel was close to the values reported in some rich-in-phenolic fruits and vegetables, whereas TEAC was 3 times that of fresh fruit with the highest antioxidant capacity. Regression analysis showed that the individual phenolics analyzed significantly explain the antioxidant capacity of the osmo-dehydrated food.