Physicochemical characterisation, bioactive compounds and in vitro antioxidant activities of commercial integral grape juices

Integral grape juice is an unfermented drink prepared from the edible part of grapes, with no water or sugar added. Besides commercial interest, several nutritional benefits for consumers’ health have been associated with the regular consumption of grape juice which helps to consolidate its popularity among Brazilian consumers. In the present work, ten different commercial integral grape juices, eight from red grape and two from white grape were analysed for their physicochemical properties, including pH, °Brix, density, colour, total phenolic content, anthocyanins, and ABTS and DPPH antioxidant activities. All samples had a pH of 3.02 to 3.27, 13.9 to 15.2°Brix, and a density of around 1.06. However, there were significant differences in colour intensity, which varied from 5.89 to 22.42 AU (red grape juices) and from 0.333 to 0.395 AU (white grape juices). Phenolic contents of 0.790 to 1.774 mg GAE/ mL were detected in red grape juices, and 0.193 to 0.343 mg GAE/mL from white grape juices. While anthocyanins were not identified in white grape juices, their values ranged from 19.87 to 101.61 mg/L in red grape juices. High antioxidant activities were found in all samples, but white grape juices showed significantly less activity as compared to red grape juices. Red grape juices showed DPPH values of 52.46–103.98 and 11.57–17.09 mM TEAC/mL, and ABTS values of 201.30–423.94 and 60.96–79.87 mM TEAC/mL for red and white grape juices, respectively. Based on these results, it is possible to conclude that grape juices, especially from red grapes, can provide important quantities of natural antioxidant molecules, such as polyphenols, including anthocyanins, which strongly act to neutralise free radicals.