In December 2018 researchers from the Russian Federation published the results of their analysis to assess the nutrient profile of grape juice. Grape juice is not highly acidic and contains on average 0.4 g of organic acids per 100 cm3, the major acids being` tartaric acid and L-malic acid. The presence of tartaric acid is a distinctive feature of grape juice as it is only found extremely rarely in other juices and, when it is, only in traces. Potassium, magnesium, iron, manganese, as well as flavonoids and hydroxycinnamic acids are the most important micronutrients and biologically active substances found in grape juice. Caftaric acid is the main hydroxycinnamic acid, the average level being 5 mg/100 cm3. One serving of grape juice contains, on average, 6-10% of the daily requirement for potassium and about 5-8% for magnesium, iron and manganese. The content of flavonoids per serving is about 25% of the daily requirement. Juice from red/purple grape varieties contain anthocyanins (on average 3 mg/100 cm3) and about 50% of these are malvidin glycosides. Resveratrol (an average of 0.01 mg/ 100 cm3), a stilbenoid, is also found in grape juice and this substance has a high antioxidant activity.
Ivanova NN et al. The nutritional profile of grape juice. Vopr Pitan. 2018;87(6):95-105.