Processing and chemical composition of rhubarb (Rheum rhabarbarum) juice

Abstract

A simple and effective processing method for rhubarb stalks including washing, comminution in a perforated disk mill followed by immediate dejuicing of the mash is presented. Rhubarb is an easy to process vegetable which does not necessarily need a special mash treatment like enzymation or heating to get high juice yields. The chemical composition of rhubarb juice is characterised by a low relative density and low Brix (4–4.8 °Brix), due to a low sugar content (about 12 g/l), whereas the total acidity is high (about 17 g/l). The major acid is malic acid, followed by oxalic acid and citric acid. The polyphenol content and the antioxidative capacity (TEAC) is relatively low; the same holds for anthocyanins (11.3–14.8 mg/l) which are consisting of cyanidin-3-rutinoside and small amounts of cyaniding-3-glucoside and delphinidin-3-rutinoside. Rhubarb juice contains a high amount of minerals, esp. potassium (up to 4000 mg/l), and magnesium (average 100 mg/l), whereas calcium is not present due to precipitation with oxalic acid. As is the case for some other vegetables juices, rhubarb juice contains high concentrations of nitrate (about 850 mg/l).