Chemical and Sensory Evaluation of Blackberry (Rubus sp.) Juice Concentrated by Reverse Osmosis and Osmotic Evaporation.

Abstract

Blackberry can be considered a source of phenolic compounds with antioxidant properties, especially anthocyanins, which are responsible for the attractive color of the juice. However, blackberry juice quality can be reduced under severe heat treatments, resulting in darkened color and altered taste. Membrane separation processes are an alternative for the clarification and concentration of fruit juices, with advantages as the maintenance of the nutritional, sensory, and functional characteristics of the product. The aim of this work was to evaluate the effect of membrane concentration on the physicochemical and sensory characteristics of blackberry juice. The juice was first clarified by an enzymatic treatment associated with microfiltration and then concentrated by reverse osmosis and osmotic evaporation. Samples were analyzed for pH, titratable acidity, soluble and total solids, phenolic content, antioxidant activity, and total anthocyanins. The concentrated juices were then reconstituted for sensory evaluation. It was verified that reverse osmosis and osmotic evaporation resulted in juices with total solid concentrations of 29 and 53 g∙100 g^-1, respectively, with slight differences in pH and acidity. Some phenolic compounds were lost during processing. The concentration of anthocyanins and the antioxidant capacity of the osmotic evaporation-concentrated juice increased 6.2 and 7.7 times, respectively, compared to the initial juice. Regarding sensory analysis, the juices concentrated by RO and EO presented acceptance percentages (scores between 6 and 9) of 58% and 55%, respectively. Consumers described them as "good appearance", "refreshing", "tasty", "sweet", or "with ideal sweetness", in agreement with the high acceptance scores (6.2 and 6.9, respectively).