Processing of Red Dragon Fruit Juice by Membrane-Based Operations: A Key Factor in Obtaining Concentrated Fractions...

Red dragon fruit (Hylocereus polyrhizus), also referred to as pitaya, is an exotic fruit rich in macro- and micro-nutrients, including powerful natural antioxidants, that brings numerous benefits to human health, mostly for the control and management of the oxidative stress. Therefore, it has a great potential for industrial exploitation aimed at maximizing the extraction of its high-value bioactive compounds, specifically betacyanins (red pigments) and phenolics, for the production of functional foods, beverages, and health products. This aim of this study was to evaluate the production of high-quality concentrated red dragon fruit juice by using an integrated membrane system based on a combination of ultrafiltration (UF) and osmotic distillation (OD) processes capable of effective, but still mild concentration of valuable juice. Specifically, after juice extraction, the raw juice was preliminarily clarified by UF and then concentrated by OD up to 41 and 50 °Brix using dehydrate calcium chloride brine as the osmotic agent. The performance of UF and OD membranes was investigated under selected operating and hydrodynamic conditions. In addition, the impact of the integrated process on the quality of clarified and concentrated juices was assessed in terms of physicochemical properties and antioxidant activity. Physicochemical parameters and antioxidant activity were largely preserved after concentration, demonstrating the effectiveness of the proposed process in maintaining the nutritional, organoleptic, and nutraceutical properties of the juice.