Athermal concentration of red fruit juices by osmotic distillation

Over the last years there have been many changes in the juice beverage market as consumers search for new benefits from their juices. As a result, an increase in demand occurred for red fruit juices, considered as healthy fruit beverages due to their higher phenolic compounds concentration, namely in flavonoids and non-flavonoids and consequently with high antioxidant activity. These red fruit juices could be used to design or develop new products that meet consumers' requests. The application of membrane technologies to support the production of innovative fruit juices fits well with the new strategies of sustainable food processing (SFP), based on the use of low energy and low impact environmental processing schemes. Moreover, thanks to mild operating conditions, the membrane treatment does not deteriorate the product quality as much as traditional thermal processing. In the present work the concentration of red fruit juices by osmotic distillation (OD) was investigated. A mix of pomegranate, cactus pear and blood orange juice previously clarified by ultrafiltration and then pre-concentrated by nanofiltration up to 33 °Brix was concentrated up to 60 °Brix by using a laboratory OD plant. The unit featured a Liqui-Cell Extra-Flow 2.5 x 8-in. membrane contactor (3M, Charlotte, USA) containing microporous polypropylene hollow fibers with an average pore diameter of 0.2 ?m and a total membrane surface area of 1.4 m2. The juice was pumped through the shell side of the membrane module; a 10.2 mol L-1 calcium chloride dehydrate solution, used as stripping solution, was pumped through the fiber lumens (tube side). At isothermal conditions (25±2 °C) transmembrane vapour water flux decreased from 0.75 to 0.2 kg h-1 m-2 when total soluble solids of the juice reached 60 °Brix (Figure 1a). This reduction is mainly associated to the dilution of the brine solution (Figure 1b) which in turn leads to the decrease in vapor pressure of the osmotic agent and, consequently, of the driving force for water transport from the feed through the membrane. In addition, the increase in total solids promotes the increase in the juice viscosity, which is also one of the causes for the reduction of the permeate flux. Other investigations are in progress in order to optimize the operating conditions of the process and to evaluate the OD performance in relation to the preservation of valuable compounds of the raw juice.