Athermal concentration of fruit juices by osmotic distillation: performance and impact on quality

The concentration of fruit juices is a fundamental factor for the competitiveness of products as it reduces costs related to operation logistics (packing, storage and transport) and improves the microbiological stability. It is known that removal of water from the juices by using the classic thermal evaporation degrades sensorial properties and nutritional compounds such as vitamins leading to a partial loss of the fresh juice flavor. In the recent years the consumers interest for healthier and more natural products has led to numerous research efforts able to improve the quality of fruit juices by using technological alternatives to thermal processing. Membrane processes, such as nanofiltration, reverse osmosis and osmotic distillation, represent a promising alternative for processing fruit juices mainly due to the possibility of operating at moderate temperatures. However, the main disadvantage of baromembrane processes is their inability to reach the standard concentration produced by thermal evaporation (650-700 g/kg of total soluble solids) because of high osmotic pressure limitation. Osmotic distillation is an interesting alternative for the concentration of thermosensitive solutions, such as liquid and pharmaceutical products, because it works under atmospheric pressure and room temperature, thus avoiding thermal and mechanical damage of the solutes. This work highlights the potential of using osmotic distillation in the concentration of different clarified fruit juices such as red orange, cactus pear, kiwifruit and pomegranate juice. The process is evaluated in terms of performance and impact on product quality. In particular, the main physic-chemical properties of concentrated products, including phenolic compounds and antioxidant activity, were evaluated and compared with those of fresh and thermally concentrated juices.