Concentration of clarified kiwifruit juice by osmotic distillation

Abstract

This study was undertaken in order to evaluate the potential of the osmotic distillation (OD) process for concentrating clarified kiwifruit juice on laboratory scale, taking into account the impact on the product quality especially in terms of ascorbic acid content and total antioxidant activity (TAA). The performance of the OD process in terms of flux and concentration factor was also evaluated. The clarified juice, with an initial TSS content of 9.4°Brix, was concentrated up to final values of 66.6°Brix, by using a laboratory bench plant equipped with a Liqui-Cell ® Extra-Flow 2.5 × 8 in. membrane contactor realised with polypropylene hollow fiber membranes. Calcium chloride dihydrate at 60 w/w% was used as stripping solution producing an initial evaporation flux of about 1.3 kg/m 2 h. The experimental data indicates that at low total soluble solids (TSS) concentration the evaporation flux decay is more attributable to the dilution of the stripping solution while, starting from a TSS value of 35°Brix, the evaporation flux depends mainly on juice viscosity and, consequently, on juice concentration. The analytical measurements showed that the OD process has no influence on the acid ascorbic content independently by the concentration degree achieved, while in the retentate at 66.6°Brix obtained by thermal evaporation a reduction of 87% of Vitamin C was observed with respect the clarified juice. Also the TAA of the clarified juice was maintained constant during the osmotic distillation process while a reduction of 50% of this activity was detected in the retentate samples coming from the thermal treatment. On the basis of the experimental results an integrated membrane process for the clarification and concentration of kiwifruit juice was proposed.