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In this study the applicability of membrane distillation (MD) was investigated to produce black-currant juice concentrate. For the experiments enzyme treated, pre-filtered by microfiltration and pre-concentrated by reverse osmosis fruit juice was applied. The measurements were carried out in a hollow fibre membrane contactor. Two different temperature differences were investigated as driving force: 15 and 198C. The shape of the curves of the fluxes appeared very similar at both temperature differences, however in case of the higher driving force the observed flux was 80% higher than in case of the lower driving force. By the MD process the pre-treated initial juice with 228Brix total soluble solid (TSS) content was concentrated up to 58.28Brix. Samples were collected during the concentration process and the density, total acid content (TAC) and anthocyanin content were measured. From the results it can be concluded that all the analysed parameters were directly proportional to the increase of the TSS in the juice. Due to the increase of the TAC the pH of the final concentration decreased under pH 0/2.

From the results of the experiments it can be concluded that the MD is capable of the concentration of black-currant juice up to a high solid content. The final concentration of the blackcurrant juice reached 58.28Brix at the end of the batch measurements. This high concentration prevents the juice from deterioration. It has been found that a few degree centigrade increase in the driving force influenced significantly the distillate flux and the operation time of the MD process. During the concentration the distillate flux slowly decreased till the end of the process due to a decrease in the driving force and the Re number of the concentrate. The result of the analytical measurements shows that the density, TAC and AC of the black-currant juice increase proportionally to the increase of the TSS in the measured range. Comparing the results of the concentration of black-currant juice with the results of the concentration of grape juice with MD, it was observed that there were no significant differences in the permeate fluxes using the same driving force (temperature difference) [5].