Processing of black carrot juice by nanofiltration and forward osmosis

Juice concentration is traditionally achieved with thermal evaporators. However, many nutrients and sensorial attributes suffer from degradation at high temperature. In order to preserve the sensorial and nutritional attributes of the juice, non-thermal processes based on membranes have arisen as an alternative. In the present work, 6.7 Brix black carrot juice has been subjected to a sequence of processes based on nanofiltration (NF) and forward osmosis (FO) operated at room temperature with the aim of concentrating acylated anthocyanins. Four polymeric membranes with molecular weight cut-offs in the range 150 - 2000 Da were compared in terms of flux and anthocyanin rejection. The membrane showing the best performance was a polyamide thin film composite NF membrane with a reported cut-off of 600 - 800 Da. With this membrane, the rejection of anthocyanins was 98% and the rejection of total soluble solids was 65 %. The juice was preconcentrated to 10 Brix with minimal anthocyanin loss. The resulting retentate was further concentrated to 43 Brix using FO biomimetic membranes and a solution of MgCl2 as draw.