Quality of kiwifruit juice clarified by PEEK WC hollow fibre membranes

Modified poly(ether ether ketone) (PEEKWC) hollow fibre (HF) membranes were prepared via the dry-wet spinning technique through the phase inversion process and tested for the clarification of fresh depectinised kiwifruit juice. The aim of this work was to evaluate the quality of the clarified juice produced in experimental runs preformed according to the batch concentration mode in optimal operating conditions previously identified. Fresh juice, permeate and retentate samples were analysed for color, clarity, suspended solids content, total soluble solids (TSS), pH, acidity, viscosity, total antioxidant activity (TAA), total phenolics, vitamin C and organic acids (malic, succinic and citric). Results showed that suspended solids were completely removed by the membrane process and the resulting clarified juice showed a 16.6% loss in TSS concentration if compared with the feed. The titratable acids and pH of the juice were not influenced by the membrane treatment. The viscosity of the depectinised juice was reduced significantly (more than 50%) since suspended solids and pectinous materials were completely removed by the membrane. An improvement in color and clarity of juice was observed after the membrane treatment because of the removal of suspended colloidal particles and high molecular weight soluble solutes present in the juice. Organic acids and total phenols can be recovered in the clarified fraction of the juice due to the low rejection of the membrane towards these compounds. A 20.7% loss of ascorbic acid in the permeate was measured in comparison with the fresh juice so that the 23.6% decrease of the TAA in the permeate can be partially attributed to the degradation of this compound.