A membrane based process for the clarification and the concentration of the cactus pear juice quality

Cactus pear fruit is a food of nutraceutical and functional importance. Unfortunately, the low acidity and the high soluble solids content make the pulp of this fruit a very attractive media for growth of microorganisms requiring a thermal treatment (115.5 degrees C or higher) to obtain a good control of the microbial invasion. A relatively long thermal treatment (100 degrees C for 20 min) can produce a good microbiological stability; however the final product is characterised by an unattractive hay taste and does not resemble the original fresh juice due to changes in colour and flavour. The aim of this study was to study the potentiality of a membrane-based process for the clarification and the concentration of the cactus pear fruit juice. The fresh juice, with a total soluble solids (TSS) content of about 11 degrees Brix, was previously clarified by an ultrafiltration (UF) step, on laboratory scale, according to the batch concentration mode. The clarified juice was then concentrated by osmotic distillation (013) up to a TSS content of 61 degrees Brix at 28 degrees C. An initial evaporation flux of 1.16 kg/m(2) h was obtained using a calcium chloride dehydrate solution at 60 w/w% as stripper. The juice quality was analysed in terms of total antioxidant activity (TAA), ascorbic, citric and glutamic acid, betalains and viscosity in order to evaluate the effects of the membrane processes on the quality and composition of the juice.