Strategy for economical optimisation of the clarification of pulpy fruit juices using crossflow microfiltration

Microfiltration, using a mineral tubular membrane with nominal pore diameter of 0.2 mum, was applied to six tropical fruit juices (mango, pineapple, naranjilla, Castillas blackberry, passion fruit, tangerine) after partial enzymatic liquefaction. For passion fruit juice, it was found that, when estimating the total costs of producing clarified juice to volumetric reduction ratio (VRR) specifications, a VRR exists at which these costs are minimal. Nevertheless, for juices with a high pulp content, these optimal economic costs are reached at relatively low VRR, inducing a low processing yield and costs that are too high for the expected selling price. For the process to be more efficient, it was found that the retentate must have a commercial value close to that of the original raw juice. The kinetics of liquefying and concentrating the suspended solid (SS) during enzymatic treatment and microfiltration were monitored for all juices tested. It was shown that, by controlling the VRR, increasing the SS content was possible until it reached the same concentration level found in the raw juice. Under these conditions, the retentate is very similar to the initial juice and can be reintroduced into the pulpy juice processing line. This strategy was carried out on the pulpy juices, following a fully continuous processing with constant feeding and removal of retentate so as to keep the SS content constant in the emerging retentate. During these trials, the permeate flux fluctuated around an average value without showing signs of decreasing. Estimated production costs were also much more competitive. (C) 2001 Elsevier Science Ltd. All rights reserved.