Deacidification of clarified tropical fruit juices by electrodialysis. Part I. Influence of operating conditions on the process performances

The reduction of acidity of four tropical fruit juices, passion fruit, castilla mulberry, najanrilla and araza, was investigated by using the electrodialysis (ED) process. Two stack configurations using homopolar membranes and three compartments (ED3C), and bipolar membranes and two compartments (EDBM2C), were tested at the laboratory and pre-industrial scale. The ED performances were evaluated as a function of operating conditions such as current density, flow rate, temperature and final pH of the deacidification. The passion fruit, mulberry and naranjilla juices whose acidity is mainly due to the citric acid, had a similar behaviour. A fouling membrane took place in some operating conditions. It is particularly significant with the mulberry juice probably because of its high content in phenolic compounds. Lower ED performances were obtained with the araza juice whose acidity is mainly due to the malic acid. The deacidification was carried out until pH 4, 4.5 or 7.9 with satisfactory results in all cases. Comparing the two ED configurations, ED3C gave better performances than EDBM2C. Nevertheless, the latter configuration allowed the production of the citric or malic acid, and avoided the NaOH consumption induced by ED3C. The use of a pre-industrial pilot with a membrane area 10 times greater and a thickness compartment 13 times lower than the laboratory cell induced a significant decrease in the energy consumption, by 70% and 60%, for ED3C and EDBM2C, respectively.