Full scale analysis of apple juice ultrafiltration and optimization of diafiltration

Declining permeate flux and increasing retentate solute concentration during a full scale apple juice ultrafiltration process was investigated. A modified equation and procedure was used for predicting retentate solute concentration (pectin) in the system. Solute concentration in the retentate was indirectly evaluated using the measured values of viscosity, temperature and Brix. The gel-polarization model was then used to analyze the collected data and a good agreement was observed between the experimental data and the model predictions. Fitted model parameters were very close to the published literature values for similar studies in pilot scale systems. According to the model, the optimum concentration for starting the diafiltration operation was 11,913 mg/L. Furthermore, a mathematical analysis was used to launch the diafiltration step based on process time instead of retentate concentration. Solving numerical solution of the governing differential equation by the fourth-order Runge-Kutta method concluded that the suitable time of the diafiltration step was about 7.5 h after having started the ultrafiltration process.