Abstract: The objective of this study was to develop a membrane separation process for the clarification of lychee juice. The effects of trans-membrane pressure (TMP) and axial feed flow rate (Qf) on permeation flux (Qp) under total recycle mode (TRM) during the clarification of lychee juice with ceramic or polyether sulfone membranes were investigated to determine their individual optimal levels. Further, their optimal levels were analyzed when considered concurrently under batch treatment mode. Ceramic membrane was more effective in clarifying lychee juice than polyether sulfone membrane. The optimal operating conditions for clarifying lychee juice with ceramic membrane were determined as 0.3 MPa of TMP and 40 L/min of Qf. Meanwhile, the cause of membrane fouling under batch treatment mode was explored. The R2 obtained from fitting dJ/dt = k(J －Jlim) J2 - n was 0.8812 and 0.8478 for ceramic membrane and 0.9048 for polyether sulfone membrane. Membrane fouling depended on cake filtration (n = 0) for polyether sulfone membrane and dynamic changes between partial pore blocking (n = 1) and cake filtration (n = 0) for ceramic membrane. The dynamic changes of total sugar, total pectin, total protein, antioxidant ability were examined during membrane filtration under batch treatment mode. Ceramic membrane was significantly more effective in maintaining some quality indexes such as total sugar, antioxidant activity and total phenol than polyether sulfone membrane, while no significant difference was observed in other quality indexes.

Key words: ultrafiltration, lychee juice, fouling, quality, mechanism