Effective clarification of apple juice using membrane filtration without enzyme and pasteurization pretreatment

In this study, the feasibility of clarifying apple juice using membrane filtration without enzyme-hydrolysis and pasteurization pretreatment was investigated extensively. It was found that the enzymatic and pasteurization pretreatment of apple juice had profound influence on the permeate flux and membrane fouling. The enzyme hydrolysis of the apple juice resulted in higher flux. The pasteurization of the apple juice without enzyme pretreatment caused lower flux possibly due to gelatinization at the membrane surface caused by cross-linking between deposited pectin and starch molecules. The permeate flux increased initially with the transmembrane pressure (TMP) and then kept at a plateau as TMP >2.0 bar. Generally, the permeate flux increased with the increase of cross-flow velocity (CFV). The increase of operation temperature from 23 to 50 °C also improved the permeate flux. In the long-term in situ tests without enzymatic pretreatment, the mean flux was higher than 120 l/m2 h (LMH), and high VCF (volume concentration factor, >20) was achieved. The very stable and high flux kept over 20 hours’ industrial simulating tests also indicated that membrane fouling to the filtration performance could be neglected and the major factors influencing permeate flux were the feed concentration and viscosity. The clarified juice has very good quality in NTU, transmittance and color, and no starch, pectin and thermo-acidophilic bacteria (TAB) were detected in the clarified juice. Based on the pilot tests, a new full-scale membrane plant was designed for an apple juice producer and compared with its industrially used tubular membrane system.