Non-contaminative MIL-53(Fe)-anchored ultrafiltration membrane for apple juice sterilization: Anti-biofouling performance and mechanism

Residual Alicyclobacillus acidoterrestris severely impacts juice quality. Conventional thermal treatments fail to completely eliminate bacteria and simultaneously cause the loss of heat-sensitive components. Ultrafiltration (UF) has been a nonthermal alternative to conventional thermal process for the sterilization of apple juice. However, membrane fouling, particularly biofouling is an obstacle for deployment of UF in food processing. In order to tackle the challenging issue of membrane biofouling while ensuring food safety, functionalized UF membrane was developed by multi-stage modifications including metal chelator coating and chlorogenic acid-encapsulated MIL-53(Fe) microparticle grafting. The engineered membrane was applied for cold sterilization of apple juice to remove Alicyclobacillus acidoterrestris. Results showed that (i) the engineered membrane could release chlorogenic acid in response to pH stimulation, (ii) the steady state flux of engineered membrane was maintained higher than the pristine membrane after filtration with contaminated apple juice. Only 4.9 % viable bacteria were observed on the membrane surface, (iii) the antibacterial mechanism of engineered membrane was mainly due to the disruption of cellular structural integrity and enhanced permeability of cell membranes, which caused the damage to A. acidoterrestris cell, (iv) after filtration, the Fe³⁺ concentration in the permeate solution was almost undetectable. The engineered membrane can simultaneously exclude and inactivate A. acidoterrestris in apple juice, while demonstrating excellent anti-adhesion and anti-biofouling properties. Furthermore, the engineered membrane complies with food safety requirements, which verifies that this metal-organic framework modification method has the potential for practical application in food processing.