Immobilization of naringinase on asymmetric organic membranes: Application for debittering of grapefruit juice

An enzymatic membrane reactor (EMR) is assembled for the immobilization of naringinase on a polyethersulfone ultrafiltration membrane, based on fouling-induced method. The effects of molecular weight cut-off, membrane configuration, applied pressure, enzyme concentration and pH are studied in terms of permeate rate, immobilization efficiency, and biocatalytic conversion. The 10 kDa membrane operating in reverse mode, 0.2 MPa, 0.3 gL−1 of enzyme in acetate buffer at pH 5 and cross-linking with 0.25% glutaraldehyde showed the highest naringin conversion (73%). It was determined that the intermediate pore blocking model was the predominant fouling mechanism for the enzymatic immobilization. The EMR was applied for debittering of grapefruit juice, achieving a conversion of naringin below bitterness threshold and maintaining the antioxidant capacity of the juice. Furthermore, the biocatalytic activity of immobilized enzyme was retained at a high level at least during three consecutive reaction runs, with overnight storage at 4 °C after each run. Industrial relevance The potential of membrane technologies in the juice industries is widely recognized today. The development of EMR with naringinase activity is an attractive option for reducing bitterness that could replace current techniques, due to its high specificity and effectiveness, possibility of repeated and continuous use, and in order to retain the properties of juice as much as possible. The research therefore represents an advance in the application of biocatalytic membranes as technological alternative for juice debittering.