Title : Concentration of phenolic compounds from orange pomace: Investigation of graphene oxide modified membranes to fouling mitigation
Abstract:
The production of fruit juices results in large quantities of by-products rich in antioxidant substances. An example of this is citrus fruit residue, which contains high levels of phenolic compounds and flavonoids, which can reduce the risk of several diseases. Membrane separation processes are environmentally friendly and operate at mild temperatures, making them attractive for the concentration and purification of plant extracts. Thus, the aim of the present study was to modify the membrane surface with sulfonic groups, polyethyleneimine, and graphene oxide nanoparticles functionalized with tannic acid to concentrate phenolic compounds from orange pomace extract. Polyethersulfone microfiltration membranes (0.45μm) were modified using the coating technique in which the modifying solutions were filtered without pressure for 20 min as follows: 25 ml of 10% (v/v) sulfuric acid solution, aqueous solution containing 12.4 mg of PEI, and finally, suspension containing 1.12 mg of graphene oxide and 4.50 mg of tannic acid. After filtration of the orange residue extract, the fouling rates for the control and modified membrane were 87.71 and 70.69%, respectively, indicating the anti-fouling action of tannic acid and graphene in membranes. The morphologies of the membranes evaluated by SEM indicated pores across the entire surface of the control membrane. After modification, a rough surface was observed, which can be attributed to the functionalization of graphene oxide using tannic acid. The content of phenolic compounds in the permeates obtained after filtration using the control membrane and the modified membrane was 2.70 ±0.01 mg EAG/g and 0.90 ±0.01 mg EAG/g, respectively. These values indicate that the modified membrane retained approximately 78% of the phenolic compounds. The bioactive compounds present in the orange pomace extract and permeates were identified by UPLC-MS/MS: hesperidin (m/z 611.19), naringin (m/z 581.19), (±)-naringenin (m/ z 273.07), hesperetin (m/z 303.09), p-Coumaric acid (m/z 165.05). Thus, filtration through modified membranes is a promising alternative for the concentration and purification of food extracts.
