Plant Protein–Polyphenol Conjugates as Antioxidant Pickering Emulsifiers: Ultrasonication-Assisted Stabilization of Shrimp Oil

The study aimed to develop and apply different plant proteins and various polyphenols conjugate as novel antioxidant emulsifiers. Faba bean protein isolate (FBPI) and mung bean protein isolate (MBPI) were conjugated with epigallocatechin gallate (EGCG) or quercetin using free radical grafting method by varying concentrations (50 to 300 mg/g). Antioxidant activities of the conjugates were evaluated, and the selected samples were determined for their structures by spectrofluorometer, FTIR, NMR and gel electrophoresis. FBPI/MBPI conjugated with quercetin (FQ/MQ) at 200 mg/g exhibited superior antioxidant activity compared to EGCG-based conjugates (p<0.05). The conjugation of selected protein and quercetin conjugates was confirmed by decreasing fluorescence intensity as well as changes in FTIR peak intensities and appearance of quercetin-specific NMR signals. Furthermore, protein pattern revealed structural modifications through reduced band intensity and persistence under reducing conditions, confirming covalent/non-covalent interactions in protein-quercetin conjugates. The selected conjugates were then applied to stabilize shrimp oil Pickering emulsions (SOPE) at various levels (0.5-3.0%) with and without ultrasonication. Ultrasonication improved emulsion properties, especially at 0.5% conjugate concentration. SOPE emulsion stabilized with MQ, assisted by ultrasonication, showed higher zeta potential, smaller oil droplets, as well as lower flocculation and coalescence. After 15 days of storage, SOPE containing MQ had significantly lower peroxide and TBARS values than FQ (p<0.05). Confocal microscopy revealed homogeneous oil droplets with slight droplet size increase after 15 days of storage. Overall, polyphenol-protein conjugates, particularly MBPI-quercetin, as effective functional emulsifiers for enhancing food emulsion stability and antioxidant capacity.