Ultrasound-assisted conjugation of <i>Moringa</i> proteins with gallic acid: characterisation of structural and techno-functional properties

Abstract In this study, ultrasound-assisted covalent binding method, free radical-induced method, was used to prepare Moringa protein isolate (MPI) – gallic acid conjugates (MPI-GAC) to examine the improvement of the sonication application. Additionally, the influence of polyphenol conjugation on functional and structural attributes of MPI was assessed thru spectral analysis, scanning electron microscopy, antioxidant activity, emulsification, foaming, and water and oil holding properties. The enhanced value of grafted polyphenol species was observed after introducing ultrasound treatment during free radical mediation process. The structural changes in protein by gallic acid conjugation were confirmed by using FT-IR which illustrated the modification in MPI-GAC with modified peak width of the amide-I band. Scanning electron microscopy also showed a significant difference in the structure of MPI and MPI-GAC. The grafting of gallic acid onto MPI directed under ultrasound-assisted conditions conferred distinctive functional characteristics, containing elevated emulsification capacity (51.4 mg mL−1) along with enhanced water and oil holding capacity by 2.07 and 5.11 g g−1, respectively. Furthermore, conjugation also increased the protein solubility 89.3–97.6% and significant trend (68.04–88.06%) of antioxidant capacity was observed by increasing the concentration. The findings of this research work offer new insights on the effective fabrication of MPI-GAC with multifaceted functionalities, thus broadening the scope and possibilities of high-value Moringa seed protein.