Covalent conjugation of Spirulina protein with tannic acid: Characterization of their structure-function attributes
Zahra Najari, Mina Dokouhaki, Pablo Juliano, Benu Adhikari
Abstract
Protein-polyphenol conjugation has gained attention for its potential to improve protein functionality and tailor the structure-function attributes of conjugates for use as ingredients. This study investigated the covalent conjugation of Spirulina protein (SP) with tannic acid (TA) and its impact on the structural and functional attributes of both SP and the resulting SP-TA conjugates. SP was chosen for its sustainable sourcing from algae, while TA was selected for its strong antioxidant properties and ability to undergo covalent conjugation with proteins. Conjugation was carried out under alkaline conditions at pH 9 in the presence of oxygen, using various TA concentrations (0.5–3 mg/mL). Covalent bonding between SP and TA was confirmed through total phenol, free amino and thiol content analysis, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and sodium dodecyl-sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The conjugates had a smaller particle size, higher zeta-potential values, and lower surface hydrophobicity compared to native SP. Their antioxidant activity, assessed through reducing power, DPPH, and ABTS radical scavenging assays, was significantly higher than that of native SP and increased with TA concentration.