Development of lipopeptide surfactants from silk sericin and evaluation of their surface active properties

Abstract

The synthesis of lipopeptides from silk sericin was realized in two steps: enzymatic hydrolysis of protein with Alcalase enzyme and the grafting of lipid chain (C10, C12 or C14) following the Schotten-Baumann reaction. The influence of experimental conditions on the degree of hydrolysis (DH) and the acylation rate (AR) was investigated. Then, equilibrium surface adsorption properties of lipopeptides at air/water interface were studied. The effect of lipopeptide structure, in particular the size of peptide and of the hydrophobic chain, was characterized. Lipopeptides obtained with DH from 20 % to 45 % and AR from 27 % to 41 % were successfully produced. The obtained results demonstrated that sericin peptides have poor amphiphilic properties, whereas lipopeptides efficiently decreased air/water surface tension up to 30.9 mN/m. The surface activity of lipopeptides seem to be closely related to their structure. Sericin lipopeptides show surface properties comparable to those of commercial surfactants, which emphasize the interest of these biomass-derived amphiphilic molecules for potential replacement of petroleum-based surfactants.