Gelation of cowpea proteins by high hydrostatic pressure

Abstract

The gelation of isolated cowpea protein induced by high hydrostatic pressure (HHP, 400 or 600 MPa) was studied in terms of rheological behavior, texture, color, water holding capacity (WHC), scanning electron microscopy and exploration of the interactions that stabilized the gel matrices. Heat-induced gelation was also studied and compared with HHP-induced one. Moreover, absorption and fluorescence spectroscopy under HHP was carried out in order to assess the effect of HHP on cowpea protein structure during treatment and to hypothesize on the gelation mechanism. Both HHP- and heat-induced cowpea gels exhibited an outstandingly high WHC. The rheological behavior of HHP-treated dispersions was compatible with entangled solutions at the lowest protein concentrations (PC, 7.5–10.5% w/w) and with gels at the highest ones (12.0–13.5% w/w). Heating (70 or 90 °C) induced gelation at lower PC. HHP-induced gels were less hard and adhesive than heat-induced ones. At low PC (0.05% w/v), HHP provoked dissociation and exposition of aromatic amino acid residues to water, which was partially reversed during depressurization. These dissociated, unfolded and more hydrophobic polypeptides would establish mainly non-covalent interactions such as hydrophobic and hydrogen bonds, a part of these interactions would occur during depressurization. Heat-induced gels had a higher proportion of strong linkages than HHP-induced ones, which explained the rheological and textural differences. The principle of microscopic order probably prevents rearrangement of reactive sites, leading to HHP-induced gels having fewer interactions than heat-induced ones. HHP-treated CPI could give specific texture characteristics and allow incorporation of thermolabile compounds to food matrices.