Modification of the interfacial properties of sodium caseinate using a commercial peptidase preparation from Geobacillus stearothermophilus

Abstract

Sodium caseinate was hydrolyzed with the commercial enzyme preparation Sternzym BP 25201, containing a thermolysin-like peptidase from Geobacillus stearothermophilus as the only peptidase. The hydrolysis was carried out at 65 °C with an enzyme activity of 1 nkat mL−1 or 15 nkat mL−1, leading to various degrees of hydrolysis (DH) ranging between 0.1 and 8.5%. The hydrolysates obtained were analyzed in a multi-scale approach, covering the hydrolysate properties (viscosity, hydrophobicity, peptide composition) and their interaction at oil–water (emulsion) and air–water (foam) interphases. The viscosity and surface hydrophobicity generally decreased with an increasing DH. Longer, more hydrophobic peptides, which self-assembled into network-like supramolecular particles, were detected up to a DH of 2.2%. Compared to untreated sodium caseinate, these structures could increase the half-life of emulsions (+400%) and foams (+31%). This was most probably caused by an increase in particle size (45.2-fold). By contrast, a higher DH led to a less hydrophobic product and smaller, spherical-shaped supramolecular structures. Foams and emulsions prepared with those hydrolysates were not stable and phase separated within minutes (for example, emulsion half-life = 5 min; foam half-life = 4.6 min at DH of 8.5%).