Foaming and interfacial properties of hydrolyzed β-lactoglobulin

Abstract

β-lactoglobulin ( β-lg) was hydrolyzed with three different proteases and subsequently evaluated for its foaming potential. Foam yield stress ( τ 0 ) was the primary variable of interest. Two heat treatments designed to inactivate the enzymes, 75 °C/30 min and 90 °C/15 min, were also investigated for their effects on foam τ 0 . Adsorption rates and dilatational rheological tests at a model air/water interface aided data interpretation. All unheated hydrolysates improved foam τ 0 as compared to unhydrolyzed β-lg, with those of pepsin and Alcalase 2.4L® being superior to trypsin. Heat inactivation negatively impacted foam τ 0 , although heating at 75 °C/30 min better preserved this parameter than heating at 90 °C/15 min. All hydrolysates adsorbed more rapidly at the air/water interface than unhydrolyzed β-lg, as evidenced by their capacity to lower the interfacial tension. A previously observed relationship between interfacial dilatational elasticity ( E ′ ) and τ 0 was generally confirmed for these hydrolysates. Additionally, the three hydrolysates imparting the highest τ 0 not only had high values of E ′ (approximately twice that of unhydrolyzed β-lg), they also had very low phase angles (essentially zero). This highly elastic interfacial state is presumed to improve foam τ 0 indirectly by improving foam stability and directly by imparting resistance to interfacial deformation.