Foaming and interfacial properties of hydrolyzed β-lactoglobulin

β-lactoglobulin (β-lg) was hydrolyzed with three different proteases and subsequently evaluated for its foaming potential. Foam yield stress (τ0) 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 τ0. Adsorption rates and dilatational rheological tests at a model air/water interface aided data interpretation. All unheated hydrolysates improved foam τ0 as compared to unhydrolyzed β-lg, with those of pepsin and Alcalase 2.4L® being superior to trypsin. Heat inactivation negatively impacted foam τ0, 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 τ0 was generally confirmed for these hydrolysates. Additionally, the three hydrolysates imparting the highest τ0 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 τ0 indirectly by improving foam stability and directly by imparting resistance to interfacial deformation.