beta-lactoglobulin (beta-1g) was hydrolyzed with three different proteases and subsequently evaluted for its foaming potential. Foam yield stress (tau(0)) was the primary variable of interest. Two heat treatments designed to inactivate the enzymes. 75 degrees C/30 min and 90 degrees C/15 min, were also investigated for their effects on foam tau(0). Adsorption rates and dilatational rheological tests it a model air/water interface aided data interpretation. All unheated hydrolysates improved foam tau(0) as compared to unhydrolyzed beta-lg, with those of pepsin and Alcalase 2.4L (R) being superior to trypsin. Heat inactivation negatively impacted foam tau(0,) although heating at 75 degrees C/30 min better preserved (his parameter than heating at 90 degrees C/15 min. All hydrolysates adsorbed more rapidly at the air/water interface than unhydrolyzed beta-1g as evidenced by their capacity to lower the interfacial tension. A previously observed relationship between interfacial dilatational elasticity (E') and tau(0) was generally confirmed for these hydrolysates. Additionally, the three hydrolysates imparting the highest ro not only had high values of E' (approximately twice that of unhydrolyzed beta-1g). they also had very low phase angles (essentially zero), This highly elastic interfacial state is presumed to improve foam tau(0) indirectly by improving foam stability and directly by imparting resistance to interfacial deformation. (c) 2005 Elsevier Inc. All rights reserved.