Tensoactive species obtained by papain hydrolysis of soy protein were characterized structurally and physicochemically, and their foam-forming and -stabilizing capacity studied. Protein structural changes upon reaction ending were correlated with functional and interfacial properties and with the behaviour thereof with varying hydrolysis degree. Two different means of halting hydrolysis -pH reduction (pH=2) and quick freezing (-18ºC), respectively- were studied. Distinct structural changes and associated functional properties were found according to reaction ending conditions. No improvement of foaming properties was found for partially-hydrolyzed isolates subject to freezing at reaction ending - with respect to the starting unhydrolyzed soy protein isolate. In contrast, pH treatment as a means of halting hydrolysis led to a significant enhancement of the foaming properties of soybean protein hydrolysates consistently for all studied hydrolysis degrees (0%, 1.8%, 2.5% and 6%).Centro de Investigación y Desarrollo en Criotecnología de Alimentos