Behavior of soy globulin films at the air-water interface. Structural and dilatational properties of spread films

RODRIGUEZ PATTINO J.M.; MOLINA ORTIZ S.E.; CARRERA SANCHEZ C; RODRIGUEZ NIÑO M.R.; AÑON, MARÍA CRISTINA

Industrial Engineering Chemistry Research

American Chemical Society

Año: 2003 vol. 42 p. 5011 - 5017

0888-5885

We have studied the structural and surface dilatational characteristics (surface dilatationalmodulus and its elastic and viscous components) of two major fractions of soy globulin from asoy protein isolate, â-conglycinin (a 7S globulin) and glycinin (a 11S globulin)sincluding theeffect of chemical reduction of glycinin with dithiothreitol (DTT)sspread at the air-waterinterface at 20 °C and at pH 2.0, 5.0, and 8.0. The stress response to compression-expansionsinusoidal deformation of the interface in a modified Wilhelmy-type trough with two oscillatingbarriers was measured at a constant amplitude (5% of the initial area) and as a function offrequency (within the range of 1-100 mHz), and superficial pressure. The same experimentaldevice coupled with Brewster angle microscopy makes it possible to determine the structure,morphology, and relative reflectivity of the monolayer. The monolayer structure was moreexpanded on an aqueous subphase at pH 2.0 and the opposite was observed at pH 5.0. Thechemical reduction of glycinin with DTT produced a significant expansion of the monolayerstructure. The monolayer structure determines the surface dilatational characteristics of soyprotein films. It was found that not only is the dilatational modulus determined by theinteractions between spread molecules (which depend on the surface pressure) but also thestructure of the proteins spread on the monolayer plays an important role.