Adsorption of Glycininand β-Conglycinin onSilica and Cellulose: Surface Interactions as a Function of Denaturation,pH, and Electrolytes.

Soybean proteins have found uses in different nonfoodapplicationsdue to their interesting properties. We report on the kinetics andextent of adsorption on silica and cellulose surfaces of glycininand β-conglycinin, the main proteins present in soy. Quartzcrystal microgravimetry (QCM) experiments indicate that soy protein adsorptionis strongly affected by changes in the physicochemical environment.The affinity of glycinin and the mass adsorbed on silica and celluloseincreases (by ca. 13 and 89%, respectively) with solution ionic strength(as it increases from 0 to 100 mM NaCl) due to screening of electrostaticinteractions. In contrast, β-conglycinin adsorbs on the samesubstrates to a lower extent and the addition of electrolyte reducesadsorption (by 25 and 57%, respectively). The addition of 10 mM 2-mercaptoethanol,a denaturing agent, reduces the adsorption of both proteins with asignificant effect for glycinin. This observation is explained bythe cleavage of disulfide bonds which allows unfolding of the moleculesand promotes dissociation into subunits that favors more compact adsorbedlayer structures. In addition, adsorption of glycinin onto cellulosedecreases with lowering the pH from neutral to pH 3 due to dissociationof the macromolecules, resulting in flatter adsorbed layers. The respectiveadsorption isotherms fit a Langmuir model and QCM shifts in energydissipation and frequency reveal multiple-step kinetic processes indicativeof changes in adlayer structure. [ABSTRACT FROM AUTHOR]