impact of soy protein isolate hydrolysis and polysaccharides interactions on kinetic adsorption at air-water interface

K. MARTÍNEZ; C. CARRERA SANCHEZ; J.M.RODRIGUEZ PATINO Y A.M.R.PILOSOF

Buenos Aires

Congreso; XIII Congreso Cytal Congreso Argentino de Ciencia y Tecnología de los Alimentos.”Promoviendo la salud, la calidad y la sustentabilidad; nuevos procesos productos e ingredientes; 2011

Asociación Argentina de Tecnólogos Argentinos

Abstract: The objective of the work was to study the impact of soy protein hydrolysis on kinetic adsorption to the air-water interface and the effect of polysaccharides addition. As starting material a sample of commercial soy protein isolate was used (SP) and hydrolysates were produced by an enzymatic reaction, giving degree of hydrolysis of 2% (H1) and 5.4% (H2) used at 2%wt/wt of concentrations. The polysaccharides (PS) used at 0.25%wt/wt of concentration were a surface active PS: hydroxypropylmethycellulose, (E4M) and a non-surface active one: lamda carrageenan (C). The dynamic surface pressure of films was evaluated with a drop tensiometer at 20ºC, pH 7 and ionic strength 0.05M. To monitor adsorption/penetration/unfolding of adsorbed molecules, the approach proposed by Graham and Phillips was used. Thus, the rate of these processes can be analyzed by a first order equation: ln (180–  / (180- 0) = -Ki where 180, 0 and  are the surface pressures at 180 min of adsorption time, at time = 0, and at any time , respectively, and ki is the first-order rate constant. In practice, a plot of the equation usually yields two or more linear regions. The initial slope is taken to correspond to a first-order rate constant of adsorption (Kp), while the second slope is taken to correspond to a first-order rate constant of rearrangement (Kr), occurring among a more or less constant number of adsorbed molecules. In this contribution, we have determined the kinetic parameters of adsorption to the air-water interface: the penetration (Kp) and rearrangement (Kr) rates of SP, H1, H2 and PS, as well as their mixed systems at 2/0.25%wt/wt respectively. Considerable differences were not found between these two PS studied concerning the Kp to air-water interface at these conditions. In spite of the different surface active nature of the PS, the surface hydrophobicity of proteins seems to control the behavior of the protein-PS interactions. However, when Kr of mixed systems was analyzed, the degree of hydrolysis and PS nature had a huge importance. Hence, it could be observed synergic or antagonic effects on rearrangement rates of biopolymers at liquid interface depending on the degree of hydrolysis of protein analyzed and the type of PS selected in the system.