Immobilization of ß-galactosidase by complexation: Effect of interaction on the properties of the enzyme.

In the present work, we aimed to explore the molecular binding between alginate and ß-galactosidase, as well as the effect of this interaction on the activity retention, thermal stability, and kinetic properties of the enzyme. The impact of pH and enzyme/alginate ratio on physicochemical properties (turbidity, morphology, particle size distribution, ζ-potential, FTIR, and isothermal titration calorimetry) was also evaluated. The ratio of biopolymers and pH of the system directly affected the critical pH of complex formation; however, a low alginate concentration (0.1 wt%) could achieve an electrical charge equivalence at pH 3.4 with 93.72% of yield. The binding between ß-galactosidase and alginate was an equilibrium between enthalpic and entropic contributions, which promoted changes in the structure of the enzyme. Nevertheless, this conformational modification was reversible after the dissociation of the complex, which allowed the enzyme to regain its activity. These findings will likely broaden functional applications of enzyme immobilization.

Interpolymer complexation of egg white proteins and carrageenan: Phase behavior, thermodynamics and rheological properties.

The complexation between lysozyme/carrageenan and ovalbumin/carrageenan was studied in situ using acidification. The complexes were analyzed in solutions with different NaCl concentrations and different protein/polysaccharide ratios. As the protein/polysaccharide ratio increased from 1:1 to 10:1, critical structure forming events (i.e., those associated with soluble, insoluble and large insoluble complexes) shifted to higher pH values for ovalbumin/carrageenan followed by decrease of G' values at ratios of 5:1 and 10:1. The increase in the ratio of lysozyme/carrageenan complexes suppressed the critical pH transition points that led to the formation of large insoluble complexes from pH 12.0 until 1.0, and the values of G' increased simultaneously, reaching the highest value at a ratio of 10:1. Addition of salt to the ovalbumin/carrageenan and lysozyme/carrageenan mixtures suppressed the electrostatic interaction between proteins and carrageenan at lower pH values and the critical pH transitions points, whereas at a ratio of 3:1 with a 0.01 M concentration, the coacervate yield of the complex reached 79.6% ±â€¯0.6 and 93.7% ±â€¯4.8 for the ovalbumin and lysozyme complexes, respectively. The rheological data associated with microscopy images show that interpolymer complexes with heterogeneous structures were formed for both complexes, and we suggest that complexes have a great potential to improve or extend the texture, mechanical stability, consistency, and taste of food products.