Influence of pH on viscoelastic properties of heat-induced gels obtained with a ß-Lactoglobulin fraction isolated from bovine milk whey hydrolysates.

A ß-Lactoglobulin fraction (r-ßLg) was isolated from whey hydrolysates produced with cardosins from Cynara cardunculus. The impact of the hydrolysis process on the r-ßLg structure and the rheological properties of heat-induced gels obtained thereafter were studied at different pH values. Differences were observed between r-ßLg and commercial ß-Lg used as control. Higher values for the fluorescence emission intensity and red shifts of the emission wavelength of r-ßLg suggested changes in its tertiary structure and more solvent-exposed tryptophan residues. Circular dichroism spectra also supported these evidences indicating that hydrolysis yielded an intermediate (non-native) ß-Lg state. The thermal history of r-ßLg through the new adopted conformation improved the microstructure of the gels at acidic pH. So, a new microstructure with better rheological characteristics (higher conformational flexibility and lower rigidity) and greater water holding ability was founded for r-ßLg gel. These results were reflected in the microstructural analysis by scanning electron microscopy.

Characterization of chymotrypsin-ι-carrageenan complex in aqueous solution: a solubility and thermodynamical stability study.

The aim of this study is to report the results of research work on the molecular mechanism of complex formation between chymotrypsin and a negatively charged natural strong polyelectrolyte, ι-carrageenan, using spectroscopy techniques. The carrageenan-chymotrypsin complex showed a maximal non-solubility at pH around 4.50 with a stoichiometric ratio between 8 and 33 g of chymotrypsin per g of carrageenan. These values were depended on the enzyme concentration, pH and ionic strength medium. The insoluble complex was redissolved by modifying the pH and by a NaCl concentration around 0.2 M in agreement with a coulombic mechanism of complex formation. The non-soluble complex formation showed biphasic kinetics. A fast step was carried out around 10 s and a coulombic mechanism takes place, and a slower step of around 120 s, where participate only Van der Waals forces. The enzymatic activity of chymotrypsin was maintained even in the presence of carrageenan (0.005%, w/v).