Jean-Louis Cuq

Water-holding capacity and characterization of protein interactions in processed cheese

In order to predict the oozing susceptibility of heat-induced milk protein gels such as processed cheeses during storage, ultracentrifugation forces are required to accelerate the expulsion of water from the gel structure. Two predictive methods have been tested. Direct ultracentrifugation of processed cheese was used to study effects of centrifugal compression on the water-holding ability. The water release with optimal parameters (time, temperature and ultracentrifugation force) from a freshly manufactured processed cheese was correlated with visual assessment of oozing after 6 months storage. A second method was based on the susceptibility of gelled proteins to resist the dissociating action of solutions of chemical agents such as SDS, urea, EDTA and 2-mercaptoethanol. Most of the protein sedimented by ultracentrifugation in the presence of SDS represented that still in complexed form. This correlated with optimal water binding by the processed cheese. Response-surface methods, used to optimize the ultracentrifugation variables and the composition of the dissociation solutions, showed that the dissociation test was best with a dispersion of processed cheese in SDS solution (10 g/l) at a ratio of 1:6 (w/v) at 20°C, ultracentrifuged at 86000 g and 20°C for 25 min. Analysis of processed cheese cooked at 115°C and then dissociated in different solutions showed various protein–protein interactions in the gel network, whereas hydrophobic interactions were the most important stabilizers of the protein matrix of cheese cooked at higher temperature.

Packaging films based on myofibrillar proteins : Fabrication, properties and applications

Packaging films based on fish myofibrillar proteins have been developed by two processes. The solvent process based on the casting ofa film-forming solution is affected by protein concentration and pH. The thermoplastic process is based on thermoplastic properties of myofibrillar proteins. The glass transition was observed between 215 and 250°C for the dry protein; addition of water or hydrophilic plasticizers (sucrose and sorbitol) induced large decreases in the glass transition temperature (Tg). Packaging fabrication by a thermomoulding technique was possible at temperature higher than the Tg for a given moisture content. The functional properties of the packaging films were close to those determined for known protein-based films, with tensile strength close to those of low density polyethylene films. Hydration and temperature effects on functional properties could be explained by the glass transition theory.

Influence of chemical agents on casein interactions in dairy products: chemical modification of milk proteins

Abstract Chemical modification of casein micelles by succinylation was investigated in order to assess the role of electrostatic charges in both acid and rennet coagulation, as well as to find a relationship between the chemical modification applied and the ability of milk proteins to coagulate. Succinylation of milk resulted in a delay of gelation and in a decrease in the final firmness of a rennet gel. The resistance of casein micelles to aggregation could be explained by the increase in electrostatic repulsion induced by the introduction of additional negative charges to the proteins. Results showed that the changes in the rheological properties upon rennet coagulation could be related to the microstructural differences observed between the succinylated and the reference milk: so changing the balance of protein charges upon decreasing the pHi increased the coagulation time of acid gels, but might also considerably alter the formation of hydrophobic interactions between succinylated casein micelles during the aggregation phenomena in rennet milk gels.

Edible Wheat Gluten Films: Optimization of the Main Process Variables and Improvement of Water Vapor Barrier Properties by Combining Gluten Proteins with Lipids

An edible wheat gluten film was developed and relationships between film-formation conditions and properties were studied using Response Surface Methodology. pH and ethanol concentration of film-forming solution had strong interactive effects on film water solubility and moisture permeability. Mechanical properties were affected by gluten concentration and pH. Various formulations and methods of fabricating films consisting of gluten and lipids were investigated.