Influence of chemical agents on interactions in dairy products: Effect of SDS on casein micelles

International audienceThe addition of SDS during skim milk reconstitution is an original approach to study the effect of an ionic amphiphilic molecule on the milk system and particularly on the casein micelle component. SDS-induced changes in casein micelles were investigated by turbidimetry, rheology, scanning electron microscopy (SEM) and biochemical measurements (including soluble proteins analysis). This study shows that casein micelles were able to interact together to form micellar aggregates or milk gel without coagulating agents addition, when milk was reconstituted in the presence of SDS. This micellar aggregation, depending on the SDS concentration, is confirmed by SEM observations showing that the general aspect of casein micelles was affected by SDS treatment. Biochemical analysis indicated that SDS induced micellar casein dissociation. SDS-induced milk gel formation required a defined level of casein dissociation which could be also related to a particular micellar state

Identification of Interactions Among Casein Gels Using Dissociating Chemical Agents

International audienceTo evaluate the nature of the main interactions that are involved in the formation of casein gels made by the acidification or rennet coagulation of milk, we investigated the combined effects of ultracentrifugation and specific dissociating agents on protein solubilization. The method used was based on the ability of gelled proteins to resist the dissociating action of solutions of urea, sodium dodecyl sulfate, or EDTA. Results showed that hydrophobic interactions and calcium bonds were the most important forces involved in the rennet milk gel matrix; hydrophobic, hydrogen, and electrostatic interactions were homogeneously distributed in the gel formed from acidified milk

Effect of Succinylation on the Rennet Coagulation of Milk

International audienceThe effects of succinylation on the rennet coagulation of milk were investigated to find a relationship between the level of chemical modification and the ability of milk protein to coagulate. The strengthening rate and the final firmness of the gel decreased as the extent of succinylation increased, which could be related to the microstructural differences caused by milk succinylation. The kinetics of nonprotein N release were not affected by milk succinylation, but the rennet clotting time increased as the extent of chemical modification increased. These results suggest that milk succinylation affected the secondary or aggregation phase of enzymatic coagulation by increasing the electrostatic repulsions between para-casein micelles and, more indirectly, by dissociating casein from micelles and preventing them from participating in network formation of the gel