Milk protein suspensions enriched with three essential minerals: Physicochemical characterization and aggregation induced by a novel enzymatic pool

Abstract

Structural changes of casein micelles and their aggregation induced by a novel enzymatic pool isolated from Bacillus spp. in the presence of calcium, magnesium or zinc were investigated. The effect of cations on milk protein structure was studied using fluorescence and dynamic light scattering. In the presence of cations, milk protein structure rearrangements and larger casein micelle size were observed. The interaction of milk proteins with zinc appears to be of a different nature than that with calcium or magnesium. Under the experimental conditions assayed, the affinity of each cation for some groups present in milk proteins seems to play an important role, besides electrostatic interaction. On the other hand, the lowest aggregation times were achieved at the highest calcium and zinc concentrations (15 mM and 0.25 mM, respectively). The study found that the faster the aggregation of casein micelles, the less compact the gel matrix obtained. Cation concentrations affected milk protein aggregation kinetics and the structure of the aggregates formed.

Mineral fortification modifies physical and microstructural characteristics of milk gels coagulated by a bacterial enzymatic pool

“…The dispersion was stirred for about 1 h at 25°C before each experiment to allow equilibration. Subsequent dilutions, for the fortification using minerals, were carried out using 10 mM Tris-HCl buffer pH 7.4 (Sigma-Aldrich Co., St Louis, USA) [9].…”

“…Specific affinity of each cation for some groups in milk proteins could be playing a more important role than plain electrostatic interaction, i.e. the ionic strength effect [9,28].…”

“…At pH 7.4, caseins have net negative charge, which is screened by the added cations leading to bigger casein micelles [9]. EPP7-induced coagulation of milk suspensions in the presence of high concentration of divalent cations would lead to more compact milk gels with smaller PD.…”

“…Secondly, what mineral salt is best to use and how much of it is necessary to add to ensure enough concentration in the food product. As this second issue has been previously discussed [9], now we focus on the influence of the selected mineral salts on the optical and mechanical properties of EPP7-induced milk gels. To achieve this, experiments of confocal scanning laser microscopy (CSLM), penetrometry and color analysis were carried out.…”

“…P7 (EPP7) has been proposed as milk coagulant. EPP7 consist mainly of serine proteases and its optimal temperature and pH for milk protein aggregation are 44 °C and 7.4, respectively [8,9]. In a previous work, milk protein aggregation by EPP7 in the presence of nutritionally essential minerals was characterized [9].…”