Stability of casein micelles cross-linked with genipin: a physicochemical study as a function of pH

Chemical or enzymatic cross-linking of casein micelles (CMs) increases their stability against dissociating agents. In this paper, a comparative study of stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a function of pH is described. Stability to temperature and ethanol were investigated in the pH range 2.0-7.0. The size and the charge ($\zeta$-potential) of the particles were determined by dynamic light scattering. Native CMs precipitated below pH 5.5, CMs-GP precipitated from pH 3.5 to 4.5, whereas no precipitation was observed at pH 2.0-3.0 or pH 4.5-7.0. The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability against heat and ethanol was observed for CMs-GP at pH 2, where visible coagulation was determined only after 800 s at 140 $^\circ$C or 87.5% (v/v) of ethanol. These results confirmed the hypothesis that cross-linking by GP increased the stability of CMs.Comment: 5 pages, 2 figures, International Dairy Journal, 201

Physico-chemical stability of casein micelles cross-linked by transglutaminase as a function of acidic pH

Casein micelles (CMs) can be used as nanocarriers in food and pharmaceutical applications, but can be destructured by changes in the physicochemical environment. Enzymatic crosslinking with transglutaminase (Tgase) is a possibility to stabilize CMs. The objective of this paper was to evaluate the stability of native CMs and CMs cross-linked by Tgase (CMs-Tgase) as a function of pH, in the presence of following destabilizing agents: urea, sodium citrate, high temperature and ethanol. Suspensions of native and CMs-Tgase were prepared at 27.5 g/L in 25 mM HEPES buffer with 2 mM CaCl2 at pH 7.10 The CMs' size and zeta-potential were determined by dynamic light scattering. Native CMs precipitated below pH of 5.5. CMs-Tgase precipitated between pH 4.5 and pH 3.5 but was stable in the pH range of 7.0-4.5 and between pH 2.0 and 3.0. Isoelectric points of CMs and CMs-Tgase were determined as been 4.6 and 4.1, respectively. CMs-Tgase were stable at pH 2.0, in the presence of 100 mM of sodium citrate, 8 M urea, 99.5% (v/v) of ethanol and presented an heat coagulation time higher than 500 s at 140 degrees C. These results were interpreted as a consequence of the formation of internal covalent bounds between casein chains, and to a covalent attachment of the kappa-caseins onto the surface of the CMs. In light of these results, it is possible to investigate CMs-Tgase as stable food-grade nanocarriers, whose characteristics can be modulated according to the chemical nature of the target biomolecule19CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGnão temnão temnão te

Effect of Moderate Electric Fields on the Physical and Chemical Characteristics of Cheese Emulsions

Cheese powder is a multifunctional ingredient that is produced by spray drying a hot cheese emulsion called cheese feed. Feed stability is achieved by manipulating calcium equilibrium using emulsifying salts. However, the increased demand for ‘green’ products created a need for alternative production methods. Therefore, this study investigated the impact of ohmic heating (OH) on Cheddar cheese, mineral balance, and the resulting cheese feed characteristics compared with a conventional method. A full factorial design was implemented to determine the optimal OH parameters for calcium solubilization. Electric field exposure and temperature had a positive correlation with mineral solubilization, where temperature had the greatest impact. Structural differences in pre-treated cheeses (TC) were analyzed using thermorheological and microscopic techniques. Obtained feeds were analyzed for particle size, stability, and viscosity. OH-treatment caused a weaker cheese structure, indicating the potential removal of calcium phosphate complexes. Lower component retention of OH_TC was attributed to the electroporation effect of OH treatment. Microscopic images revealed structural changes, with OH_TC displaying a more porous structure. Depending on the pre-treatment method, component recovery, viscosity, particle size distribution, and colloidal stability of the obtained feeds showed differences. Our findings show the potential of OH in mineral solubilization; however, further improvements are needed for industrial application