Partial calcium depletion during membrane filtration affects gelation of reconstituted milk protein concentrates

Abstract

Milk protein concentrate powders (MPC) with improved rehydration properties are often manufactured using processing steps, such as acidification and high-pressure processing, and with addition of other ingredients, such as sodium chloride, during their production. These steps are known to increase the amount of serum caseins or modify the mineral equilibrium, hence improving solubility of the retentates. The processing functionality of the micelles may be affected. The aim of this study was to investigate the effects of partial acidification by adding glucono-δ-lactone (GDL) to skim milk during membrane filtration on the structural changes of the casein micelles by observing their chymosin-induced coagulation behavior, as such coagulation is affected by both the supramolecular structure of the caseins and calcium equilibrium. Milk protein concentrates were prepared by preacidification with GDL to pH 6 using ultrafiltration (UF) and diafiltration (DF) followed by spray-drying. Reconstituted UF and DF samples (3.2% protein) treated with GDL showed significantly increased amounts of soluble calcium and nonsedimentable caseins compared with their respective controls, as measured by ion chromatography and sodium dodecyl sulfate-PAGE electrophoresis, respectively. The primary phase of chymosin-induced gelation was not significantly different between treatments as measured by the amount of caseino-macropeptide released. The rheological properties of the reconstituted MPC powders were determined immediately after addition of chymosin, both before and after dialysis against skim milk, to ensure similar serum composition for all samples. Reconstituted samples before dialysis showed no gelation (defined as tan δ=1), and after re-equilibration only control UF and DF samples showed gelation. The gelation properties of reconstituted MPC powders were negatively affected by the presence of soluble casein, and positively affected by the amount of both soluble and insoluble calcium present after reconstitution. This work, testing the chymosin-induced gelation behavior of various reconstituted MPC samples, clearly demonstrated that a decrease in pH to 6.0 during membrane filtration affects the integrity of the casein micelles supramolecular structure with important consequences to their processing functionality.

Effects of milk heat treatment and solvent composition on physicochemical and selected functional characteristics of milk protein concentrate

“…The interstudy discrepancy may be related to differences in the concentrations of Ca, P, and [Ca 2+ ] and pH at rennet gelation. The use of cold UF-DF (10°C) by Martin et al (2010), compared with warm UF-DF (50°C) in the current study, is likely to have depleted the concentration of [Ca 2+ ] and CCP in the MPC (Brule and Fauquant, 1981;Law and Leaver, 1998;Eshpari et al, 2015). Hence, Martin et al (2010) found that the addition of CaCl 2 at concentrations of 2 to 3 mM to the aqueous-based MPC restored rennet-induced gelation.…”

“…There are 2 types of HCT versus pH profiles for bovine milk: type A, which is the most common and is characterized by a maximum HCT at pH 6.6 to 6.7 and a minimum HCT at pH 6.8 to 7.0, and type B, for which HCT increases progressively with pH increases in the range of 6.2 to 7.2 (O'Connell and Fox, 2003). Eshpari et al (2015Eshpari et al ( , 2017 altered the solvent composition of protein dispersions (3.2% protein) prepared from standard-or reduced-Ca MPC with protein content ≥80% by overnight dialysis against skim milk at 4°C. The pH of the nondialyzed standard-Ca and reduced-Ca samples was 7.1 and 6.68, respectively, whereas that of the corresponding dialyzed standard-Ca and reduced-Ca samples was 6.65 and 6.65, respectively.…”

Comparative studies of loading lipophilic substances into casein micelles and investigating the influence of whey proteins and heat treatment on loading stability

“…; Dalgleish and Corredig ; Eshpari et al . ). However, earlier analysis (results not shown) revealed that this mainly affects soluble calcium, and thus CM do not disintegrate (Kulozik ).…”

Hardness of high protein nutrition bars based on milk protein concentrates:a review

“…Acidification of skim milk before ultrafiltration, addition of monovalent cations or calcium chelators, and injection with CO2 have been used to reduce the Ca content of MPC. A decrease in the pH of skim milk during UF was reported to affect the integrity and supramolecular structure of casein micelles due to the partial removal of Ca [44,45] and the internal structure of the nondissociated micelles became more homogenous. Replacement ~ 30% of Ca with Na in MPC powder was carried by contacting an aqueous solution of MPC with a strong cation ion exchanger in the sodium form [46].…”