Influence of Calcium and Phosphorus, Lactose, and Salt-to-Moisture Ratio on Cheddar Cheese Quality: pH Buffering Properties of Cheese

Abstract

The pH buffering capacity of cheese is an important determinant of cheese pH. However, the effects of different constituents of cheese on its pH buffering capacity have not been fully clarified. The objective of this study was to characterize the chemical species and chemical equilibria that are responsible for the pH buffering properties of cheese. Eight cheeses with 2 levels of Ca and P (0.67 and 0.47% vs. 0.53 and 0.39%, respectively), residual lactose (2.4 vs. 0.78%), and salt-to-moisture ratio (6.4 vs. 4.8%) were manufactured. The pH-titration curves for these cheeses were obtained by titrating cheese:water (1:39 wt/wt) dispersions with 1 N HCl, and backtitrating with 1 N NaOH. To understand the role of different chemical equilibria and the respective chemical species in controlling the pH of cheese, pH buffering was modeled mathematically. The 36 chemical species that were found to be relevant for modeling can be classified as cations (Na+, Ca2+, Mg2+), anions (phosphate, citrate, lactate), protein-bound amino acids with a side-chain pKa in the range of 3 to 9 (glutamate, histidine, serine phosphate, aspartate), metal ion complexes (phosphate, citrate, and lactate complexes of Na+, Ca2+, and Mg2+), and calcium phosphate precipitates. A set of 36 corresponding equations was solved to give the concentrations of all chemical species as a function of pH, allowing the prediction of buffering curves. Changes in the calculated species concentrations allowed the identification of the chemical species and chemical equilibria that dominate the pH buffering properties of cheese in different pH ranges. The model indicates that pH buffering in the pH range from 4.5 to 5.5 is predominantly due to a precipitate of Ca and phosphate, and the protonation equilibrium involving the side chains of protein-bound glutamate. In the literature, the precipitate is often referred to as amorphous colloidal calcium phosphate. A comparison of experimental data and model predictions shows that the buffering properties of the precipitate can be explained, assuming that it consists of hydroxyapatite [Ca5(OH)(PO4)3] or Ca3(PO4)2. The pH buffering in the region from pH 3.5 to 4.5 is due to protonation of side-chain carboxylates of protein-bound glutamate, aspartate, and lactate, in order of decreasing significance. In addition, pH buffering between pH 5 to 8 in the backtitration results from the reprecipitation of calcium and phosphate either as CaHPO4 or Ca4H(PO4)3.

Effect of calcium chelators on physical changes in casein micelles in concentrated micellar casein solutions

“…The added chelator competes with the phosphoserine residues and CCP in the casein micelle for the calcium ions. The chelators have a different affinity for calcium ions, which gives them the ability to release a different amount of CCP from the micelle (De Kort et al, 2009;Mekmene, Le Graet, & Gaucheron, 2009;Turner, Paphazy, Haygarth, & McKelvie, 2002;Upreti, Buhlmann, & Metzger, 2006). Moreover, solubilization of CCP from the micelle depends on the degree of saturation of the calcium complexes formed in the solution (Holt, 1985).…”

Effects of calcium chelating agents on the solubility of milk protein concentrate

“…citrate, phosphate, EDTA) to a milk system, resulting in a decrease in the concentration of free calcium ions and, depending on the extent of chelation, a depletion of colloidal calcium phosphate (CCP; Upreti et al . ; de Kort et al . ; Mekmene et al .…”

Calcium-binding capacity of organic and inorganic ortho- and polyphosphates

“…1a) influences casein micelles by interacting with casein or CCP [4]. Upreti et al [30] and Pyne [22] summarized that CCP is composed of CaHPO 4 , Ca 3 (PO 4 ) 2 , and even larger complexes including those containing crystal water. This indicates that calcium and Na 2 HPO 4 react in a ratio of 1:1 or 3:2 around pH 6.7.…”