Effect of polyphosphate binding on the chain dynamic of caseins: investigation by differential scanning calorimetry and thermally stimulated currents

Abstract

Samples of caseins having differentCa contents as used in cheese processing were analysed by techniques using differential scanning calorimetry and thermally stimulated currents (TSC) before and after treatment with Na polyphosphate, a food additive used in the manufacture of processed cheese. These techniques revealed structural changes induced by the salt, and the different types of water molecules associated with the protein are evident. This characterization is in agreement with results obtained by other techniques, particularly X-ray diffraction of proteins. Transmission electron microscopy of the same samples confirmed that the changes observed by TSC were associated with an unravelling of the protein.Polyphosphates have been used for a long time in cheese processing but their exact role is not yet fully understood (Shimp, 1985). For instance, it is not known why the amount of polyphosphates used (from 1 to a few percent) depends on the Ca content of the protein, or how the water-binding ability of the protein is changed after reaction with polyphosphates. Although X-ray studies of crystallized proteins (Blake et al. 1983) revealed that water participates in crystal packing it is not yet known, whether or not such organization exists in lyophilized protein samples similar to those used in cheese processing. Nor is it known what changes result from the addition of polyphosphates. In an attempt to obtain detailed information about the action of added polyphosphates in cheese processing, we have investigated, by differential scanning calorimetry (DSC) and thermally stimulated currents (TSC), samples of caseins before and after their treatment with polyphosphates. MATERIAL AND METHODSSamples of Na caseinate (casein I) and Ca caseinate (casein II) were obtained by spray drying the aqueous solution resulting from neutralizing and precipitating milk curd with NaOH and Ca(0H) 2 respectively. Final pH values were 6-8 for casein I and 6-6 for casein II. Casein I contained 4-7% H 2 O, 1-81% P and 0-026% Ca and casein II 9-9% H 2 O, 1-79% P and 3-44% Ca, expressed as weight percent.Na tripolyphosphate was obtained from Sigma Chemical Co. Reactions of

Solubility and structure of milk powders manufactured with the addition of disodium phosphate and tetrasodium pyrophosphate mixtures

“…In samples containing lower proportions of TSPP (DSP-TSPP mixtures of 0.127:0.073, 0.110:0.90, and 0.105:0.095), the decrease in the ISI compared with control samples could be related to the role of ESs in the destruction of casein micelles [24] and unraveling of the protein chains, which makes more hydrophilic phosphate sites available and promotes casein hydration. [51,52] The latter supposition supports the suggestion that a disruption in protein-protein interactions is required for the protein-water interactions to take place. [20,50,53] Further, according to de Kort et al [16] the decrease in calcium ion activity upon addition of DSP and TSPP results in an increase in the electrostatic repulsion between the casein micelles and an increase in hydration of the micelles.…”

“…[50] Conformational modifications are probably responsible for differences in the binding of water molecules because it is known that the reaction of proteins with phosphate causes variations in their sensitivity to hydration. [51] The results in Table 3 indicate that powders with lower proportions of TSPP (≤47%) had a lower ISI than the control sample, whereas for mixtures with higher proportions of TSPP (≥53%) the ISI was greater than the control. Indeed, the effect observed on insolubility index of powders depended on the proportions of DSP and TSPP in the added mixtures.…”

Physico-chemical characterization of phosphate-added skim milk

“…Secondly, the presence of phosphate can act directly on the hydration of casein molecules. Lamure, Pommert, Klaebe, Lacabanne, and Perie (1988) showed changes in casein conformation and water combination in the presence of polyphosphate.…”