Calcium Phosphate In Milk Research Articles

Effect of increasing the colloidal calcium phosphate of milk on the texture and microstructure of yogurt

The effect of increasing the colloidal calcium phosphate (CCP) content on the physical, rheological, and microstructural properties of yogurt was investigated. The CCP content of heated (85°C for 30min) milk was increased by increasing the pH by the addition of alkali (NaOH). Alkalized milk was dialyzed against pasteurized skim milk at approximately 4°C for 72h to attempt to restore the original pH and soluble Ca content. By adjustment of the milk to pH values 7.45, 8.84, 10.06, and 10.73, the CCP content was increased to approximately 107, 116, 123, and 128%, respectively, relative to the concentration in heated milk. During fermentation of milk, the storage modulus (G′) and loss tangent values of yogurts were measured using dynamic oscillatory rheology. Large deformation rheological properties were also measured. The microstructure of yogurt was observed using fluorescence microscopy, and whey separation was determined. Acid-base titration was used to evaluate changes in the CCP content in milk. Total Ca and casein-bound Ca increased with an increase in the pH value of alkalization. During acidification, elevated buffering occurred in milk between pH values 6.7 to 5.2 with an increase in the pH of alkalization. When acidified milk was titrated with alkali, elevated buffering occurred in milk between pH values 5.6 to 6.4 with an increase in the pH of alkalization. The high residual pH of milk after dialysis could be responsible for the decreased contents of soluble Ca in these milks. The pH of gelation was higher in all dialyzed samples compared with the heated control milk, and the gelation pH was higher with an increase in CCP content. The sample with highest CCP content (128%) exhibited gelation at very high pH (6.3), which could be due to alkali-induced CN micellar disruption. The G′ values at pH 4.6 were similar in gels with CCP levels up to 116%; at higher CCP levels, the G′ values at pH 4.6 greatly decreased. Loss tangent values at pH 5.1 were similar in all samples except in gels with a CCP level of 128%. For dialyzed milk, the whey separation levels were similar in gels made from milk with up to 107% CCP but increased at higher CCP levels. Microstructure of yogurt gels made from milk with 100 to 107% CCP was similar but very large clusters were observed in gels made from milk with higher CCP levels. By dialyzing heated milk against pasteurized milk, we may have retained some heat-induced Ca phosphate on micelles that normally dissolves on cooling because, during dialysis, pasteurized milk provided soluble Ca ions to the heated milk system. Yogurt texture was significantly affected by increasing the casein-bound Ca (and total Ca) content of milk as well as by the alkalization procedure involved in that approach.

Impact of consumption of milk and milk products on human health

AbstractThe nutritive value of milk has long been recognised. In the 1920's and 30's several clinical trials explored the influence of a milk supplement on the growth of children. These studies universally showed that milk had a beneficial effect on height gain. The effects of milk on childhood growth were attributed to the impact of the additional dietary calcium on the skeleton, although energy and protein intakes may have been limiting.Contemporary research on the effects of nutrition on growth has the advantage of being able to focus much more specifically on the strength and mineral mass of the skeleton. Curiosity about the relationship between nutrition and skeletal development has arisen because maximising skeletal development in childhood and adolescence is a recognised preventative strategy against osteoporosis. The effect of additional dietary calcium has been explored in a number of clinical trials of children and teenagers using both supplemental calcium and milk and milk products. The studies have generally shown that the rate of skeletal accrual is greater in the supplemented groups, at least in the short-term. Similarly, clinical trials in post-menopausal women show positive effects of calcium in attenuating bone loss and fracture risk.While calcium has been the main nutrient of interest in relation to milk and milk products and their effects on bone growth there is also the possibility that other nutrients which are found in milk may be important. Energy and protein modulate bone growth and micronutrients such as zinc may also have an effect. The form of calcium salt may also be important. It has been proposed that the calcium phosphate in milk may have different mechanistic effects on bone compared to other calcium salts.While these studies show that milk and milk products may decrease the risk of osteoporosis through their effects on growth, recent epidemiological evidence may point to negative influences of childhood growth on later human health. Cancer mortality rates seem to be associated with nutritional conditions which encourage growth in childhood, while the opposite is true for risk of cardiovascular disease.Milk and milk products have also been vilified because of their fat content and the link between fat, particularly saturated fatty acids, and coronary heart disease. The classical diet heart hypothesis centres on the relationship between saturated fatty acids, blood cholesterol and risk of coronary heart disease. This classic diet hypothesis has formed the basis of dietary recommendations to reduce the incidence of coronary heart disease. Dietary change in the direction of reduced consumption of saturated fatty acids, particularly changes in the consumption of milk and milk products has been a bastion of UK dietary recommendations. However, there is debate as to the efficacy of such an approach as a method to reduce deaths from coronary heart disease.Milk protein and lactose may cause adverse reactions in a small proportion of the population. However, exact figures for the prevalence of cow's milk allergy and lactose maldigestion are difficult to estimate.

Interrelationships of the concentrations of some ionic constituents of human milk and comparison with cow and goat milks

1. 1. Milk and milk ultrafiltrate samples from four women ( Homo sapiens) during the first 16 weeks of lactation were analysed for the main salt constituents, protein and lactose and the interrelationships of these constituents were determined. 2. 2. A good positive correlation was observed between ultrafiltrate calcium and citrate concentrations, as previously observed for cow ( Bos taurus) and goat ( Capra hircus) milk but the expected negative correlation of lactose with ultrafiltrate salts was poor. 3. 3. An invariant ion activity product for milk calcium phosphate was found for a dicalcium phosphate stoichiometry but the milk serum was less supersaturated with respect to calcium phosphate and citrate salts than ruminant milks. 4. 4. The observed interrelationships are discussed in relation to the constraints on human milk composition arising from a fixed osmotic pressure, overall charge neutrality and saturation with respect to calcium phosphate.

Changes in Size and Composition of Protein Aggregates on Heating Reconstituted Concentrated Skim Milk at 120oC

ABSTRACTTreatment at 120oC caused initial transfer of protein from the serum and small micelle fraction to the medium‐sized micelle fraction. More extensive heating caused transfer of protein from the medium fraction to the large‐sized micelle fraction, and the serum fraction as 'soluble’casein. Protein composition of large‐sized micelle fraction remained essentially constant, but for the other fractions it changed throughout the heating period. Experiments with heated milks that had been made free of colloidal calcium phosphate (CCP) showed that a proportion of the calcium phosphate in milk, whether indigenous or precipitated by heating, became less soluble. This‘insoluble’calcium phosphate was possibly involved in joining the smaller protein particles into larger‐sized aggregates.

Structural analysis of the environment of calcium ions in crystalline and amorphous calcium phosphates by X-ray absorption spectroscopy and a hypothesis concerning the biological function of the casein micelle

Abstract Determination of the structural environment around calcium ions, using X-ray absorption spectroscopy, in crystalline calcium phosphates is described. The spherically averaged short-range order in an amorphous calcium phosphate can be quantitatively determined using, as a model, the environment of calcium ions in the crystalline calcium phosphate which is closest to it in chemical composition. Structural studies, together with other evidence, suggest that the colloidal calcium phosphate in milk comprises small clusters of Ca 2+ and HPO 4 2− ions in a fairly disordered state. The ion clusters are distributed throughout the micelle and are probably linked through phosphoseryl residues, to the Ca 2+ -sensitive caseins. Calculations indicate that probably about five polypeptide chains interact with a typical ion cluster. The small size of the ion clusters, their amorphous nature and the relative conformational flexibility of the casein proteins suggests a possible biological function for caseins and the casein micelle in the control of calcium phosphate precipitation. During calcium transport by the secretory cells of the mammary epithelium, calcium phosphate is precipitated in the Golgi vesicles. It is suggested that the caseins trap the growth of the precipitate at the nucleation stage, effectively preventing a potentially disastrous first-order phase transition.

Complete nucleotide sequence of the bovine beta-casein gene.

The beta-casein gene is a member of a small gene family encoding the calcium-sensitive caseins, which are specifically synthesized and secreted by the mammary gland during lactation in response to both peptide and steroid hormones. The caseins are involved in the transport of calcium phosphate in milk, which is important for bone development in the infant mammal. We report here the organization and complete DNA sequence of the 8.5 kb long bovine beta-casein gene. Comparison with the rat beta-casein gene reveals that the exons of both genes correspond exactly. The 5' flanking sequences of all Ca-sensitive casein genes are conserved within the proximal 200 bp and contain several elements that probably function as cis-acting regulatory elements, including an octamer-like motif, and SV40-type core enhancer and a sequence that appears to be common to all lactoprotein genes. The latter sequence is flanked on either side by 12 bp direct repeats. These direct repeats are themselves each part of sequences that display two-fold symmetry. The first 30 nucleotides of the 3' flanking regions in the bovine and rat beta-caseins are well conserved, indicating that they are likely to be involved in the mechanism of 3' end processing of the primary transcript.

Comparison of the structure of micellar calcium phosphate in milk from six species by extended X-ray absorption fine structure spectroscopy

SUMMARYExtended X-ray absorption fine structure spectra, above the Ca K absorption edge, were recorded from lyophilized casein micelles obtained from the milk of cow, pig, goat, rabbit and rat. A spectrum was also obtained from the calcium phosphate prepared from the casein micelles of human milk. Comparison of these spectra showed that the short-range environment of calcium in the micellar calcium phosphate was the same in all six species. Furthermore, these spectra closely resembled that of brushite (CaHP04. 2H20). However, X-ray diffraction showed no evidence for an extensive crystal lattice in micellar calcium phosphate.

Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems

The present studies show that the colloidal calcium phosphate of cow's milk has a (Ca + Mg)/P i ratio of 1.67 (± 0.10; n = 22) and contains citrate, Mg and Zn at molar ratios to Ca averaging 0.05, 0.03 and 0.003, respectively. The composition of the natural colloidal phosphate of milk is similar to the precipitates formed by neutralization of ultrafiltrates obtained from acidified milks, and to that of the calcium phosphate-enriched fraction produced by extensive enzymic hydrolysis of the casein micelles in milk. Examination by electron microscopy of these artificial preparations of milk calcium phosphate revealed in both a very fine and uniform substructure which consisted of granules having an average, true diameter of approx. 2.5 nm. The size and shape of these tiny granules closely resemble the morphologies reported for the colloidal phosphate particles in native casein micelles, as well as for the subunits of amorphous calcium phosphate observed during calcification in other biological systems such as mitochondria and bone.

Influence of some polyvalent organic acids and salts on the colloidal stability of milk

Fifteen polyvalent organic salts and acids increased, some very markedly, the heat stability of milk progressively with increasing concentration; acetate and mesaconic acid had no effect, and maleate caused destabilization. Citrate, oxalate and EDTA markedly reduced the [Ca+] in the milk and increased its ethanol stability by shifting the ethanol/pH profile to lower pH values. These additives ≥ 20 mmol/l prevented the coagulation of milk by rennet, but the other additives caused only slight increases in RCT.Citrate, EDTA and oxalate disrupted casein micelles and would therefore not be suitable additives: however, the other acids and salts did not alter the appearance of the milk and might be recommended as suitable additives to improve the heat stability. In terms of the response to the level of Ca2+ and colloidal calcium phosphate in milk, there appeared to be a correlation between ethanol stability and rennet coagulation time.

Structure of bovine milk calcium phosphate determined by X-ray absorption spectroscopy.

Calcium in cow's milk is mainly in the form of calcium phosphate-phosphoprotein complexes known as casein micelles. These micelles, in contrast to other phosphoprotein complexes in bone and other tissues, can be readily isolated and studied, but conventional techniques have given ambiguous and conflicting evidence on the structure of milk calcium phosphate. Extended X-ray absorption fine structure and near-edge structure measurements at the newly commissioned Synchrotron Radiation Source at Daresbury indicate that it closely resembles brushite, CaHPO4 X 2H2O. This result, and chemical analysis, requires that phosphate groups from the matrix phosphoproteins be incorporated in the brushite lattice, probably in the surface, suggesting that these organic phosphate groups act as heterogeneous nucleation sites for phase separation of the calcium phosphate from solution.

Inorganic constituents of milk. III. The colloidal calcium phosphate of cow's milk.

Experiments involving the depletion of milk calcium phosphate (MCP) with EDTA have shown that it has a Ca to phosphate ratio of 1.61 +/- 0.04, close to that of dental enamel. The calcium phosphate also contains small amounts of citrate (citrate/Pi = 0.097 +/- 0.011 and Mg (Mg/Pi = 0.044 +/- 0.011). These experiments and model calculations indicate that the Ca binding capacity of casein is not reduced by mineralization with calcium phosphate and hence that ion binding sites and nucleation sites are distinct, or nearly so. Calculations of the ionic equilibria in the aqueous phase of milk show that there is an invariant ion activity product for a molecular formula close to that of dicalcium phosphate. It is suggested that MCP is a mixture of salts, with dicalcium phosphate a precursor of more basic salts such as octacalcium phosphate and hydroxyapatite.

Some Principles Determining Salt Composition and Partitioning of Ions in Milk

Secretion of milk salts via the transcellular and paracellular routes is subject to the constraint that the fluid remains isosmotic with blood. This principle has been applied in the understanding of correlations between concentrations of monovalent ions and lactose. Concentrations of multivalent ions are the result of complex equilibria involving both constituents of the aqueous phase and milk proteins and calcium phosphate in the colloidal phase. All of these concentrations can be calculated with a model of the ion equilibria and an effective solubility product for milk calcium phosphate. The calcium chelating agents — mainly citrate, casein, and orthophosphate — give rise to an increased accumulation of calcium for a given free calcium ion concentration in Golgi vesicles. The latter is probably established by an active transport mechanism, and considerations such as these are required for an understanding of multivalent ion concentrations in milk.

The colloidal phosphate of milk: II. Influence of citrate

SummaryA new method for determining the composition of the colloidal phosphate of milk has been developed, based on analysis of milk free from colloidal phosphate. Preparation of this material is described.The results suggest that the so-called colloidal calcium phosphate of milk should be more properly described as a colloidal phosphate—citrate.This colloidal phosphate—citrate shows considerable analytical resemblance to the precipitate formed on neutralizing acidified milk serum. Both can be represented approximately by the empirical formula of a hypothetical citrate apatite.

Effect of Pasteurization and Cool-Aging on the Salt Balance in Milk

Summary The effects of pasteurization and cool-aging on the distribution of calcium, magnesium, phosphorus, and citric acid in milk into curd and whey were studied by analyzing these constituents in rennet whey from milk after the appropriate treatments. Statistical analysis of the data from ten bulk-milk samples revealed that the differences were not significant, except with respect to magnesium in curd from cool-aged milk. These variations, however, did not reflect any significant change in the Ca:P ratios in the curd. The results were not in harmony with the observations on pure salt solution under similar conditions, and the variations in the behavior of milk are considered partly due to the colloidal systems present in milk. The importance of considering magnesium and citric acid simultaneously is pointed out in any attempt to explain the ionic equilibria regarding calcium phosphate in milk.

Rennet hysteresis and the calcium phosphate of milk

Rennet hysteresis and the calcium phosphate of milk

134. The Titration of Milk and Whey as a Means of estimating the Colloidal Calcium Phosphate of Milk

1. The titration method for the estimation of colloidal tricalcium phosphate in milk was found to agree closely with the determination of total colloidal inorganic P2O5.2. The method was used to study the solution of tricalcium phosphate in milks of rising acidities.3. Close agreement was obtained between the actual increase in total P2O5 in the wheys of souring samples and that calculated from the disappearance of tricalcium phosphate as found by the titration method.4. The discrepancy between the actual increase in whey calcium in such cases and that calculated from the titration figures was attributed to the solution of calcium from the calcium salt of caseinogen. From figures so obtained it would appear that colloidal calcium phosphate dissolves with greater ease in milk than the calcium of the protein salt.5. A linear relationship was found to exist between the ordinary titration value of milk and the three other values used in this estimation, and also between the curd acidity and milk acidity.6. Average figures are given for the tricalcium phosphate content of the samples studied and for the various titration factors.

The Solubility of Calcium Phosphate in Fresh Milk

Summary A calculation has been made of the calcium ion concentration of normal fresh milk. This calculation is based on recent experimental results bearing on the mutual effects of hydrogen, calcium, phosphate and citrate ions on one another. A calculation of the ion product (Ca ++ )×(HPO 4 = ) in normal fresh milk gives a value less than that of the corresponding solubility product. Experimental evidence as to the validity of the method of calculation is offered in the form of an experiment in which the precipitation of calcium phosphate was prevented by the presence of citrate. It is concluded that the solubility of calcium phosphate in milk is affected by the amount of citrates present and that this effect is probably specific.