Temperature effects on calcium binding to caseins

Effect of lactation on the distribution of mineral elements in goat milk

The distribution of mineral elements in milk is crucial for their absorption and utilization, however, there has been limited attention given to the status of mineral elements in goat milk. In this study, goat milk was collected at 4 lactation periods (1-3, 90, 150, 240 d) and separated into 4 fractions (fat, casein, whey, and aqueous phase). The concentrations of Mg, Ca, Na, K, Zn, Fe, Cu, Mn, Co, Ni, Mo, and Cr in 4 fractions were analyzed using an inductively coupled plasma emission spectrometer. Our findings reveal that Ca, Zn, Fe, Cu, Mn, and Cr exhibit the highest levels in casein, while Mo demonstrates the highest content in whey. Additionally, Mg, Na, K, and Ni display the highest concentrations in the aqueous phase. Specifically, the contents of Ca, Cu and Fe in casein decrease from 1-3 to 150 d of lactation but increase from 150 to 240 d of lactation. Furthermore, the content of Mg in the aqueous phase decreases from 1-3 to 90 d of lactation but increases from 90 to 240 d of lactation. The content of Na and K in the aqueous phase decreases from 1-3 to 150 d of lactation. Notably, the content of Mo in whey increases from 1-3 to 150 d of lactation and decreases from 150 to 240 d. Our research contributes to the advancement of understanding the bioavailability of mineral elements in goat milk.

Influence of pH on Heat-Induced Changes in Skim Milk Containing Various Levels of Micellar Calcium Phosphate

The present study investigated the effect of micellar calcium phosphate (MCP) content and pH of skim milk on heat-induced changes in skim milk. Four MCP-adjusted samples, ranging from 67 to 113% of the original MCP content, were heated (90 °C for 10 min) at different pH values (6.3, 6.6, 6.9, and 7.2), followed by determining changes in particle size, turbidity, protein distribution, and structure. The results demonstrate a strong effect of MCP level and pH on heat-induced changes in milk, with the MCP67 samples revealing the greatest thermal stability. Specifically, decreasing MCP content by 33% (MCP67) led to a smaller increase in non-sedimentable κ-casein and a lower decrease in αs2-casein concentrations after heating compared to other samples. Lower MCP content resulted in a moderate rise in the average particle size and turbidity, along with lower loading of β-turn structural component after heating at low pH (pH 6.3). Notably, MCP113 exhibited instability upon heating, with increased particle size, turbidity, and a significant decrease in non-sedimentable αs2-casein concentration, along with a slight increase in non-sedimentable κ-casein concentration. The FTIR results also revealed higher loading of intermolecular β-sheet, β-turn, and random coil structures, as well as lower loading of α-helix and β-sheet structures in MCP-enhanced skim milk samples. This suggests significant changes in the secondary structure of milk protein and greater formation of larger aggregates.

Dietary calcium intake and the risk of stroke: Meta-analysis of cohort studies

BACKGROUND AND AIMS

Prospective cohorts are inconsistent regarding the association between dietary calcium intake and the risk of stroke. The aim was to perform a meta-analysis to determine whether an association exists between them in cohort studies.

METHODS AND RESULTS

Relevant studies were identified by searching PubMed, EMBASE and Web of Science databases that published before December 2022. Prospective cohort studies that provided relative risk (RR) estimates with 95% confidence intervals (CIs) for the association were included. Study-specific risk estimates were combined by using a random effects model. Eighteen prospective studies, including 19,557 stroke cases among 882,181 participants, were pooled in the meta-analysis. We observed a nonlinear association between calcium intake and risk of stroke (P_nonlinearity < 0.003). Compared with the lowest value of zero assumed as the reference, the RRs (95% CI) of stroke across levels of calcium intake were 0.95 (0.92, 0.98) for 200 mg/day, 0.94 (0.90, 0.98) for 300 mg/day, 0.95 (0.90, 0.99) for 500 mg/day, 0.98 (0.93, 1.03) for 700 mg/day, and 1.04 (0.97, 1.11) for 1000 mg/day. The stratified analyses by geographic region showed nonlinear associations and indicated that the protective effect was observed in Asian countries (P_nonlinearity = 0.001) but not in non-Asian regions (P_nonlinearity = 0.047).

CONCLUSION

This meta-analysis suggests that dietary calcium intake might play an effective role in the prevention of stroke, especially in Asian countries. Future research among Asia population should attempt to establish whether this association is causal.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022357710.

Comment on "Deciphering calcium-binding behaviors of casein phosphopeptides by experimental approaches and molecular simulation" by M. Luo, J. Xiao, S. Sun, F. Cui, G. Liu, W. Li, Y. Li and Y. Cao, Food Funct., 2020, , 5284

But this system is not as simple as depicted since co-precipitation of all three reagents occurs when CPP is included.