Effects of mono- and divalent- ions and their strength on foaming properties of infant formula protein model system

Abstract

Metal ions may affect the foaming properties of infant formula products that including milk protein during reconstitution. In this study, an infant formula protein model system (IFPMS) composed of both whey protein and casein was constructed, and the effect of mono (Na+, K+) and divalent (Mg2+, Ca2+) ions and their strength (0–100 mM) on foaming properties was investigated. The mono ions had no significantly impact on foaming capacity (FC), MgCl2 slightly increase FC and reaching a maximum of 116.09 ± 7.46% at 25 mM, whereas CaCl2 significantly decreased FC from 105.78 ± 7.42% to 83.14 ± 6.75% as 0-25 mM (p < 0.05). Foam stability (FS) was significantly improved as all salts above 10 mM (p < 0.05). The dramatically decreased net charge and larger protein aggregates (> 25 mM) of IFPMS with divalent ions indicating their stronger charge-shielding effect, which caused slow adsorption of protein and increased surface tension. Multiple spectral results confirmed that salts enhanced protein interactions via inter-molecular and form a viscoelastic layer to stabilize foam. Absorbed protein and SDS-PAGE analysis revealed that MgCl2 promoted protein adsorption, while CaCl2 reduced casein in the foam phase. Correlation analysis further implied that the FC showed highly significant positive with absorbed protein, solubility, and β-turn (p ≤ 0.01), and FS was significantly correlated with secondary structure and viscosity (p ≤ 0.05). This study may provide useful information for an in-depth understanding of the foaming properties of infant formula.