Monitoring the effects of divalent ions (Mn+2 and Ca+2) in heat-set whey protein gels

• Type of the divalent ions affects the water uptake behavior of whey protein gels.
• pH and EDTA affected release of cations, which was depicted in relaxation spectra.
• MRI could be used to explore the release of cations from the whey protein gels.

Exploring the effects of cations in whey protein-based gels (WPG) is of importance when these gels are used for controlled release applications in food systems. The objective of this study was to evaluate both water uptake and cation release from heat-set WPGs. Magnetic Resonance Imaging and NMR relaxometry were employed to study the uptake and release. A non-paramagnetic (Ca+2) and a paramagnetic cation (Mn+2) were incorporated into the WPG as model divalent cations. Cylindrical pieces of WPGs with manganese were immersed in water (pH 2.40, 7.00, 10.40) or in EDTA solution whereas WPGs with calcium were immersed in water at pH 2.40. Water uptake by the gels was influenced by both ionic environment and pH. The release of Mn+2 from WPG was enhanced by the presence of EDTA. Relaxation spectra of Mn+2-loaded gels were significantly influenced by pH of the suspending fluid and by the presence of EDTA. Results of relaxometry experiments, obtained with Ca+2-loaded gels immersed in water at pH 2.40, indicated a strong correlation (R2 > 0.99) between relative areas of the proton pools and the amount of calcium released to the medium. Results support the use of MRI and NMR to monitor cation release and water uptake in WPG, non-destructively.