Effect of calcium chelation on the physio-chemical characteristics and rehydration behavior of spray-dried casein-rich powder

Calcium chelators may solve the rehydration difficulty of casein micelle rich powder. However, the thermal effect during spray drying process may modify the calcium-chelated casein structure and affect the powder functionality. This study therefore investigated the effect of calcium chelation and spray drying on casein powder and the corresponding casein structure. Trisodium citrate (TC) was added to 20 % solutions of MCI (micellar casein isolate) powders to bring the TC concentrations up to 10–100 mM before spray drying. The results indicated that TC effectively decreased the particle size of casein clusters and increased zeta potential of casein solutions. Noticeably, high TC (80 & 100 mM) led to high viscosity unsuitable for spray drying. The chelated casein (TCC) powder size decreased significantly from 37.779 ± 1.407 μm to a minimum 12.815 ± 0.660 μm (P < 0.05) compared to MCI. TCC powder with 60 mM TC was spherical and smooth shape, while the others had a concave surface. Within 10–40 mM TC, the α-helices of TCC powders even had higher level of α-helices compared to the control MCI, and had only slight increase of β-turns. The reducing and non-reducing electrophoresis indicated a disulfide crosslinking between κ-casein and β-lg. The wettability of TCC (10–60 mM TC) showed significantly improved wettability reducing contact angle to 40° within 300 s. TCC-40 powders could be fully dissolved within 30 min which demonstrates the improved rehydration of TCC. This study proves that calcium chelated powder owns a relatively good rehydration ability compared to micellar casein powder.