Formulation and characterization of novel acid-induced spray-dried milk protein hydrogel

In this work, a suitable pH and temperature for the fabrication of hydrogels were optimised, and the effects of different pH on the functional characteristics of the hydrogels were studied. To create acid-induced hydrogels, sodium caseinate solutions (10%w/v) were acidified at pH 1.5, 1.75, 2.0, 2.25 and 2.5 using a 1 M HCl solution following heating at 70 °C for 5 min to form solid hydrogels. The hydrogel formed at pH 2.5 exhibited the maximum gel strength, however, reducing pH from 2.5 subsequently decreased the gel strength. The hydrogel was further processed into powder of which functional properties were investigated employing FTIR, DSC, swelling ratio and in-vitro protein digestibility. The swelling ratio, water-holding capacity (WHC) and the in-vitro digestibility of the protein hydrogel developed at pH 1.5 were greater than those of the hydrogels formed at higher pH. The FTIR micrographs confirmed that a slight shift of bonds in the restructured hydrogel was there compared to the non-gelled casein powder (control), nonetheless, non-significant differences were seen between pH 1.5-2.5. DSC results displayed that the high melting endothermic peaks in casein gels might be due to hydrogen bonds developed due to strong interactions with the water molecules during gelation.