Characterization of norbixin and evaluation of its mobility through rennet-induced micellar casein concentrate gels as influenced by an electrical field

In this study, application of an electrical field to facilitate the migration of norbixin molecules through rennet-induced micellar casein concentrate (MCC) and agar gels was evaluated. To determine the effect of selected parameters on norbixin penetration through the renneted casein gels, MCC, as a curd-like structure, was used to simplify the study of the process and evaluate the impact of each parameter on the migration of norbixin molecules separately. The physicochemical properties of norbixin solutions were characterized, followed by evaluation of the effects of changing gel composition on colorant mobility—influenced by an electrical field. Multi-angle dynamic light scattering enabled size measurement of norbixin solutions. A strong negative charge (−53.4 to −73.4 mV) was observed at all pH values examined. Localization of norbixin molecules within the aqueous phase was shown by confocal laser scanning microscopy. Norbixin solutions, characterized by LUMiSizer and light microscopy, showed the formation of aggregates (30–50 μm) in the presence of CaC1₂. Reducing pH and increasing calcium content considerably decreased norbixin penetration through the gels. The penetration rate of norbixin was considerably reduced (~ 60%) in the presence of 2% of calcium chloride. By reducing the pH from 6.58 to 5.37 and 6.60 to 5.30, the penetration rate of color through the gels containing 7.5 and 15% protein was reduced by ~90 and 80%, respectively. However, as salt concentrations increased (0% to 4%), the penetration rate of the colorant through MCC gels of 15% protein increased by 60%. Overall, this work shows that applying an electrical field is a promising approach which may considerably increase the migration rate of colorant through rennet-induced casein gels.