Determination of the critical aggregation concentration in water of Gum Arabic functionalized with curcumin oxidation products by micro-scale thermophoresis approach.

Gum Arabic underwent enzymatic modification with curcumin oxidation products, prompting self-assembly in water at lower concentrations than native gum Arabic, which was fully soluble. The resulting particles displayed a narrow size distribution, suggestive of a micellization mechanism akin to Critical Micellization Concentration (CMC) in surfactants or Critical Aggregation Concentration (CAC) in polymers. Accurately determining CAC is vital for utilizing polymers in molecule encapsulation, but precise measurement is challenging, requiring multiple techniques. Initially, CAC was probed via turbidity measurements, dynamic light scattering (DLS), and isothermal calorimetric titration (ITC), yielding a range of 0.0015 to 0.01 %. Micro-scale thermophoresis (MST) was then employed for the first time to define CAC more precisely, facilitated by the intrinsic fluorescence of modified gum Arabic. Using MST, CAC was pinpointed at 0.001 % (w/v), a novel approach. Furthermore, MST revealed a low EC50 value of 0.007 % (w/t) for self-assembly, signifying uniformity among GAC sub-units and assembly stability upon dilution.

Structure, gelation, and antioxidant properties of curcumin-doped casein micelle powder produced by spray-drying.

The encapsulation of curcumin in micellar caseins (MCs) and the production of powder were performed by spray-drying. Nearly 97% of the curcumin was retained and the yellow powder showed a typical high casein powder morphology. The hygroscopic properties were determined, slight differences reflected less available hydrophobic sites when curcumin was bound to casein, favoring interactions with water in curcumin-enriched MC powders. No difference was detected on the internal MC structure via SAXS. The antioxidant activity of doped-curcumin powder presented 88% of active curcumin. For 60 days at 40 °C storage, the antioxidant activity of curcumin measured by ABTS and FRAP assays was preserved with a percentage of 82 ± 2.0% and 84 ± 1.1%, respectively. Curcumin doped powders presented similar features to classical casein powders (rehydration and gelling abilities). It was demonstrated that curcumin encapsulation in MCs in its powder form helped in protecting its antioxidant activity without influencing the techno-functional properties of MCs. This study allowed the incorporation of curcumin via the MC matrix as an active food ingredient available in a powder state usable as classical milk powder in several food formulations.

Structure and gelation properties of casein micelles doped with curcumin under acidic conditions.

In this study, the ability of micellar casein (MC) to interact with curcumin during acidification and to produce acid gel was investigated. Steady-state fluorescence spectroscopy of curcumin variation and fluorescence quenching of caseins upon binding with curcumin molecules were evidenced. Increasing the temperature from 20 to 35 °C enhanced MC-curcumin interactions as reflected by the increase in the binding constant from 0.6 ± 0.3 × 10(4) to 6.6 ± 0.6 × 10(4) M(-1). From changes in entropy, enthalpy and Gibbs free energy, hydrophobic interactions were proposed as major binding forces. Static fluorescence MC quenching was demonstrated for the MC-curcumin complex during acidification. From pH 7.4 to pH 5.0, the binding site numbers varied in the range from 1.25 ± 0.05 to 1.49 ± 0.05 and the binding constant kb varied from 3.9 ± 0.4 × 10(4) to 7.5 ± 0.7 × 10(4) M(-1). Small angle X-ray scattering profiles demonstrated that the MC internal structure was unchanged upon curcumin binding. The ζ-potential value of curcumin-doped MC indicated that curcumin did not modify the global charge of MC particles. Acid gelation studied by oscillation rheology and static multiple light scattering at 20 and 35 °C led to a similar behavior for native and curcumin-doped MC suspensions. For the first time, it was demonstrated that the colloidal and functional properties of MC were unchanged when doped with curcumin during acidification.