Fabrication of Curcumin-Loaded Dairy Milks Using the pH-Shift Method: Formation, Stability, and Bioaccessibility.

Abstract

The pH-shift method is a simple approach for incorporating certain kinds of polyphenol-based nutraceuticals into already existing colloidal systems. The polyphenols can be loaded into hydrophobic particles due to the fact that their water-solubility is relatively high under alkaline conditions but low under acid or neutral conditions. In this study, it was demonstrated that bovine milk could be enriched with curcumin using this approach, without adversely affecting milk fat globule stability. The storage stability of the curcumin-enriched bovine milk was assessed when samples were incubated for 60 days at different pH values and temperatures. The pH-stability was determined by storing curcumin-enriched milk at 4 °C for 60 days at pH 6.5, 7.0, and/or 8.0. At this low storage temperature, all milk samples were stable to fat globule aggregation, creaming, curcumin degradation (<13% loss), and color loss. The temperature-stability was determined by storing curcumin-enriched milk at pH 7 for 15 days at 4, 20, 37, or 55 °C. Curcumin breakdown decreased with decreasing storage temperature: 55 °C (43%) > 37 °C (21%) > 20 °C (10%) > 4 °C (5%). Interestingly, the color of the curcumin-enriched milks incubated at 4, 20, and 37 °C remained similar to that of the initial samples, but the sample stored at 55 °C showed significant color fading. Curcumin bioaccessibility determined using an in vitro gastrointestinal tract was around 40%, which was attributed to some chemical degradation and binding of the curcumin reducing its stability and solubilization. This study shows that a hydrophobic nutraceutical (curcumin) can be loaded into dairy milk products using a simple method, which could facilitate the creation of novel functional foods and beverages.