pH-driven fabrication of a caseinate–pectin polyelectrolyte complex as a promising carrier for lutein and zeaxanthin delivery: Microencapsulation, stability, and sustained release properties

In this study, caseinate-pectin polyelectrolyte complexes and co-solutions were successfully fabricated at pH 3.0 and 7.0, respectively, to encapsulate bioactive molecules. During the fabrication process, the effect of the sequence in which each component was added on lutein/zeaxanthin (Lut/Zx) complexation with sodium caseinate (NaCas) was investigated. The protective effect of the polyelectrolyte complex and co-solution for Lut/Zx in liquid formulations was compared with that of a binary system containing only caseinate and Lut/Zx. Compared with the binary system, the polyelectrolyte complex at pH 3.0 further enhanced the chemical stability of Lut/Zx during storage, whereas the co-solution at pH 7.0 did not exhibit this ability. Unexpectedly, NaCas-Lut/Zx - pectin (NC-L/Z-P) with a theoretically sandwich structure did not exhibit better protection than NaCas-pectin-Lut/Zx (NC-P-L/Z). Fluorescence quenching spectra revealed that the addition of NaCas to Lut/Zx and ultimately to pectin resulted in the formation of a sandwich structure, which was soon followed by structural rebalancing. Finally, freshly prepared NC-L/Z-P complexes were lyophilized to stabilize their sandwich structure, resulting in improved encapsulation and sustained-release properties compared with those of the dried NC-P-L/Z. These results suggest that protein-polysaccharide complexes, combined with timely dehydration, enhance the combination of Lut/Zx with caseinate, leading to heightened protective effects.