Citric acid cross-linked zein microcapsule as an efficient intestine-specific oral delivery system for lipophilic bioactive compound

To improve the stability of zein core-shell structure microcapsule and realize intestine-specific release of lipophilic bioactive compounds , the β-carotene-loaded microcapsule was prepared by zein cross-linked with citric acid (CA) for the first time. The antioxidant activity of β-carotene was not affected by preparation process. Compared to uncross-linked microcapsule (UCM), the CA cross-linked microcapsule (CCM) had higher β-carotene encapsulation efficiency (94.4% vs. 91.4%), greater shell thickness (161 nm vs. 140 nm) and denser shell structure. Additionally, the CCM had better stability under thermal, freeze-thaw and ionic strength treatments. The fourier transform infrared spectra (FTIR) and circular dichroism (CD) analysis showed that there existed hydrogen bonding and interactions between zein and CA, and differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data revealed the thermal stability and crystallinity intensity of zein/CA complex were improved. The CCM was more stable in simulated gastric fluids and β-carotene bioaccessibility was significantly improved in simulated intestine fluids (72.4% vs. 48.5%).