Structural characterization and stability of microencapsulated flavonoids from Lycium barbarum L. leaves

Lycium barbarum L. leaves are rich in flavonoids, which have been proven to show poor stability and solubility in the external and gastrointestinal environment. To improve the stability and water-solubility of Lycium barbarum L. leaves flavonoids (LBLF), sodium alginate (SA) and chitosan (CS) were utilized as the wall materials to prepare the microcapsules of LBLF (M-LBLF) by polyelectrolyte cross-linking method. The spectrum of Fourier Transform Infrared spectroscopy (FT-IR) showed M-LBLF had an absorption peak at 1735 cm^-1, which might be the electrostatic interaction between the positive and negative charges of SA and CS. X-ray diffraction (XRD) spectrum showed the diffraction peak at 2θ = 51.8° was due to the microencapsulation and transformation of the amorphous structural part into a crystalline state. As demonstrated by Differential Scanning Calorimetry (DSC), the M-LBLF displayed wider and higher endothermic peaks due to the electrostatic interaction between SA and CS. The release of main monomers from M-LBLF in different stages of the in vitro digestion were detected, and it was shown that M-LBLF could resist the digestion in simulated oral fluid (SOF) and gastric fluid (SGF), and enhance the slow-release ability of LBLF in simulated intestinal fluid (SIF), indicating that microencapsulation can improve the stability of LBLF and play a slow-release role. Practical Application: Microencapsulation greatly enhanced the stability of flavonoids and played a sustained release role, which provides a method for the application of Lycium barbarum L. leaves flavonoids as a functional food ingredient. (author)