Effect of calcium ions on rheological properties and structure of Lycium barbarum L. polysaccharide and its gelation mechanism

The objectives of this study were to identify the chemical composition, monosaccharide composition, and molecular weight (Mw) of the polysaccharide (LBP) extract from Lycium barbarum L., and investigate the effects of Ca2+ on the zeta potential, rheological properties, infrared spectra (IR), and structure as well as the gelation mechanism of the LBP. The results showed that the LBP was an acidic glycoprotein mixture with an Mw of 4.05 x 10(5) Da. The addition of Ca2+ first decreased and then increased the absolute value of zeta potential. The elastic modulus (G'), complex viscosity (ri*), and stress relaxation modulus (G(t)) of LBP increased with an increase of Ca2+ concentration, and reached the maximum value at the concentration of 12 mM. IR showed that the typical peak wavenumber of the LBP has changed in the presence of Ca2+. SEM and AFM analysis confirmed that Ca2+ could improve the formation of gel network structure in LBP. In addition, the electrostatic interaction and the calcium bridges produced by the addition of Ca2+ played a key role in the formation of the gel network structure. These findings will benefit the application of LBP in the food and pharmaceutical industries.