Structural characterization and formation mechanism of zein-propylene glycol alginate binary complex induced by calcium ions

Effect of calcium ions (Ca2+) on characteristics of zein-propylene glycol alginate (PGA) binary complex was studied in this work. Ca2+ induced the formation of zein aggregates with decreased fluorescence intensity and a significant a-helix loss of zein. Zein-PGA binary complex with Ca2+ showed the decreased dimension and the minimum size was observed at 50.0 mM Ca2+. Ca2+ resulted in the formation of strong hydrogen bonds between zein and PGA, strengthened their hydrophobic interactions, and induced a new peak at the diffraction angle of 30 in the pattern of Zein-PGA binary complex. PGA fortified with Ca2+ exhibited an overall plane-like structure, also an interwoven flat profile appeared in Zein-PGA binary complex with Ca2+. Three potential mechanisms were proposed to explain the morphological changes of samples after Ca2+ addition: (i) particle particle collision and aggregation of particles; (ii) chain-chain association and further cross-linking of associated chains; (iii) simultaneous cross-linking coupled with aggregation.