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

•Calcium ions (Ca2 +) led to the formation of zein aggregates with the loss of α-helix.•Strong hydrogen bonding was formed between zein and propylene glycol alginate (PGA).•An interwoven flat structure was observed for Zein-PGA binary complexes with Ca2 +.•Three formation mechanisms were proposed for Zein-PGA binary complexes induced by Ca2 +.

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 α-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.

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