Chitin nanofibers improve the stability and functional performance of Pickering emulsions formed from colloidal zein

There is growing interest in formulating Pickering emulsions from biopolymer particles due to consumer demand for more natural products. Protein-based colloidal particles can be used for this purpose, but they are prone to aggregate at pH values around their isoelectric point (pI), which limits their application. In this study, the possibility of using chitin nanofibers (ChNFs) to improve the pH stability of Pickering emulsions prepared from zein colloidal particles (ZCPs) was investigated. Initially, the morphology and interfacial properties of the complexes formed between ChNFs and ZCPs were studied as a function of pH (3-9). The tendency of the ZCPs to aggregate and sediment at pH ≥ pI was reduced in the presence of ChNFs, which was attributed to the formation of electrostatic complexes. The contact angle of the composite particles could be optimized by altering their composition. For instance, the contact angle increased from 74° for ZCPs to 85° for ZCP/ChNF (5:1 ratio) at pH 6, which improved their tendency to stabilize the oil droplets. Brewster angle microscopy indicated that ZCP/ChNF complexes had rod-like and/or particulate structures at an air-water interface, which were different from those observed in the bulk aqueous phase. Pickering emulsions formed from ZCP/ChNF complexes had better stability than those formed from ZCPs or ChNFs, especially when the pH was close to or greater than the pI. An in vitro digestion study showed that the presence of the interfacial complexes reduced the lipolysis of the oil droplets by about 11% in a simulated gastrointestinal tract. High internal phase Pickering emulsions (HIPPEs) could be formed from ZCP/ChNF complexes at pH ≥ pI, which were able to protect unsaturated lipids from oxidation. Overall, our results show that chitin nanofibers can be used to improve the pH stability of Pickering emulsions formed from colloidal zein, as well as to modulate their functional performance.