Rubisco at interfaces II: Structural reassembly enhances oil-water interface and emulsion stabilization

Rubisco is the most abundant protein on earth and has gained extensive attentions as a novel food ingredient, such as an emulsifier. Extraction methods can significantly affect its molecular structures and consequently influence its oil-water interface and emulsion stabilization properties. This work aims to elucidate the role of the Rubisco molecular structure in stabilizing the oil-water interface and the multiphase system of emulsions. Ultrafiltration (mild) and acid precipitation-alkaline redispersion (extensive) were used to extract Rubisco from spinach leaves. Protein molecular properties were characterized by size exclusion chromatography (SEC), circular dichroism (CD), and fluorescence spectrometry. Subsequently, the oil-water interfacial properties, including the adsorption and rheological behavior in both small and large dilatational and shear deformations, and the emulsion stabilization properties of Rubisco were investigated. We found that acid precipitation-alkaline redispersion produced a Rubisco extract (RA) with extensive structural reassembling, compared to the one produced by ultrafiltration (RU), for which nativity was mostly retained. RA had two-fold higher surface hydrophobicity than RU, and this caused RA to adsorb faster to the oil-water interface and developed a stiffer solidlike interface (Gi' = 26 +/- 3 mN/m) than RU (Gi' = 15 +/- 2 mN/m), which was also more resistant to density changes in large dilatational deformations. Consequently, RA displayed higher emulsifying activity and emulsion stability to coalescence during bulk shear and storage. Additionally, structural reassembly resulted in a higher value of the zeta potential of RA, which made the emulsion more stable against flocculation, compared to RU. Our study demonstrates that structural reassembly might be a useful strategy to improve the behavior of plant proteins in oil-water interface and emulsion stabilization, and may stimulate the development of new plant protein-stabilized emulsion-based products.