The effect of oil type and solvent quality on the rheological behavior of zein stabilized oil-in-glycerol emulsion gels

Abstract

The aim of this study was to assess the effect of oil type and solvent quality on the structure formation and rheological properties of zein-stabilized oil-in-glycerol emulsion gels. To change the interactions within the system, four types of oil (medium chain triglyceride (MCT) oil, sunflower oil, extra virgin olive (EVO) oil, and castor oil) with different polarity were used, and the solvent quality was modified by temperature and water addition. In all cases, emulsion gels were obtained with G' > G''. At each protein concentration and oil content, the gel strength and crossover strain γco increased with an increase in oil polarity, indicating the formation of a stronger gel structure and higher stability against structure breakdown. These results are related to the fact that a higher oil polarity decreases the oil-protein hydrophobic interactions and thereby increasing the interactions between the proteins to form a strong network in the continuous phase. In addition, water addition to the continuous phase enhanced the gel strength and the resistance against structure breakdown for more apolar MCT oil, while the opposite results were observed for the more polar castor oil. The zein-based emulsion gels showed a thermo-responsive behavior, and different responses in structure collapse and rearrangements during heating and cooling were found for different oils. These simple approaches form an interesting route to tune the rheological properties of zein-based emulsion gels.