The oil in aqueous ethanol emulsion as a routeto zein-stabilized thermos-responsive oleogel: Principle and application

Research output: Book/ReportPh.D. thesisResearch

Aside from the urgency of transitioning towards a diet more based on sustainable ingredients,it is necessary to provide novel solutions for healthier alternatives to the current foodingredients. Fats, as one of the most important food ingredients, have always been a challengefrom the technical point of view to be reduced or substituted in food formulations. The flavor,mouth feel, and texture of food are highly affected by the fat content. Therefore, the substitutionof fats without compromising the quality of the final food product has been challenging.Oleogels have been introduced as a solution for substitution of the solid fat rich in saturatedfatty acids. Oleogels are unsaturated oils that are structured into a gel-like system by usingdifferent kinds of oleogelators and methods to mimic the physicochemical properties of solidfats.The present Ph.D. thesis focuses on the development of the emulsion-templated oleogelationmethod to stabilize sunflower oil by using the hydrophobic protein zein. The application ofproteins to stabilize an oleogel not only can increase the nutritional profile of oleogels but canalso introduce new rheological and functional properties that are not achievable by otheroleogelators.In the present thesis, an oil-in aqueous ethanol emulsion, as an intermediate system in oleogelpreparation, was stabilized by using zein protein. The stability window was evaluated bymeasuring the oil droplet sizes as an effect of zein and ethanol concentration. Static lightscattering (SLS), Coherent Anti-stokes Raman Scattering (CARS) microcopy, and imageanalysis were used for this purpose. The stability of emulsions increased with adding morezein, while it was adversely affected by increasing the ethanol content (50-90(%v/v)). Thesurface activity of zein was found to be determined as an interplay between zein solubility inethanol/water and the effect of ethanol on the interfacial tension. The optimum surface activityof zein was found at 70%v/v ethanol.The zein-stabilized oleogels are characterized in Paper ΙΙ and it is attempted to understand theemulsion-templated method using zein protein. Oleogels with a high capacity of holding oil inthe structure were successfully prepared by evaporating the volatile continuous phase ofemulsions at room temperature. The CARS microscopy was combined with image analysis andallowed investigation of the intact microstructure of oleogels containing different ethanol andzein concentrations and also an understanding of the microstructural changes during thetransition from emulsion to oleogel. The formation of a highly stable emulsion that remainsstable upon drying was found critical in this method.The rheological properties of the zein-stabilized oleogel were modified by glycerol addition.Paper V explores the effect of glycerol and zein content on the gel strength, thermal behavior,and microstructure of oleogels. The gel strength of oleogels decreased with increasing theglycerol content, however, the plasticizing effect of glycerol and its mechanism was foundconcentration dependent. Increasing zein concentration increased the gel strength and oil-holding capacity of oleogels. Zein-stabilized oleogels showed reversible thermos-responsivebehavior as seen by oleogels became softer upon heating, probably due to the weakened proteininteractions and increased solubility in glycerol at high temperatures. This could allow theprotein to restructure with cooling without any major change in the secondary structure of theprotein after heating to 100 °C.Lastly, the application of glycerol-plasticized oleogel in the fermented Pea protein isolate (PPI)gel. The effect of using oleogel on the microstructural, textural, and rheological properties ofthe plant-based cheese was compared with un-gelled sunflower oil, coconut fat, and the dairycheese, Burgo de Arias as the reference system. All lipid sources provided similar hardness inPPI gel while the dairy cheese hardness was significantly higher due to the natural differencein the dairy and plant-based protein interactions. However, the gel strength of PPI gelcontaining oleogel and dairy cheese was similar. Therefore, it was suggested that zein-stabilized oleogel can provide similar textural properties as fresh dairy cheese.Overall, this Ph.D. thesis introduces a new method to use ethanol-soluble proteins to stabilizeoleogels and suggests an oleogel texture modifying approach to improve the rheologicalproperties of oleogels.
Original languageEnglish
PublisherDepartment of Food Science, Faculty of Science, University of Copenhagen
Number of pages198
Publication statusPublished - 2023

ID: 337599816