Effect of ethylcellulose and polyglycerol polyricinoleate concentration on microstructure and oxidative stability of sesame oil oleogel

Abstract
Background and Objectives: Most of the vegetable oils are liquid in the room temperature. Investigations about novel structuring methods of liquid oils are necessary due to the need of food industry to texturized fats with plastic and semi-solid texture in ambient conditions. There are different methods to produce semi-solid fats including, hydrogenation, blending, and interesterification. The mentioned methods have some advantages or disadvantageous. In the vegetable oil industry, there is the desire to use new methods of producing texturized fats. Oleogels obtained from vegetable oils using polymer and surfactant is an alternative for common structuring ways, with the aim of reducing saturated and trans fatty acids intake through the diet.

Materials and Methods: In this study, oleogels with six different formulas were prepared. The first 3 ones were made with sesame oil (80, 85 and 90%) and ethylcellulose (10, 15 and 20%); the others were prepared with the same oil contents and the mixtures of ethylcellulose and polyglycerol polyricinoleate, 3:1. Atomic force microscopy was utilized to image the microstructure of the oleogels. Fatty acid profile of prepared gels was determined by gas chromatography. The oleogels were stored at different conditions (ambient temperature and refrigerator). Their peroxide and thiobarbituric acid values were determined after production and every 30 days during 2 months storage.

Results: The investigation of apparent properties showed that by the increase in ethylcellulose concentration, the strength of gel network was increased. PGPR addition to formulations resulted in increased plasticity and decreased the stickiness of the gels. Microscopic images showed an organized network of ethylcellulose strands which trapped liquid oil. As ethylcellulose concentration increased, continuous network of polymer strands was formed. A decrease in thickness of ethylcellulose strands was observed upon PGPR addition and more homogenous and uniform gel network was formed. Results showed no significant differences between the fatty acid profile of sesame oil and its oleogels. In shelf life studies, by increasing concentration of ethyl cellulose, peroxide values of prepared oleogels tended to decrease. Peroxide and thiobarbituric acid values of the oleogels were increased during storage conditions. The oleogels in the refrigerator had lower peroxide values. Further research is needed to understand secondary oxidation process of the oleogels.

Conclusion: As a general result, it is possible to produce food-grade oleogels from sesame oil, ethylcellulose, and PGPR. It seems such gels have a great potential to use in the formulation of texturized fats and margarines and they are healthy alternatives for various types of hydrogenated oils.