Design and fabrication of oleogel (Trans fatty acid free solid oil) from hydrolyzed cellulose derivatives

Abstract

Abstract Background: Fat and oil contribute significantly to the final texture and flavor of food products. Hydrogenated oils containing high trans fatty acids (TFAs) are usually used to obtain suitable textural properties in food products. But, the intake of saturated and TFAs has been linked with an increased risk of chronic diseases. Recently, oleogels or structured oils have gained more attention. Ethyl cellulose (EC) is a polymeric oleogelator with the glass transition temperature (Tg) between 130-150 °C. The high melting temperature (Tm) of oleogel can negatively affect the sensory qualities and oxidative stability of food products. This study investigated the impact of hydrolysis on the structural and physicochemical properties of EC and modified EC-based oleogels were examined. Materials and Methods: EC solutions of 3 wt.% were prepared in 70% ethanol/acetic (v/v) acid solvents in the volumetric ratio of 70:30 and 50:50 in order to perform partial hydrolysis at two different temperatures, 65 and 95 °C for 30 minutes. After that ethanol residues and acid residues were removed from the samples. The hydrolyzed EC (H-EC) was vacuum dried for 48 h at 40 °C to dry completely. The oleogels were prepared with mixing of 6 wt.% of EC powders as control and H-EC samples in soybean oil. The samples were heated up to 150 °C under a nitrogen atmosphere to attain a clear oily liquid and EC powder completely disappeared. Then, the oil was cooled to 20 °C at a rate of 1 °C/min using a heating/cooling water bath. Oleogel samples were further analyzed after being incubated at 4 °C for 24 h. After this time, intrinsic viscosity, gel permeation chromatography (GPC), thermal stability using differential scanning calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction were

performed for powders, and oil binding capacity, thermal stability using DSC, size and morphology of crystals and rheological tests were performed for oleogels. Results: Differential scanning calorimetry (DSC) and capillary viscometer results revealed that EC hydrolysis significantly decreased Tg and intrinsic viscosity. FTIR spectra of hydrolyzed EC (H-EC) revealed a breakdown of many glycosidic bonds. The oleogels were prepared by H-EC at the concentration of 6 wt%. Results showed that hydrolysis conditions significantly affected oleogel formation and strength. An optimal oleogel structure was achieved with H-EC at 65 °C, 50/50 solvent ratio (H-EC65/50). The rheological analysis of H65-50/50 oleogel showed higher strength and a lower melting temperature range than EC oleogel. Microscopic observations confirmed that the H65-50/50 forms a new structure with many small cavities, probably the main reason for the firmer gel. Conclusion: The present work introduced an efficient method for modifying the texture and Tm of EC-based oleogel. Based on the intrinsic viscosity and GPC results, hydrolysis decreased the molecular weight of EC, which indicates the breaking of glycosidic bonds. The hydrolysis at mild temperature (65 °C and a ratio of 50:50 ethanol/acetic acid as a solvent led to the formation of a strong oleogel structure and at the same time with a lower Tm range in comparison with unhydrolyzed EC oleogel. Since reducing the melting point of EC is important in the preparation of oleogel and its industrial application, the results of this study can be useful in this regard. Of course, more studies are needed to clarify the effect of hydrolysis conditions on EC structure. Keywords: Ethyl cellulose, Oleogel, hydrolysis