Optimization of grape seed oil Oleogel production using beeswax and monoglyceride

Solid fats such as shortening and margarine have been extensively utilized in the food industry since they play important roles in the quality attributes by providing a unique texture, flavor, and aroma. It is however well-recognized that large intakes of solid fats may cause a variety of adverse health effects such as risk of cardiovascular diseases due to their high levels of saturated fatty acids and also possible presence of trans fatty acids. Therefore, solid fat replacers with low saturated fatty acids and the same qualities to the original saturated fats are necessary. In recent years, research dealing with oleogelation has considerable interest from the researchers in the food sciences (Park et al., 2018). Oleogels can be formed by the self-assembly of organogelators into three-dimensional networks that entrap an organic liquid through capillary forces. They can be produced due to physical forces and chemical interactions depending on the kind of gelators (Cerqueira et al., 2017). Different substances such as lecithin, sorbitan tristearate, monoacylglycerides, a mixture of phytosterol and oryzanol, ricinelaidic acid, fatty acids, fatty alcohols, 12-hydroxystearic acid, wax esters, and waxes can be produced oleogels with edible oils. Organogels as fat mimetics were suitable in different foods, such as ice cream, cookies, sweet bread, frankfurters, and heat resistant chocolate (Valoppi et al., 2017). Beeswax like other waxes is able to play as an edible gelator for producing different edible oils. Beeswax is a complex mixture of chemical compounds predominantly based instraight-chain monohydric alcohol compounds with carbon chains from C24 to C36 and straight-chain acids with carbon skeletons of up to C36, including some C18 hydroxyl acids that can be esters, diesters and triesters. Beeswax organogels have ability of aroma maintenance successfully (Martines et al., 2016). Monoglycerides are lipid molecules consisting of a fatty acid esterified to the hydroxyl group at the glycerol backbone. The use of monoglycerides as structuring agents have gained significant interest due to their ability to gelation of aqueous and non-aqueous solvents based on the potential of monoglycerides to crystallize and cocrystallize either in the bulk phase or at the interfaces. Generally, the crystallization of fatty acid alkyl chain can be achieved either through supersaturation or supercooling of the monoglycerides in oil dispersions (Sintang et al., 2016). The aim of this study was to investigate the production of oleogels from grape seed oil using beeswax as oleogelator, and monoglyceride as surfactant.

Refined grape seed oil was purchased from the local market (Isfahan, Iran), and beeswax and monoglyceride was obtained from merck Co. All other chemicals and solvents were of analytical grade and purchased from Merck Co. and Sigma Aldrich. Oleogels were prepared by mixing grape seed oil with beeswax and monoglyceride. The mixtures were heated at 80 °C in a water bath for at least 10 min to completely dissolve waxes. After that time, the samples were stored at 20 °C for 24 h to form gel and kept at this temperature up to perform the analyses. In this study, the effect of beeswax (0, 0.8, 6.15, 8.6, 10.42, 12.5%) and monoglyceride (0, 0.8, 6.15, 8.6, 10.42, 12.5%) on oil migration, melting point, melting enthalpy, firmness and maximum force for back extrusion of grape seed oil oleogels was investigated using Response Surface Methodology and Design Expert in the form of a central composite design with 5 central points. Optimum and control (margarine) samples were evaluated and compared in terms of physical and textural properties (oil migration, melting point, firmness, maximum force for back extrusion), rheological properties, and polarized light microscopy using SAS ver: 9.0 software. Oil migration of samples were determined according to Fayaz et al (2017). Organogel firmness was measured by a puncture test at 20 °C using an Instron 4301 Universal Testing machine. The rheological analyses were performed according to method described by Lupi et al (2013). The infrared spectra of the organogels were analyzed using FT-IR Spectrophotometer. The samples were scanned in the range of 350 to 4000 cm-1. Micrographs of organogels were obtained under polarized light optical microscope connected with a Leica EC3 digital camera.

The results of this study showed that the beeswax and monoglyceride concentrations had a significant effect on the physical and textural properties of grape seed oil oleogel, so that by increasing the concentration of beeswax and monoglyceride, the oil migration and melting point of oleogels decreased and increased, respectively. An increasing in melting enthalpy, firmness and maximum force for back extrusion were observed in higher levels of beeswax and monoglyceride. The interaction effect of beeswax and monoglyceride concentration in increasing the melting point was weaker than their independent effects. The interaction effect of beeswax and monoglyceride concentration at their higher levels increased the maximum force for back extrusion. Optimal conditions for the production of grape seed oil oleogel with physical and textural properties similar to margarine were 2.1% beeswax and 6.3% monoglyceride. The results of FTIR showed hydrogen bonding has been effective in forming a gel network of grape seed oil by trapping oil droplets. Oleogel and control sample had no significant difference in terms of oil migration, melting point, firmness and maximum force for back extrusion (P>0.05). Evaluation of rheological properties revealed that, by increasing shear rate, apparent viscosity of the oleogel and control samples decreased, which presented the pseudoplastic behavior of samples. The elastic modulus (G′), of oleogel and control samples were higher than viscous modulus (G″) in evaluated frequency range. The elastic modulus, complex modulus and complex viscosity of oleogel were lower than them in margarine. Therefore, margarine had more solid-like properties than the grape seed oil oleogel. Microstructure examination showed the formation uniform and stronger gel network with smaller crystals in oleogel compared to the control sample.

According to the results of the present study, it can be concluded that the use of appropriate concentrations of beeswax and monoglyceride can produce of a structured edible oils with physical and textural properties similar to commercial margarine. So, it selected as a substitute for margarine and shortening, and can be used in producing of healthy food products.