Abstract: Oleogels formed by the solidification of vegetable oils in the presence of gelators can reduce the use of trans and saturated fatty acids and increase the content of unsaturated fatty acids in foods. They can also be a promising hydrophobic nutraceutical delivery vehicle in the food industry. The development of food-derived oleogel gelators is a hotspot of food research. In this study, the feasibility of a mixture of monoglyceride (MG) and stigmasterol (ST) for structuring sunflower seed oil was evaluated. Then, the effects of gelator composition, concentration and storage temperature on the textural, rheological and thermal properties of oleogels were systematically investigated as well as their influence on the efficacy of oleogels in protecting lutein against ultraviolet (UV) radiation. It was found that MG/ST ratio had a significant influence on the lowest mixture concentration for forming oleogels. When the gelator concentration was more than 4%, oleogels could be formed at all tested MG/ST ratios. At the storage temperature of 5 ℃, the hardness, viscosity and chewiness values of the MG or ST oleogels were higher than those of the MG-ST oleogels. As the storage temperature increased to 20 ℃, these textural properties of the MG-ST oleogels were improved. In the rheological assay, all oleogels exhibited a shear-thinning behavior with similar rheological properties. The gelation temperature depended on the composition and concentration of the MG-ST mixture, instead of the storage temperature. The oleogel with the MG/ST ratio of 2:8 possessed the highest gelation temperature (80 ℃). The gelation temperature of MG-ST oleogels declined with the decrease of ST concentration. We also found that oleogels could significantly improve the stability of lutein under UV radiation; the best effect was observed at the MG/ST ratio of 8:2. These results are helpful to develop new edible oleogels and promote the application of lutein in foods.

Key words: oleogels, monoglyceride, stigmasterol, sunflower seed oil, lutein