Oil gels are obtained by heating and mixing oils and solid waxes, followed by cooling. They are mainly used in stick cosmetics, such as lipsticks, foundations, and antiperspirants 1) . Hydrocarbon waxes, such as paraffin waxes and synthetic waxes, are mainly used as gelling agents for oil gels 2,3) . However, the replacement of hydrocarbon waxes by botanical waxes from the point of view of substitution by renewable resources and regulation of petroleum-or mineralderived ingredients in the cosmetic industry is desired.However, the oil gel hardness of botanical waxes (such as rice bran wax, carnauba wax, and candelilla wax) is much lower than that of petroleum-derived waxes 4) . Many studies have been conducted to improve the gel hardness of botanical wax. Mixing different types of waxes sometimes causes gel hardness to vary. For example, a mixture of higher alcohols and fatty acids 5) , a mixture of candelilla wax and carnauba wax 4) , the addition of high-purity esters to candelilla wax 6) , and the addition of high-melting-point alcohols to rice bran wax 7) , can improve gel hardness.Gel hardness can be increased by removing impurities from the botanical waxes and obtaining only the main component. Currently, highly purified botanical waxes, such as hydrocarbon and ester mixture extracted from candelilla wax, and hydrocarbon extracted from rice bran wax are commercially available. However, the gel hardness of these highly purified waxes is still lower than that of commercial hydrocarbon waxes.
Compositing organic materials, such as plant pigments with inorganic carriers, can increase the dispersion, stability, and leaching resistance of pigments into solvents. Layered clay minerals are commonly used as inorganic carriers 1,2) . Conversely, mesoporous silica, porous silica with uniform nano-sized pores, has a pore size close to the molecular size of plant pigments and a high surface area (>1,000 m 2 /g).
IntroductionPickering emulsification, in which powders are used as emulsifiers, is applied in various industrial applications as a surfactant-free emulsification method 1,2) . In Pickering emulsification, the powder particles gather at the interface between the oil and water and form a tough layer; hence, the emulsified droplets of the obtained emulsion hardly coalesce. Various types of oils can be emulsified using a single powder.In cosmetics, inorganic powders such as silica and mica, whose surfaces have been hydrophobized with organic materials, are commonly used for liquid foundations and sunscreen emulsions 3−6) . Recently, various cosmetic ingredients have shifted from petroleum-or mineral-derived materials to plant-derived materials, which are renewable resources with low environmental impacts. Therefore, it is desirable to use plant-derived powders, such as cellulose, for Pickering emulsification.Pickering emulsification with cellulose nanofibers obtained from pulp has previously been reported 7−9) . In addition, emulsification with nanofibers obtained from edible plants such as banana peels, oil palm fruits, and seaweeds has been investigated. Edible dried powders without nanofiber treatment, such as pickled plums and avocado fruits, have also been used for Pickering emulsification 10−13) .
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