Internal and external factors affecting the crystallization, gelation and applicability of wax-based oleogels in food industry

In recent years, wax-based oleogelation has appeared as a new and effective strategy to structure liquid oil into soft, solid-like systems, which can be exploited as alternatives for trans- and/or saturated lipidic hardstocks in the production of lipid-based food products. Waxes are crystalline gelators, consisting of a mixture of straight-chain alkanes, long-chain fatty acids, long-chain fatty alcohols, wax esters, aldehydes, ketones, glycerol esters or di-esters. Wax-based gelation arises from the crystallization of wax particles. Tuning the preparation conditions such as cooling rate, shear rate and setting temperature can alter the crystallization and gelation of natural waxes in liquid oil. A better fundamental understanding on wax-based oleogelation is therefore important to control the quality of food products, in which these oleogels could act as structuring agents. In the food industry, wax-based oleogels can be utilized to partially or fully replace the trans- and/or saturated fats in fat-based food formulations such as shortening, margarine, confectionery products, ice-cream, and whipped-cream. Furthermore, oil migration can be prevented by using wax crystals to capture the free liquid oil within a fat-based confectionery filling. The scope of this review is to provide a concise insight into structuring liquid oil using natural waxes, with the emphasis on different internal and external factors affecting the physicochemical properties of wax-based oleogels. The innovative food applications of wax-based oleogels are also discussed in details. Wax-based oleogelation has been emerged as a potential alternative to conventional oil structuring. The gelling behavior of natural waxes in liquid oils is governed by the polarity of the solvents, and by the wax crystal morphologies, which are determined by the nature and chain length of the chemical components present in waxes. In addition, the gelling behavior of wax-based oleogels can be tuned by altering the cooling and shear rates, and by changing the time and temperature of cooling. These factors strongly influence the physicochemical properties as well as the storage stability of wax-based oleogels. In addition, the application of wax-based oleogel in food formulations has encountered some technical challenges due to the incompatibility between oleogels and saturated fats, and due to the insufficient amount of solid content provided by waxes. With regard to the sensorial aspect, the waxy mouthfeel might be an obstacle restricting the acceptance of wax-based products in food markets. This review therefore provides a concise overview relating to the internal (chemical composition of natural waxes, type and polarity of solvents) and external factors (cooling rate, shear rate, storage time, and co-structuring) affecting the crystallization and gelation of wax-based oleogels, as well as their potential application in producing low-saturated fat products in food industry.