1. Introduction
Polyunsaturated fatty acids (PUFA), particularly those of omega-3 fatty acids (ω-3 FA) are extremely susceptible to oxidation due to the presence of multiple double bonds (Frankel, Satue-Gracia, Meyer, & German, 2002). However, increasing PUFA content in food products has been of particular interest due in part to the reduced risk of heart disease and stroke associated with an increased intake of PUFA content (Stone, 1996). The American Heart Association (AHA) suggests that increasing the ω-3 FA content of food products, particularly EPA and DHA, can lead to a reduced risk for development of cardiovascular diseases (Stone, 1996). The increased interest to include higher levels of ω-3 FA signifies that improving the oxidative stability of these susceptible groups is of importance not only to the food industry but to other industries employing these various lipids such as pharmaceuticals and cosmetics. It is also important to note that PUFA-rich lipid sources are not easily used in the same fashion as saturated fat sources (Willett & Akoh, 2019). Thus, research is needed to help develop PUFA-rich lipid sources with physicochemical properties similar to saturated fat sources. If the oxidative stability of those PUFA-rich lipid sources can be improved it will enhance and increase their use in many products in the future.
One possibility for improving the physical characteristics of a particular PUFA source while also improving the oxidative stability is through the formulation of oleogels. Due to their chemical structure, PUFA usually have melting points below 0 ̵̊C, but by physically converting those PUFA into oleogels with the use of gelators, they can form semi-solid gels at ambient temperatures. The gelators chosen for the purpose of this research were monolaurin and a mixture of monoacylglycerol and diacylglycerol (MAG/DAG). The selected gelators performed best against a battery of other potential gelators in a screening test prior to the onset of this study. To the best of our knowledge these gelators have been included in limited research for the purpose of food grade gels. MAG/DAG has been studied while monolaurin has been used in niche studies as a medicinal gel (Mancuso et al., 2020).
Monolaurin has a known HLB value which falls in the lipophilic range (~7) (Park et al., 2018), while the HLB value for the combination of MAG/DAG will depend on the actual composition of different MAG and DAG included as well as the ratio of the two in the gelator used. However, MAG and DAG are commonly used emulsifiers. Monolaurin has also been reported to possibly enhance the oxidative stability of lipid matrixes (Moradi, Tajik, Razavi Rohani, & Mahmoudian, 2016). The selected ω-3 FA-rich lipid source, algal oil fromSchizochytrium spp. , also has not been well researched in terms of its use in the formulation of food-grade gels. Oleogels present a unique approach to solve oxidative stability issues while also developing desired physical characteristics for lipid sources rich in PUFA (Willett & Akoh, 2019) . Another underutilized processing technique explored in this study is the formulation of emulsion gels (emulgels). Emulgels present unique challenges with experimentation due to the presence of water in sample matrix, but they also possess the same benefits oleogels confer but in an emulsion form. Such gels open more possibilities for use as food ingredients or for use in cosmetic and pharmaceuticals.
The objective of this study was to formulate oleogels and emulgels withSchizochytrium algal oil and analyze the physicochemical characteristics of these gels. To our knowledge no oleogels or emulgels have been developed using this lipid source. If the physical properties of the developed gels are suitable for use as a replacement of saturated fat sources, then these gels may well prove useful in food, pharmaceutical, and the cosmetic industry. The oxidative stability of gels was also studied to determine if any protective effect was achieved. Once gels are developed and the physicochemical characteristics are better understood additional research could potentially allow for these gels to be used in a wide range of applications.