Comparison of Oleogels Obtained by Emulsion Template Method Using Low Molecular Weight Hydroxypropyl Methylcellulose (HPMC) with Fish and Vegetable Oils

Abstract

Introduction

Cardiovascular disease remains the leading cause of mortality worldwide. One of the associated risk factors is the consumption of fats, particularly trans and saturated fats [1,2]. Their widespread use in processed foods, such as margarine, shortenings, and baked goods (cookies, biscuits, cakes), is due to their low cost and favourable physicochemical properties [1].

Trans and saturated fat intake should not exceed 1% and 10% of total caloric intake, respectively, with replacement by unsaturated lipids recommended to reduce the risks of heart disease, type 2 diabetes, and obesity [1,3]. Several countries, including Denmark, Lithuania, Poland, Saudi Arabia, and Thailand, have implemented regulations to eliminate trans fats from industrial food production [4]. The replacement of trans and saturated fats poses a significant challenge for the food industry, as they provide structural integrity and solid texture to diverse products [5]. A promising strategy is the structuring of oils into oleogels. These semi-solid systems reproduce the textural attributes of animal fats while being enriched in unsaturated lipids and containing reduced levels of saturated and trans fats [6]. For food applications, oleogels typically consist of more than 90% oil by mass [7]. This enables formulation from healthy oils (sunflower, canola, and fish) rich in polyunsaturated fatty acids with potential cardiovascular benefits. The successful development of oleogels requires a comprehensive understanding of the physicochemical properties of both the oils and the gelling agents. Accordingly, a wide range of preparation methods (direct, indirect, and semi-direct), gelling agents (e.g., fatty acids, waxes, xanthan gum, polysaccharides), and oils (e.g., sunflower, canola, olive, soybean, fish) have been investigated.

Most polymers used in the food industry are predominantly hydrophilic (such as native and many modified starches, proteins, gums, etc.), and therefore cannot structure oils directly [8]. Consequently, indirect methods have been developed, taking advantage of the diversity, availability, and physicochemical properties of food polymers. One of the most widely employed approaches is the emulsion template method. This involves preparing a stable oil-in-water (O/W) emulsion stabilized by a gelling agent, followed by the removal of water through drying methods such as convective, vacuum, or freeze drying [9]. The dried semi-solid material is then gently homogenized to obtain the oleogel [10].

Hydroxypropyl methylcellulose (HPMC), a cellulose-derived amphiphilic polymer substituted with hydroxypropyl and methoxyl groups, exhibits affinity for both water and nonpolar molecules [11]. Generally Recognized As Safe (GRAS) and widely used in pharmaceutical, cosmetic, and food industries, HPMC is cost-effective and associated with health benefits including reductions in cholesterol and postprandial glucose and insulin levels [12,13].

In recent decades, there has been increasing interest in incorporating fish oil into the human diet due to its high content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3 polyunsaturated fatty acids exhibit protective effects against cardiovascular disease, diabetes, asthma, arrhythmias, and atherosclerosis [14,15]. Nevertheless, intake of these compounds remains below recommended levels for many individuals [15]. Fish oil can be obtained from lipid-rich subproduct valorization of both fishing captures and aquaculture, increasing the opportunities of incorporating this oil into foods for human consumption.

Fish oil oleogels formulated with natural waxes have been previously studied by dissolving the waxes in the oil phase at elevated temperatures, followed by cooling to form the oleogel [16,17]. In contrast, the preparation of such oleogels using the emulsion template method remains unexplored. This study evaluates the rheological, textural, and physical properties of fish oil oleogels prepared with varying HPMC concentrations via the emulsion template method and compares them with the properties of sunflower oleogels prepared with the same method and structuring agent.

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Materials

Fish oil obtained from the skin and bones of Japanese mackerel (Scomber japonicus) was provided by the Marine Research Institute (IIM-CSIC). Sunflower oil was acquired in a local market. Hydroxypropyl methylcellulose (HPMC) with low molecular weight was employed with a viscosity of 80–120 cP in a 2% (w/v) aqueous solution at 20 °C and with methoxy and hydroxypropyl groups at proportions of 28.7% and 9.1%, respectively.

4.2. Preparation of Emulsions

Oil-in-water emulsions were prepared at several concentrations of HPMC (1.5, 2.0, and 2.5% w/w). All emulsions (100 g) were prepared at the highest oil-to-water ratio able to produce oleogels avoiding phase separation during emulsion preparation or during the drying step. This aspect is relevant because the use of the minimum water fraction reduces the energy consumption during drying for oleogel production. Fish and sunflower oleogels were able to be developed with maximum oil-to-water ratios of 40:60 and 50:50 (w/w), respectively.

Emulsions with sunflower oil were prepared according to the procedure described by Saavedra et al. [34]. HPMC was first dispersed in the oil phase using a four-blade stirrer (IKA-WERK RW 20 DZM, Staufen, Germany) at 280 rpm for 7 min. Cold water (~10 °C) was then gradually added over 1 min while stirring, allowing effective polymer hydration. The mixture temperature was maintained at 25 °C using a controlled water bath during homogenization using a high-energy dispersion unit (Ultraturrax T-25 Basic, IKA-WERK, Staufen, Germany) at 9500 rpm for 15 s, followed by a second cycle at 21,500 rpm for 40 s. During homogenization, the mixture was simultaneously stirred using an orbital shaker (Rotaterm, Selecta, Barcelona, Spain) at 120 rpm. Emulsions with fish oil were prepared following the same protocol, but homogenization was performed at 35 °C to decrease the oil viscosity and to approximate the rheology of fish oil to sunflower oil. Finally, the emulsions were allowed to stand at room temperature for 20 min to stabilize its microstructure before further analysis.

4.3. Formation of Oleogel

After the resting period, emulsions were convective air dried to yield the oleogel. Emulsions were spread in Petri dishes (11.5 cm diameter) at 0.20 cm thickness (18 g/dish). Drying was performed in a convective air dryer (Angelantoni Challenge 250, Massa Martana, Italy) at 80 °C, 10% relative humidity, and 2 m/s air velocity until the moisture content was less than 0.01 g H₂O/g dry solids.

The resulting dried solids were homogenized at 6500 rpm until uniform paste formation with no uncrushed particles, yielding final HPMC concentrations of 3.6, 4.9, and 5.8% (w/w) in the case of fish oil oleogels and 2.9, 3.8, and 4.7% (w/w) for sunflower oil oleogels. Samples were then transferred to plastic ice cube trays and stored at 2 °C until analysis.

Escobar, A.; Montes, L.; Franco-Uría, A.; Moreira, R. Comparison of Oleogels Obtained by Emulsion Template Method Using Low Molecular Weight Hydroxypropyl Methylcellulose (HPMC) with Fish and Vegetable Oils. Gels 2026, 12, 319. https://doi.org/10.3390/gels12040319

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