1. Introduction
Mayonnaise is among the oldest and most widely used sauces in the world today and is mainly prepared by mixing egg yolks, vegetable oil (soybean oil, sunflower oil, olive oil, and coconut oil), vinegar (distilled white vinegar), sugar, and salt to maintain a closely packed foam of oil droplets [
1]. The total fat content in mayonnaise can be as high as 70–80%, of which the fatty acids are mainly long-chain and saturated fatty acids [
2]. The consumption of low-fat food products has become more popular over the past decade. Because the amount and type of fat consumed are of importance to the etiology of several chronic diseases, such as obesity, cardiovascular diseases, and cancer, it is not surprising that consumers hold fast to nutritional guidelines concerning fat consumption. The food industry has been forced to reduce the amount of fat, sugar, cholesterol, salt, and certain additives in the diet. The development of healthy mayonnaise has become a trend because of concerns about consumer susceptibility to body health. It is possible to choose fat substitutes in specific quantities that produce a texture close to that of traditional mayonnaise.
In most European countries, the olive tree is among the main agricultural crops, principally for extra virgin olive oil (EVOO) production. The International Olive Council (IOC) has classified olive oil trees based on their purity and quality [
3,
4]. As such, the characterization, especially the flavor and fatty acid composition, of olive oil is very vital and widely studied [
5,
6,
7]. Olive oil is usually characterized by various carbonyl substances, such as linear saturated and unsaturated aldehydes and alcohols, esters and hydrocarbons [
8]. Furthermore, this bioactive composition of olive oil can be altered by geographical origin [
9], ripening degree [
7,
10], extraction methods [
11], cultivar and harvest year [
5,
12]. As mentioned before, previous studies demonstrated that olive oils contained triolein (28.60–48.25%), and significant differences in triglyceride composition based on cultivar and harvested year, even in the same geographical area, microclimatic, and agronomic conditions [
5,
7].
Meanwhile, due to the unique fatty acid profile, soybean oil plays a crucial role in daily life. As with olive oil, the quality of soybean oil also depends on the variety of the origin of seeds, growing condition, region, and conditions of industrial processing. Triglycerides are an essential part of the daily diet, a main source of energy, and they act as carriers of fat-soluble vitamins (A, D, E, and K) [
13]. By using reverse-phase high-performance liquid chromatography (RP-HPLC) analysis, previous studies discovered 12 different fragments of triglyceride present in soybean oil, namely linoleic-linolenic-linolenic (LLnLn), linoleic-linoleic-linolenic (LLLn), linoleic-linoleic-linoleic (LLL), oleic-linoleic-linolenic (OLLn), palmitic-linoleic-linolenic (PLLn), oleic-linoleic-linoleic (OLL), palmitic-linoleiclinoleic (PLL), oleic-oleic-linoleic (OOL), palmitic-oleic-linoleic + stearic-linoleic-linoleic (POL + SLL), palmitic-palmiticlinoleic (PPL), stearic-oleic-linoleic (SOL) and oleic-oleic-oleic (OOO) [
14].
Medium-chain fatty acids (MCFAs) are composed of fatty acids with 6–12 carbons [
15]. Their digestion and absorption in the human body do not require cholic acids or pancreatic lipolytic enzymes for metabolism, and the lymphatic system is not required for transport; instead, MCFAs enter the liver directly via the hepatic portal vein and are rapidly β-oxidized, which increases diet-induced thermogenesis [
16]. Many studies have used MCFAs in the diet to improve food function in recent years. One study demonstrated that consuming 48 g of medium-chain triglycerides (MCTs) compared to corn oil at a single time leads to a greater rise in postprandial oxygen consumption compared to the basal level [
17]. Furthermore, consuming 18–24 g of MCTs for 16 continuous weeks significantly lowers endpoint body weight and fat mass in overweight men and women [
18]. Thus, MCFAs can favorably reduce the accumulation of body fat and increase the expenditure and decomposition of body fat, thereby improving the effect of diet control in overweight patients. Papamandjaris et al. reported that MCFA diets improve the efficiency of adipose oxidation in healthy female adults compared with long-chain fatty acid diets, and suggested that MCFAs should be included in recommended diets to control obesity [
19]. Ham et al. investigated the effect of an MCFA extract on 3T3-L1 adipocytes to explore the mechanism of regulating body weight and body fat formation. As results, MCFAs affected the proliferation of adipocytes by regulating lipoprotein lipase and lipocytic differentiation proteins, thereby regulating the production of animal body fat [
20]. Previous reports have suggested that MCFAs/MCTs preserve insulin sensitivity in animal models and patients with type 2 diabetes [
21].
The favorable effects of MCFAs on regulating body fat have been demonstrated in human, animal, and cellular experiments; to the best of our knowledge, only a few studies have substituted MCTs for edible oil to make mayonnaise, but the variety of processed foods made from MCFAs remain limited. Identifying a suitable fat replacer when formulating low-fat products is important because reducing fat content can deteriorate quality, leading to poor texture, mouthfeel, and flavor [
22]. Plant oils and animal oils (EPA and DHA) with long-chain unsaturated fatty acids are commonly used to make mayonnaise and provide favorable characteristics [
23,
24,
25]. Therefore, in this study, MCTs were used to prepare functional low-fat mayonnaise, and the physicochemical properties of the mayonnaise were determined.
2. Materials and Methods
2.1. Materials
Eggs, edible vinegar (distilled white vinegar), salt, sugar, soybean oil (Taiwan Sugar Co., Tainan, Taiwan; year of production: 2021; 600 mL per bottle; transparent polyethylene oil bottles), and first cold-pressed olive oil (Canoliva extra virgin olive oil, Baena, Spain; year of production: 2021; 500 mL per bottle; opaque glass oil bottles) were purchased from Taisuco, and PXMart (Taichung, Taiwan). Furthermore, MCTs of coconut oil were provided by Extra Crown GFEE International Co. Ltd. (Taipei, Taiwan) which contained 0.27% hexanoic acid (caproic acid), 48.24% octanoic acid (caprylic acid), 38.92% decanoic acid (capric acid), and 11.15% dodecanoic acid (lauric acid).
2.2. Preparation of the Mayonnaise
An amount of 30 g of egg yolks, 19.64 g of apple cider vinegar, 5.77 g of white granulated sugar, and 2.24 g of table salt were weighed in a beaker. The mayonnaise emulsion was prepared by slowly blending the oil with the pre-mix (water phase). The mixture was mixed evenly by stirring for 30 sec in a laboratory grade high-speed dispersion homogenizer (BS-014, Boh Sheuan Enterprise Co., Ltd., Tainan, Taiwan), at the speed of 500 rpm, and 155.88 g of blended edible oil was added according to
Table 1. MCTs replaced the soybean and olive oils at levels of 50% of the total oil used. Next, the mixture was homogenized at a constant speed for 5 min. The prepared mayonnaise was packaged in sealed bags and stored at 4 °C in the dark.
2.3. Composition Analysis
The approximate nutritional composition of mayonnaise samples, which is the moisture, fat, protein, ash, and carbohydrate content were studied in 3 replicates and corresponded to the official methods of AOAC. The moisture content was evaluated by the hot-air oven method; ash content was analyzed by the method of incinerating samples in a muffle furnace at 550–600 °C; crude protein content was studied by the Kjeldahl method or Kjeldahl digestion method; fat content was measured by the acid hydrolysis method; cholesterol content was tested by the digitonin method; while the carbohydrate was determined by subtracting the sum of moisture, protein, fat, and ash percentages from 100%. Caloric values were calculated as: total calories = (4 × g protein) + (9 × g fat) + (4 × g carbohydrate).
2.4. Color Analysis
The color of the mayonnaise samples was analyzed by the Color Meter ZE-2000 (Nippon Denshku Industries, Tokyo). L* (lightness measurement), a* (greenness–redness value), and b* (blueness–yellowness value) value was studied to determine the quality changes. Calibration of the instrument involved using a standard black-and-white ceramic tile before measurement. Color measurements were carried out at room temperature in triplicate.
2.5. Rheological Properties
2.5.1. Flow Test
A dynamic rheometer was utilized for the measurements following the method reported by Liu et al. [
26]. The flow index was measured using a 40 mm stainless steel parallel plate and a 2° cone plate at a temperature of 25 °C and a plate height of 1 mm. The shear rate was set to increase from 0 to 150 (1/s) over 4 min, remain at 150 (1/s) for 4 min, and decrease from 150 to 0 (1/s) over 2 min. The Herschel–Bulkley model was used to calculate yield stress (τy), viscosity (K), the fluid behavior index (n), and thixotropic properties.
2.5.2. The Oscillation Test
The method reported by Liu et al. was used as a reference [
26]. First, the stress sweep was determined. The strain value in the linear viscoelastic region was set to 1%, and an oscillation test was conducted in the frequency range from 0.1 to 10 Hz. The relationships between the G’ (storage modulus) and the G” (loss modulus) and frequency were determined.
2.6. Particle Size Analysis
The method reported by Worrasinchai et al. was used as a reference [
27]. A 150 mL aliquot of 0.1% sodium dodecyl sulfate solution was added to a beaker containing 0.04 g of mayonnaise. After the solution was mixed evenly, the opacity was adjusted to 0.2%–0.5% with deionized water, and the particle size and distribution of the sample were measured using a laser particle size analyzer at a speed of 1200 rpm, a refractive index of the sample of 1.46, and a measurement time of 10 s.
2.7. Emulsion Stability
The method reported by Mun et al. was modified to determine emulsion stability [
28]. Five g of mayonnaise was placed in a centrifuge tube and the tube was stored in an incubator at 50 °C for 48 h. Then, the sample was centrifuged at 1600 rpm for 10 min and weighed after removing the oil layer.
2.8. Sensory Evaluation
Sensory analysis was conducted on the mayonnaise samples after 1 day of storage at 4 °C. Sixty students (30 males, and 30 females; age range 18 to 25 years; no smoker) from the Department of Food and Nutrition, Providence University, were selected as test evaluators to assign scores after attending a 4 h training session before the evaluation. The factors used for the evaluation included appearance, aroma, taste, greasiness, and overall acceptability, which were evaluated on a 9 points hedonic scale of 1 = the least, the lowest, and 9 = the most, the highest. The samples were arranged and coded with three-digit random numbers. Furthermore, the serving order was completely randomized. The contents of the evaluation form were fully explained before the evaluation, and warm water and soda crackers were provided as palate cleansers.
2.9. Statistical Analysis
Experimental assessments and analyses were carried out in triplicate. Experimental data were analyzed with Duncan’s new multiple range test using SAS software (SAS Institute, Cary, NC, USA) to compare the differences between treatment. A p-value < 0.05 was considered significant. All experiments were performed in triplicate, and data are expressed as the mean ± SD.