مقایسه‌ی امولژل‌های آب در روغن حاوی اولئوژلاتورهای مختلف برای اصلاح چربی مورد استفاده در کیک مافین شکلاتی

Introduction: Fats are essential components in the formulation of many food products and often contain high levels of saturated and trans fatty acids. The excessive consumption of these fats is associated with adverse health effects, including becoming overweight, elevated blood cholesterol, diabetes, and cardiovascular diseases. Accordingly, the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) have recommended that the energy intake from saturated and trans fatty acids should not exceed 10% and 1% of total daily calories, respectively. Furthermore, a concurrent rise in consumer awareness regarding nutrition and health has led to an increased demand for low-fat and low-calorie food products. Nevertheless, the elimination or reduction of fat poses a significant challenge for food scientists, as fats play a vital role in developing desirable texture, flavor, and sensory properties, particularly in bakery products. To overcome this challenge, various gelled systems have been explored. Oleogels, formed by structuring vegetable oils into solid-like materials using oleogelators, have emerged as a promising approach. Oleogels can mimic the physical properties of solid fats while containing lower levels of saturated and trans fats. However, since they are composed of over 90% oil, oleogels remain high in calories, limiting their application for calorie reduction. A more advanced strategy involves the use of emulgels, which are gelled emulsion systems. Specifically, water-in-oleogel (W/O) emulgels offer a dual benefit: they provide the structure of a solid fat while also reducing caloric content by incorporating a dispersed aqueous phase within the continuous oleogel phase. This structure is crucial for maintaining a fat-like sensory perception, as the continuous oil phase interacts directly with the sense of taste. The physicochemical properties of these emulgels depend on the chemical composition of the oleogelators, the type of oil, and the production process conditions. Waxes, such as beeswax (BW) and rice bran wax (RBW), are common oleogelators, but their use alone can be challenging. Therefore, the addition of a suitable emulsifier is critical for creating stable systems. Glycerol monostearate (GMS), a non-ionic, lipophilic surfactant, can act as both an emulsifier and an oleogelator. Despite the great potential of W/O emulgels, research on their application in bakery products has been limited, with most studies focusing on oil-in-hydrogel systems. Muffins, as one of the most popular bakery products, typically contain high levels of fat (15-20%) and serve as an excellent model for investigating novel fat replacement strategies. This study was therefore designed with two primary objectives. First, to develop and characterize W/O emulgels structured with either beeswax or rice bran wax, with and without the addition of GMS as an emulsifier. The second objective was to evaluate the impact of replacing 25% of the margarine in a chocolate muffin formulation with the selected emulgels on the final product's physical and sensory properties.
Material and methods: Glycerol monostearate (GMS), potassium iodide, and starch were sourced from Merck (Germany). Rice bran wax (RBW) was obtained from H&B Oils Center Co., and beeswax (BW) was procured from a local market in Tabriz, Iran. Cold-pressed sunflower oil (Borooje brand, Iran) was used as the oil phase. All other reagents, including hexane, ammonium thiosulfate, acetic acid, and chloroform, were supplied by Mojallali Co. (Iran). Four W/O emulgel formulations were prepared: a beeswax-based emulgel (BWE), a beeswax-based emulgel with GMS (BWGE), a rice bran wax-based emulgel (RWE), and a rice bran wax-based emulgel with GMS (RWGE). The formulations were developed based on the method described by Pandolsook and Kupongsak (2017) with modifications. The oil phase was prepared by heating the oleogelators (9% w/w of either BW or RBW) and, where applicable, the emulsifier (1% w/w GMS) in cold-pressed sunflower oil for 10 minutes in an 80°C water bath. A 25% (w/w) aqueous phase (deionized water), also heated to 80°C, was then added to the oil phase. The mixture was homogenized at 12,000 rpm for 5 minutes in 50°C. The resulting emulgels were cooled to room temperature and stored at 5°C until further analysis. The microstructure of the emulgels was observed using a light microscope at 1000x magnification. The firmness of the emulgels was measured using a back-extrusion test performed with a Tensile Tester-SUT 2.5N (Sanaf, Iran). Differential Scanning Calorimetry (DSC) was used to analyze the thermal behavior of the emulgels on a DSC-400 instrument (Sanaf, Iran). The physical stability of the emulgels was assessed by measuring their ability to hold oil and water (Solvent Holding Capacity). The peroxide value (PV) of the emulgels and the pure sunflower oil was measured on day 1 and day 30 of storage at 25°C using the AOCS official method (Cd 8-53). Four muffin formulations were prepared: a control made with 100% margarine and three treatments where 25% of the margarine was replaced by the selected emulgels (BWE, BWGE, and RWGE). 45 g of batter was weighed into each paper mold and baked at 165°C for 20 minutes in a convection oven. After cooling, the muffins were analyzed for moisture content, firmness, and sensory attributes. Moisture was determined by drying approximately 2 g of each muffin sample in a hot air oven at 105°C until a constant weight was achieved. Muffin firmness was evaluated using a compression test with the same instrument used for the emulgels. Sensory attributes (texture, color, taste, and overall acceptability) were evaluated by a panel of 15-20 semi-trained assessors using a 5-point hedonic scale. All experiments were performed in triplicate in a completely randomized design. Data were subjected to a one-way analysis of variance (ANOVA), and means were compared using Duncan's multiple range test at a 95% confidence level (p<0.05) with SPSS software (version 27).
Results and discussion: The macroscopic properties of the emulgels are directly influenced by their underlying microstructure. Microscopic analysis confirmed that all four formulations were W/O emulgels, characterized by water droplets dispersed within a continuous oil phase. A clear distinction was observed between the two wax types. The beeswax-based emulgel (BWE) exhibited smaller and more uniformly distributed water droplets, with a mean particle size of 3.43 µm, while the rice bran wax-based emulgel (RWE) had significantly larger and more heterogeneously distributed droplets with a mean particle size of 6.55 µm. This difference is attributed to the higher content of surface-active free fatty acids and fatty alcohols in beeswax. The superior microstructure of the beeswax emulgel directly correlated with its mechanical properties. The BWE sample (2.29 N) was significantly firmer than the RWE sample (0.88 N), a result of the denser gel network formed by finer crystals and reinforced by the smaller water droplets acting as "active fillers." This enhanced network integrity also led to superior physical stability, with BWE showing an oil holding capacity of 98.69% compared to 69.8% for RWE. Due to its surface-active properties, the addition of glycerol monostearate (GMS) had a significant and positive impact across all analyses. GMS incorporation significantly reduced the mean water droplet size in both wax systems, down to 1.98 µm in BWGE and 4.74 µm in RWGE. This reduction in particle size directly led to a significant increase in gel firmness, with the BWGE sample being the firmest at 3.51 N. The improved stability was also evident in the oil holding capacity of BWGE, which was 100%. Furthermore, GMS enhanced oxidative stability; after 30 days of storage, the samples followed the trend BWGE (5.91 meq O₂/kg) < BWE (6.27) < RWGE (8.83) < RWE (9.19), indicating a direct correlation between gel firmness and resistance to oxidation. Finally, DSC analysis confirmed the superior structural integrity of the GMS-containing systems, with the addition of GMS leading to higher melting peaks and thus enhanced thermal stability.The application of these emulgels as partial fat replacers in muffins yielded products with significant improvements in quality attributes. All muffins containing emulgels had a significantly higher moisture content (ranging from 25.12% to 26.93%) compared to the control muffin (22.15%). This higher moisture resulted in a softer texture, with all three emulgel-based muffins being significantly softer than the control (27.92 N). The BWGE-M was the softest (15.26 N), followed by BWE-M (19.53 N) and RWGE-M (22.32 N). These textural improvements are considered highly desirable in cake-like products. Crucially, these benefits were achieved without compromising consumer perception. The sensory panel found no significant differences in taste, texture, color, or overall acceptability between the control and the reformulated muffins. Notably, the BWE-M and BWGE-M samples obtained higher scores than the 100% margarine control in most sensory parameters, including texture, taste, and overall acceptability.
Conclusion: The evaluation of the emulgels demonstrated that beeswax, compared to rice bran wax, resulted in emulgels with greater firmness and more favorable physical and oxidative stability. Furthermore, the addition of glycerol monostearate played a key role in enhancing the emulgels' properties by reducing droplet size, reinforcing the gel network, and increasing thermal stability. Moreover, replacing 25% of the margarine with the beeswax-based emulgels (BWE and BWGE) in the chocolate muffin formulation improved the final product's qualitative attributes. The reformulated muffins had significantly increased moisture and a softer texture, and also possessed an enhanced nutritional profile due to the reduced fat content. Crucially, these desirable textural and nutritional properties were achieved without any negative impact on the sensory acceptance (taste, texture, color, and overall acceptability) of the muffins. It can therefore be concluded that the use of these emulgels is a practical and successful strategy for producing healthier, higher-quality chocolate muffins.