Introduction

Solid fats such as shortening, margarine, butter, lard and tropical oils are necessary ingredients in the formulation of pastries [1]. Fats present a significant role in the structure and geometrization, consequently having an important influence on the texture and sensory aspects of food products [2, 3]. When compared to liquid oil, the use of solid fats minimizes rancidity, leading to final products with better oxidative stability and longer shelf life [4]. Furthermore, baking fats provide various essential functions: capturing air during the kneading process, thus helping in the formation of microstructure and stability of the products; contributes to products fragility by preventing the formation of the gluten network; provides stability by limiting the migration of the lipid phase to the surface of the products [3, 5, 6]. Due to the function of fat to reduce the stickiness of the dough surface and, after melting, the protection of starch granules from gelatinization, pastry fats contribute to the formation of dozens of overlapping layers of dough and fat in section, in puff pastry products [7].

The production process of pastry products requires the use of significant amounts of fat, that vary from 25 to 40%. In addition, with the mentioned technological attributes, these fats can be distinguished by their high content of saturated and trans fatty acids [8, 9]. Excessive intake of saturated and trans fats is widely recognized to increase the risk of developing cardiovascular diseases, coronary heart diseases, obesity, and myocardial infarction [10,11,12]. Also, a high consumption of these fats could increase plasma concentrations of triglycerides, total cholesterol, and low density lipoprotein (LDL) while decreasing high density lipoprotein (HDL) [10, 12, 13]. Due to these negative effects on human health, a number of strategies, and legislative measures have been suggested to reduce and eventually remove the amounts of trans and saturated fats in food. According to the World Health Organization, it is recommended to decrease the consumption of total fats, saturated and trans fats to levels below 30%, 10%, and 1% of total energy intake [14]. The US Food and Drug Administration has determined that partially hydrogenated oils, the primary dietary source of industrially produced trans fatty acids, are not any longer generally recognized as safe (GRAS) for any use in human food [15]. Trans fats can also occur naturally in foods derived from ruminants; therefore, Commission Regulation (EU) 2019/649 sets a maximum limit for all trans fats other than those occurring naturally of 2 g/100 g of fat in food intended for the final consumer and food intended for supply to retail [16].

Due to these actions and regulations, it is essential for food industry to develop and implement new lipid structuring technologies that allow the incorporation of vegetable oils rich in unsaturated fatty acids into food matrix. Thus, in addition to the dietary and nutrition advantages, there is also a decrease or removal of saturated and trans fatty acids in foods [17, 18]. One of the innovative techniques is oleogelation, which is based on the structure of liquid edible oil [19, 20]. Oleogels represent a complex structure in which a continuous phase of liquid oil is immobilised using a gelling agent (at low concentrations of up to 10% by weight) in a three dimensional, thermo-reversible gel network with characteristics comparable with those of solid fats [19, 21,22,23]. Natural waxes are among the most studied agents for structuring edible oils. Carnauba wax is produced from the leaves of the Brazilian palm Copernicia cerifera and is on the Food and Drug Administration list of generally recognized as safe food additives; therefore, it can be used without restrictions other than those imposed by current good manufacturing practice [24, 25].

Due to the widespread consumption of pastry products, the use of oleogels as substitutes for conventional fats, mainly saturated fats, or in some regions partially hydrogenated oils with high trans fat content was already studied for biscuits [26], crackers [27], cookies [2, 28,29,30,31,32,33], croissants [34], muffins [35,36,37], sweet pan bread [38,39,40], tart pastry [41] and cakes [33, 42,43,44,45,46,47]. Due to the lipid phase used, oleogels are a rich source of unsaturated fatty acids. For instance, the structuring of canola oil with 3 or 6% candelilla wax led to the formation of a lipid system with a high content of unsaturated fatty acids of up to 88.9% compared with shortening, which was low in unsaturated fatty acids (36.6%) and high in saturated fat (63.4%) [29]. Jang et al. [2] noticed an improvement in the nutritional profile of cookies formulated with oleogel from canola oil due to a decrease in the content of saturated fatty acids (8.5–10.2%) and an increase in the content of unsaturated fatty acids (89.9–91.5%), in contrast to cookies formulated with shortening (52.8 and 47.2%). Similarly, the partial and total replacement of shortening with sunflower oil and hydroxypropyl methyl cellulose oleogel led to a reduction of up to 45% of saturated fats simultaneously with an increase of up to 47% of unsaturated fatty acids in croissants [34]. Due to the high temperatures used to obtain the oleogels, their oxidative quality also had to be considered. Kim et al. [48] reported a higher oxidation resistance of candelilla/carnauba and beeswax oleogel than Tenebrio molitor larvae oil and olive oil. Lim et al. [49] also reported a higher oxidative stability of oleogels compared to canola oil, a resistance that increased with the increasing hardness of oleogels.

Plant waxes are the most used structuring agents for the production of oleogels with applicability in pastry products. These oleogels have shown the potential to completely or partially substitute conventional fats. Among these, the most used is candelilla wax [2, 28, 29, 31, 37, 38, 44, 46], while, up to our knowledge, only one study has been reported for carnauba wax applicability in pastry products [43]. Consequently, we had selected carnauba wax for obtaining sunflower oil oleogel as an alternative fat, rich in unsaturated fatty acids and to assess its potential as a total conventional fat replacer in pastries: (i) bow tie cookies, (ii) cheese crackers, (iii) apple pie, (iv) cookies, (v) jam-filled puff pastry. We chose this type of products to fit into two categories- tender and puff pastry, and because they are frequently consumed but not well-researched, being reported to date mainly researches on cookies [2, 28,29,30,31,32,33], but, to our knowledge, only limited studies was reported for crackers [27] and puff pastry [34]. Moreover, a comparison was made between these five pastries that were evaluated under the same conditions, whereas the majority of studies analyses a limited number of products. As there are few researches that evaluate in the dynamics of the technological process, we chose to analyze the structural properties of the oleogel in comparison with the conventional fats used to obtain the selected products, and then their influence on the dough-type semi-finished and final products.

In this regard, the aim of the current research was to obtain an alternative fat that could be used to completely replace conventional fats in five different pastry products. Based on this data, the objectives of this research were to: (1) obtain and characterize the structured lipid system composed of carnauba wax and sunflower oil; (2) investigate the impact of replacing conventional fats on dough properties and (3) finished products for five different pastry categories. Since pastries are extensively consumed, the results obtained may provide the basis for future researches regarding the use of structured lipid systems as a total or partial replacement for conventional fats to reduce the amount of trans and saturated fats while maintaining the consumption of unsaturated fatty acids.

Materials and methods

Materials

The ingredients used to obtain tender and puff pastry products were purchased from a local retailer and were: white wheat flour, yeast, salt, eggs, white sugar, sour cream, kneaded cheese, baking powder, vanilla sugar, lemon essence, baking soda, cinnamon powder, wheat semolina, vinegar, golden apples, apricot jam. Conventional fats used in the manufacture of products were: (i) lard with 37% saturated fatty acids, (ii) butter with 82% fat content of which 49.2% saturated fatty acids, (iii) commercial margarine with 60% fat content of which 30% saturated fatty acids, being procured from a local store, while (iv) puff pastry margarine with 80% fat content of which 41% saturated fatty acids, was kindly provided by a local distributor of food ingredients. Oleogel was produced using refined sunflower oil purchased from a local store and carnauba wax (E00018; melting point 82 ℃ and acidity 2–7 mg KOH/g) generously offered by Koster Keunen.

Oleogel preparation

The oleogel (OG) was prepared by the direct method using refined sunflower oil and carnauba wax in a concentration of 10% (w/w). The gelling agent was dissolved in the sunflower oil (SO), by gradually heating the mixture until it reached a temperature of 82 ℃ to completely dissolve the entire amount of wax and form a homogeneous mixture, using a magnetic stirrer plate (500 rpm) with heating (IKA® C-MAG HS7). The mixture was cooled by storing at 4 ℃ for 24 h.

Oleogel and conventional fats characterization

Texture profile analysis

The Brookfield CT3 Texture Analyzer (Brookfield Engineering Labs, Middleboro, MA, USA) was used to evaluate the textural profile of conventional fats and oleogel, according to the method described by Hwang et al. [31] with slight modifications. The oleogel was prepared 24 h prior to analysis and stored at 4 °C, while conventional fats were placed in cylindrical containers and stored overnight at 4 °C. Before analysis, samples were stored for two hours at ambient temperature (20 ± 2 ℃). The determination consists in penetrating the samples (30 mm height × 45 mm diameter), using the TA18 spherical compression probe (12.7 mm diameter), which is attached to a 10 kg compression cell. The samples were compressed at a depth of 10 mm from the sample surface in two cycles at a speed of 1 mm/s, and the compression probe was retracted at the same speed. The results were processed using the instrument software, and the parameters followed in the analysis were: hardness [N], adhesiveness [mJ] and cohesiveness.

Evaluation of rheological parameters

The analysis of rheological properties was performed with minor modifications to the method described by Thakur et al. [23]. The Anton Paar MCR 302 Rheometer (Anton Paar, Graz, Austria) and the serrated parallel plates PP35/P2 were used for evaluating variations in viscoelastic properties. The samples were stored for 2 h at ambient temperature (20 ± 2 ℃) before analysis. The samples were placed on baseplate and compressed to obtain a gap of 1 mm and the excess fat/oleogel was trimmed. Amplitude sweeps measurements in the stress range of 0.01–100% were applied to determine the linear viscoelastic region (LVR) at a frequency of 1 Hz. Samples were allowed to rest for 3 min at 20 ℃ before performing analysis. Frequency sweep measurement was performed in the identified linear viscoelastic region at a constant shear strain of 0.01%, from 0.1 to 10 Hz. The storage modulus (Gʹ) and the loss modulus (G″) were recorded.

Oleogels applicability as a conventional fat replacer in pastries

In this research paper, five different pastry products were obtained: (i) bow tie cookies (tender dough pastry filled with jam)—BTCK, (ii) cheese crackers—CC, (iii) apple pie—AP, (iv) cookies—CK and (v) jam-filled puff pastry (yeast fermented)—PP, which presented in the composition various conventional fats: commercial margarine (CM, in bow tie cookies), a mixture of 73% commercial margarine and 27% lard (ML, in cheese crackers and apple pie), butter (BT, in cookies) and puff pastry margarine (PM, in jam-filled puff pastry). The products were reformulated by totally substitution of conventional lipids with oleogel (OG). The finished products were packed and stored at 18–20 ℃ and a relative humidity of 65–70%, to perform the analysis. The manufacturing process and the appearance of the products can be consulted in the Supplementary files (Online Resource Supplementary Text 1–5, Figs. S1, S2).

Conventional fats or oleogel-based doughs and the corresponding pastry products characterization

Doughs texture profile analysis

The texture profile analysis was carried out using the methodology provided by Mert and Demirkesen [50], with slight modifications. Texture analysis involves deformation of the dough balls (20 mm diameter) in two cycles, using the cylindrical compression probe TA25/1000 (50.8 mm diameter) (Brookfield CT3 Texture Analyzer, Brookfield Engineering Labs, Middleboro, MA, USA). The compression of the conventional and reformulated doughs was performed at a speed of 1 mm/s, at a deformation of 75% from the sample surface and at 20 ℃. The parameters followed in the textural analysis were: hardness [N], adhesiveness [mJ], cohesiveness, resilience and springiness index.

Doughs rheology determination

The rheological characteristics of conventional and oleogel doughs were evaluated using the method described by Jung et al. [38], with minor modifications. The samples were placed between the serrated plates (PP35/P2) of the Anton Paar MCR 302 rheometer (Anton Paar, Graz, Austria) and compressed to a 2 mm gap, the excess dough being trimmed. A serrated geometry was used to prevent the samples from slipping, and they were allowed to rest for three minutes at 20 °C prior to analysis to allow relaxation, due to the stress induced during loading. Frequency sweep tests were performed in the range 0.1–10 Hz, at 20 ℃ and the storage (Gʹ) and loss (G″) modulus were recorded.

Texture analysis of pastries

The textural profile of the obtained pastry products was performed according to the method described by Zhao et al. [51], with slight modifications. The determination consists in compressing in a single cycle the prototypes of bow tie cookies (45 mm length × 35 mm width × 5 mm height), cheese crackers (35 mm length × 20 mm width × 5 mm height), apple pie (45 mm length × 30 mm width × 5 mm height), cookies (30 mm diameter × 10 mm height) and jam-filled puff pastry (40 mm length × 40 mm width × 12 mm height) with the TA7 acrylic knife edge (60 mm width). The Brookfield CT3 Texture Analyzer (Brookfield Engineering Labs, Middleboro, MA, USA) records the load [N] as a function of time [s]. The results were processed using the instrument software, and the parameter followed in the textural analysis of the finished products was hardness [N]. The determination was performed at ambient temperature (18–20 ℃). For the pastry products with filling, the textural analysis was performed of a sheet of baked dough, without filling, which was obtained according to the manufacturing recipe.

Determination of fat losses for doughs and pastry products

The measurement of fat loss was conducted using the methodology provided by Giacomozzi et al. [52], with minor adjustments. The pastries formulated with conventional fats or oleogel, were placed on a filter paper (12 × 12 cm) and stored at ambient temperature (20 ± 2 ℃). The amount of fat losses (grams) was determined based on the difference in the mass of the filter paper, weighed on days 1, 9 and 14 of storage.

Determination of color parameters for conventional fats, oleogel, doughs and pastries

The color analysis was conducted using the portable colorimeter NR200 (3NH, Shenzhen, China) to assess the color parameters L*, a*, and b*. In the measuring system, the parameter L* provides information on the surface brightness (0—black and 100—white), a* refers to the color saturation, where the negative values − a* correspond to the green color and the positive + a* to the red color, and parameter b*, where the negative values − b* correspond to the color blue and the positive + b* to the color yellow [8]. The instrument performed an automatic calibration (L* = 0, a* = 0 and b* = 0). The values ​​L*, a* and b* were provided by the instrument software.

The color coordinates obtained were used to determine the total color difference (∆E) between the conventional and oleogel samples. This parameter was determined on the basis of the formula mentioned in the study conducted by [9]:

$$\Delta E = \sqrt {(L*c - L*x)^{2} + (a*c - a*x)^{2} + (b*c - b*x)^{2} }$$

where: L*c, a*c, b*c represent the color coordinates for the conventional sample; L*x, a*x, b*x represent the color coordinates for oleogel sample.

Saturated fat decrease in pastries

The reduction in saturated fat content was studied after the pastries were reformulated by completely replacing conventional fats with oleogel. Consequently, the total amount of saturated fatty acids from the conventional fat phase or the oleogel system was calculated for each pastry product to monitor the impact of this replacement, while also taking into account technical losses. The total saturated fatty acid content of the lipid phase was expressed as percentage from the finished pastry product (100 g).

Statistical analysis

The rheological measurements were carried out in duplicate, the textural analysis and the assessment of fat losses were performed in triplicate, and the color analysis was conducted in six repetitions. One-way analysis of variance (ANOVA) and Tukey’s comparison test at a significance level of p < 0.05 were used. Differences were analyzed using Minitab Statistical Software. All results were presented as mean ± SD (standard deviation).

Results and discussion

Oleogel and conventional fats characterization

Oleogel appearance

The structure of oleogels can be influenced by the amount and type of gelling agent used, the type of lipid phase, the thermal parameters applied during the obtaining process, but also by the speed, time and cooling temperature of the homogeneous mixture formed [19, 23]. Carnauba wax used in a concentration of 10% (w/w) present the ability to structure the refined sunflower oil, with the formation of a gel structure, semi-solid consistency, opaque, stable, without syneresis, or leaking during inverting the samples for 60 min at room temperature. Therefore, the direct structuring method and the applied parameters were adequate to obtain the structured lipid system (Online Resource Fig. S3).

Textural profile analysis of oleogel and conventional fats

Fats must have plastic properties, a solid consistency and adequate technological properties to be used in the formulation of pastries [9]. In the current study, the textural properties of oleogel (OG) were determined and compared with those of conventional fats, to evaluate the applicability and the potential substitution of oleogel in pastry products.

Hardness is an important textural property for the characterization of solid fats, and it impacts the possible use in pastry products formulation [23]. Hardness [N] is the peak value observed during the first compression cycle and is defined as the force required to achieve a given food deformation [53]. Among all samples, puff pastry margarine showed the highest hardness value (9.78 N), a significantly higher difference compared to the other conventional fats (1.42–2.70 N) and oleogel (2.34 N) (Table 1). These results are similar to those reported by Borriello et al. [21] in which oleogel consisting of pumpkin seed oil and 6% carnauba wax showed a hardness value of 2.37 N and 5.73 N when oleogel was formulated with 8% carnauba wax. On the other hand, beeswax oleogel (olive, linseed and fish oils) reached a higher penetration force of 11.70 N (measured at breaking point) [54] and the use of 8% beeswax in pumpkin seed oil led to the formation of oleogels with a lower hardness value—0.53 N [21]. The firmness of the oleogel (olive oil and cetyl-wax esters) has been found to be 6 N after 24 h at 4 °C. The firmness decreased by approximately 60% during the 20-day storage period, and remained constant until the 30th day (~ 2 N). This may be attributable to the development of large crystals, as evidenced by polarized light microscopy conducted in this study [55]. In our study, oleogel showed similar values, but still slightly lower compared to commercial margarine (2.70 N) and higher than butter (1.53 N) and mixture of commercial margarine and lard (1.42 N). The use of 3% and 6% candelilla wax, led to the formation of oleogels with lower hardness values (< 4 N) compared to those obtained for shortening (~ 10 N), values that had the tendency to increase with the increase level of wax [2]. Lower hardness values were reported for oleogel with hazelnut oil and 5% beeswax (2.73 N) or 5% sunflower wax (4.18 N) compared to commercial shortening (14.21 N) [30]. Thus, the hardness of the sample is influenced by the type of wax and oil used, as well as their interaction. Another important textural parameter of fats used in the formulation of pastries is adhesiveness.

Table 1 Textural properties and color parameters for oleogel and conventional fats
Full size table

Adhesiveness [mJ] represents the strength of the physical attraction between the surface of the product and the surface with which it comes into contact [56]. From a technological point of view, adhesiveness influences the processing and producing characteristics of the dough. For conventional fats, there was a correlation between hardness and adhesiveness values (the adhesiveness values increased together with the hardness values), but despite this, there is no statistically significant difference between them and oleogel, with the exception of puff pastry margarine. Oleogel showed the lowest adhesiveness value (2.30 mJ) compared to conventional fats (4.40–5.17 mJ), especially with puff pastry margarine (21.73 mJ). Also, in the study by Yilmaz and Ogutcu [30] the values of adhesiveness (N) were higher in the shortening sample (8.75 N), compared to oleogels formed with beeswax (2.12 N) and sunflower wax (1.68 N).

Cohesiveness indicates the strength of the product internal bonds, the attraction forces within the same material that hold it together [56]. Conventional fats showed cohesiveness values between 0.45 and 0.71, while oleogel showed a lower value of 0.18, indicating the lowest internal strength of all samples analyzed. According to Glibowski et al. [57], who studied the instrumental textural properties of some conventional fats (butter, margarine, spreads), products with high fat content were the most adhesive and less cohesive, while products with the lowest fat content were less adhesive and most cohesive. In the present study, the most adhesive and less cohesive sample was puff pastry margarine with a fat content of minimum 80%, while the less adhesive and most cohesive was the mixture of margarine and lard with a fat content of 72%. The oleogel presented the lowest values of adhesiveness and cohesiveness, although it has a fat content of 90%, but these results may also depend on the proportion of saturated fatty acids in the composition, so the oleogel has a low proportion of saturated acids (10%) compared to conventional fats (> 30%). Similar values of hardness (2.54 N) and cohesiveness (0.12 N) were reported by Tanislav et al. [58] for oleogel consisting of 10% carnauba wax and sunflower oil, but the value of adhesiveness was reduced (0.55 mJ) compared to that reported in the present study.

Rheological characteristics of oleogel and conventional fats

The storage modulus (Gʹ) was higher than the loss modulus (G″) in the applied frequency range (0.1–10 Hz), suggesting that the samples exhibit a solid behavior with more prominent elastic properties. Both Gʹ and G″ increased slightly in the frequency range used, for all samples. According to data reported in literature, to be classed as a gel system, the elastic component (Gʹ) must be higher than the viscous component G″, so oleogel exhibited a gel-like behavior [23]. When comparing the viscoelastic properties of conventional fats with those of oleogel, it was observed that the oleogel sample had higher values for Gʹ and G″ (3.7710*105 and 7.2149*104 at 1 Hz) results similar, statistically insignificant with those of puff pastry margarine (Gʹ- 3.5105*105 and 6.1175*104 at 1 Hz). Therefore, oleogel was characterized by the strongest gel network, followed by puff pastry margarine, mixture of margarine and lard, butter and commercial margarine (Table 1). Puff pastry margarine exhibited the highest hardness value and concomitant high values of both moduli, in contrast to commercial margarine, which, despite presenting a hardness value similar to that of oleogel, showed significant differences in terms of the storage and loss modulus. The results are similar with those reported by Borriello et al. [21] who observed a gel-like behavior characterized by a more prominently elastic than viscous behavior, for oleogel formed with carnauba wax and pumpkin seed oil and also for oleogels consisting of rice bran wax (9%) and refined corn oil or expeller-pressed corn germ oil [51] and oleogel obtained from carnauba wax (10%) and sunflower oil [58].

Color parameters for oleogel and conventional fats

The color of the oleogel is an essential characteristic for incorporation into pastry products, as it can affect the characteristics of the final product and, consequently, consumer acceptance. In this regard, the color parameters of oleogel and conventional lipids were analyzed and compared. Following a visual examination, all samples were opaque, with conventional fats showing a white-yellow color, in different shades and oleogel displaying a yellow color.

Among the conventional fats, the puff pastry margarine showed the highest value of the L* parameter (89.23), which indicates higher brightness, followed by the mixture of commercial margarine and lard (77.93). Butter and commercial margarine showed similar values (69.43 and 67.82) and in contrast, the oleogel showed the lowest brightness index- 42.46. Positive values of the parameter a* were observed for all studied fats, suggesting a higher proportion of red hue. Oleogel was found to have the lowest red spectrum intensity (a* − 0.61), compared to conventional fats with values in the range of 2.98–3.46. Also, the values of the parameter b* were positive for all samples, indicating higher yellow intensity. The lowest value was found for oleogel (b* − 7.61), followed by commercial margarine (b* − 13.93), mixture of margarine and lard (b* − 15.61), butter (b* − 18.06) and puff pastry margarine (b* − 19.59).

The color differences between conventional fats and oleogel were quantified by calculating the total color difference (∆E). The color difference between each conventional fat and oleogel was over 28 units (Table 1), indicating that the differences between samples were detectable. Onacik-Gur and Zbikowska [9] reported that values of the color difference (∆E) higher than 3 can be observed with the human eyes. The lowest values of ∆E were identified between oleogel and commercial margarine (28.19) and butter (29.02), respectively. In the case of puff pastry margarine and mixture of margarine and lard, ∆E values were higher- 48.36 and 36.45.

Characterization of doughs based on conventional fats or oleogel

Analysis of textural properties

The structural properties play an important role because they impact both the handling and processing of the dough during the technological process as well as the quality of the finished products [59]. The replacement of conventional fats with oleogel affected the hardness of the doughs. The dough for bow tie cookies exhibited a similar hardness value, with a slight decrease in hardness from 11.94 N for conventional dough to 11.87 N for oleogel dough (Table 2). These results are consistent with the textural parameters of the fats, in which oleogel (2.34 N) exhibited a hardness value comparable to that of commercial margarine (2.70 N). A decrease in hardness with the use of oleogel was also observed in the case of dough for cheese crackers, which decreased from 8.97 N (conventional dough) to 6.68 N (oleogel dough), which means that the dough showed a softer consistency and requires lower force for compression. The decrease in hardness values may be attributed to the fact that conventional doughs contain more saturated lipids than oleogel doughs, which contain more unsaturated fatty acids. Also, another factor that could influence the hardness of the dough was the temperature between 30 and 32 ℃, used during the fermentation operation for bow tie cookies and cheese crackers. Mert and Demirkesen [50] reported a decrease in the hardness of doughs formulated with sunflower oil and carnauba/candelilla wax in concentrations of 2% or 5% (38–49 N) compared to that formulated with shortening (58 N). In another study, these authors observed that doughs obtained with candelilla wax at a concentration of 3% and 6% (w/w) presented a lower hardness (42.67–50.63 N) compared to doughs formulated with shortening (62.88 N), but also with those formulated with a mixture of 70:30 and 40:60 oleogel and shortening, which showed values between 50.15 and 57.11 N [29]. In contrast, the oleogel dough samples intended for apple pie, cookies, and jam-filled puff pastry had higher hardness values than conventional doughs, indicating that they were harder and required more force to compress. Therefore, the hardness of the oleogel dough for jam-filled puff pastry increased from 13.07 N to 15.28 N for conventional dough, for oleogel dough for cookies from 9.10 N to 17.54 N, and the highest increase was observed in oleogel dough for apple pie from 14.30 N to 45.24 N. In regards to conventional cookie dough and jam-filled puff pastry, it was expected that the hardness values of these would be higher compared to oleogel doughs. This expectation came from the fact that the manufacturing process involved one or more rest operations at temperatures ranging from 2 to 4 ℃, as well as the use of fats with significantly higher levels of saturated fats (49.2% saturated fatty acids for butter and 41% saturated fats for puff pastry margarine).

Table 2 Textural properties and rheological characterization for conventional and oleogel doughs
Full size table

Conventional doughs showed similar values of cohesiveness, ranging from 0.22 for apple pie to 0.36 for cookies. Statistically insignificant cohesiveness values were observed for conventional and oleogel doughs used to obtain bow-tie cookies and jam-filled puff pastry. In contrast, for the other samples, the substitution of conventional fats with oleogel, resulted in an increase or a decrease in the cohesiveness of the doughs, respectively. In the case of cheese cracker dough, the use of oleogel increased the value of cohesiveness from 0.35 to 0.65, while the values decreased for cookie dough (0.36 and 0.16) and apple pie dough (0.22 and 0.05).

Resilience represents an indicator of how a material recovers from deformation, relative to the applied speed and force [60]. In terms of resilience, conventional (0.02–0.04) and oleogel (0.01–0.07) doughs exhibited similar values, the only statistically significant difference was for cookies. The replacement of conventional fats in cheese crackers and bow tie cookies had no effect on the doughs resilience, which remained at 0.02 value. The oleogel dough for jam-filled puff pastry and cookies showed an increase in resilience compared to conventional doughs (from 0.04 to 0.07 and from 0.02 to 0.04), while the oleogel dough for apple pie exhibited a decrease (from 0.03 to 0.01).

The springiness index indicates the recovery properties of the dough, thus a value of 1 indicates a completely elastic material and 0 value a completely viscous material, being correlated with the adhesiveness [60]. These parameters are very important because they indicate the behavior that the dough will have during the processing operations (rolling and shaping) [58]. Due to the higher adhesiveness of the dough, the bow tie cookies, cheese crackers, and apple pie proved to be more difficult to process during the technological preparation process. The conventional dough samples had similar values for the springiness index, with the apple pie dough having the lowest value (0.17), and the cookie dough having the highest value (0.28). The springiness index for oleogel doughs ranged from 0.08 for apple pie to 0.59 for cheese crackers. Cheese cracker dough with oleogel exhibited the highest adhesiveness value (4.87 mJ) and the most elastic behavior (0.59), compared to conventional cheese cracker dough (2.43 mJ and 0.29). Similarly, the oleogel dough for bow tie cookies showed a higher value of adhesiveness (4.40 mJ) as well as a more elastic behavior (0.27), in contrast to the conventional sample (3.60 mJ and 0.24). For dough samples intended for jam-filled puff pastry and cookies, the complete substitution of conventional fats with oleogel decreased the adhesiveness and springiness. In contrast, in the apple pie samples, the adhesiveness values were similar 1.67 mJ and 1.70 mJ respectively, but the use of oleogel led to the formation of a dough with a more viscous behavior (0.08) compared to the sample with conventional fats (0.17) and also with the other samples (0.12–0.59). Tanislav et al. [58] reported similar values of resilience (0.02), adhesiveness (3.90 mJ), cohesiveness (0.07) and springiness index (0.12) for oleogel dough (carnauba wax and refined sunflower oil) intended for biscuits.

Rheological properties

To evaluate the influence of the total replacement of conventional fats with oleogel on the doughs viscoelastic properties, rheological characteristics were measured. According to the results, the storage modulus (Gʹ) was higher than the loss modulus (G″) in the analyzed range (Table 2), thus the elastic properties were more pronounced compared to the viscous ones. Similarly, Jang et al. [2], reported higher values of Gʹ than G″, values that tended to increase with increasing frequency (0.01–10 Hz). In addition, they noticed higher values of the Gʹ and G″ for the cookie dough sample formulated with shortening, values which, according to them, may be attributable to the shortening firmer texture. In the present study, the apple pie dough had the highest values of both moduli among all samples, with the oleogel dough (Gʹ-4.4931*105 and G″-2.3276*105 at 1 Hz) having higher values than the conventional dough (Gʹ-1.3954*105 and G″-6.7316*104 at 1 Hz) (Online Resource Fig. S4). The results are comparable to those of the textural analysis, in which apple pie dough exhibited the maximum hardness values, with the oleogel dough (45.24 N) showing higher values than the conventional dough (14.30 N). In the case of dough for jam-filled puff pastry, the use of structured lipid system led to the formation of a dough with weaker viscoelastic properties compared to the dough with conventional fat, possibly because the puff pastry margarine presented a slightly lower storage modulus (3.5105*105), but similar to oleogel (3.7710*105) in the rheology of fats. Also, a slight decrease was observed for cheese crackers. The replacement of commercial margarine in bow tie cookies and of butter in cookies led to a slight increase in the viscoelastic properties of the doughs, very probably linked to oleogel high values of storage and loss modulus.

Instrumental color parameters

The values of L*, a* and b* for the doughs varied, as a result of the total replacement of conventional fats with oleogel (Table 3). In the case of oleogel doughs, the parameter L* (brightness) had lower values for all samples compared to conventional doughs. Results are consistent with the lowest value of the oleogels brightness index (L*), as determined by colorimetric analysis of fat samples. For the conventional samples, the highest brightness value was observed in the jam-filled puff pastry (L*- 81.84), followed by bow tie cookies (L*- 80.28), cheese crackers (L*- 79.33), and apple pie (L*- 74.46), the lowest value being for cookies (L*- 69.49). In the case of oleogel doughs, a higher brightness value was observed in jam-filled puff pastry (L*- 79.74), followed by a significant difference in bow tie cookies (L*- 59.97), apple pie (L*- 59.03), cheese crackers (L*- 57.72) and cookies (L*- 55.82). For each sample of dough, the parameters a* and b* had positive values. As a consequence of the complete replacement of conventional fats with oleogel, the values of the parameter a* decreased, with the exception of the dough intended for bow tie cookies, in which the parameter increased from 3.63 to 4.66. Significant differences in the a* parameter were observed in cookie and apple pie doughs, in which the red spectrum color parameters decreased from 7.18 to 5.51 and 7.29–4.95, respectively, with the addition of oleogel. Also, the b* parameter values were lower for the oleogel dough samples, with the exception of the jam-filled puff pastry, which exhibited a 0.02-unit increase in the yellow spectrum color. Therefore, the addition of oleogel had an influence on the brightness index, so that the doughs with oleogel showed a lower brightness and became darker in color due to the addition of the structured lipid phase and also showed lower red and yellow shades, compared to conventional doughs. All of these values obtained for the reformulated doughs correspond to the instrumental color values obtained for the oleogel, which exhibited the lowest values for the L*, a*, and b* parameters.

Table 3 Color parameters and fat losses for conventional and oleogel doughs
Full size table

The maximum total color difference (∆E) was identified in dough for cheese crackers (21.93), while the lowest value was observed in dough for jam-filled puff pastry (2.13). These values are not comparable to the total color difference (∆E) from the fat samples analysis, as the highest differences were observed between oleogel and the margarine and lard mixture (36.45) and puff pastry margarine (48.36). Therefore, with the exception of the jam-filled puff pastry dough, the difference was above the detection limit for all samples, which was also observed during the technological process (soft doughs with oleogel appeared slightly darker).

Fat losses

To determine the physical stability, the fat losses of dough samples produced with oleogel or conventional fats were assessed and compared. From day 0 to day 9, there was an increase in the quantity of oil loss in all dough samples. Instead, after 9 days of storage, there was a decrease in fat losses or a constant maintenance of the values until the day 14 (Table 3). In the case of oleogel dough samples, higher values ​​of fat losses were recorded, up to 12.71 g/100 g (for bow tie cookies), compared to the maximum values ​​recorded for conventional doughs of 7.41 g/100 g (for cheese crackers). In contrast, the lowest loss, for both conventional and oleogel sample, was identified at jam-filled puff pastry- 0.34 g/100 g and 3.29 g/100 g, respectively. In the case of oleogel doughs, the dough for bow tie cookies had the highest amount of fat losses, followed by the dough for cheese crackers, apple pie, cookies, and jam-filled puff pastry, whereas in the case of conventional doughs, cheese crackers had the highest amount of exuded oil, followed by bow tie cookies, apple pie, cookies, and jam-filled puff pastry. This suggests that doughs obtained with oleogel showed a higher exudation of the lipid phase and therefore a lower physical stability compared to conventional doughs. This was also noticed throughout the technical process, when doughs produced with oleogel had a softer and oily texture, with visible lipid phase losses on the doughs surface.

Characterization of pastries based on conventional fats or oleogel

Texture analysis

The textural determination indicated variations in the hardness values of the samples with conventional fats compared to oleogel. Hardness values ​​were between 8.83 N and 19.89 N for conventional products and between 2.37 N and 15.64 N for oleogel products (Table 4). In the case of bow tie cookies, cheese crackers, and apple pie, the use of a structured lipid system resulted in the production of products with lower hardness values than conventional products. The apple pie sheet formulated with conventional fat or oleogel had the highest hardness value of 19.89 N and 15.64 N, respectively, among all the evaluated products. On the other hand, both cookie products had hardness values of 14.91 N (conventional product) and 15.12 N (oleogel product), a statistically insignificant difference. Mert & Demirkesen, 2016a [29] reported a higher breaking force for cookies formulated with candelilla wax oleogel (60.78–69.75 N) and those formed with a mixture of oleogel and shortening (46.39–61.11 N) than those obtained with shortening (41.03 N). In another study, cookies made with candelilla/carnauba wax oleogels required a higher breaking force (59–71 N) than those formulated with shortening, which had a hardness value of 42 N, which was lower than cookies formulated with sunflower oil (84 N) [50]. These results demonstrated that the incorporation of oleogels resulted in the formation of cookies with a stronger texture. According to Mert and Demirkesen [50] a higher cookie hardness may be a consequence of the incorporation and retention of insufficient air in the system. A higher hardness of cookies formulated with rice bran wax oleogels in different concentrations and different lipid phases was reported by Zhao et al. [51] and according to them although the hardness of oleogels increased with the amount of wax added, the hardness of cookies decreased with the increasing concentration of oleogelator. Hwang et al. [31] reported that the hardness values of cookies obtained with different gelling agents and vegetable oils were not significantly different from those formulated with commercial margarine. In contrast, Yilmaz and Ogutcu [30] found that the use of oleogels with 5% sunflower wax and beeswax led to the formation of cookies with a lower hardness (31.85 and 36.89), compared to those formulated with shortening (47.12). Jang et al. [2] reported that a higher force was required to shape cookies formulated with shortening (71.67 N) than samples formulated with oleogel containing 3% and 6% candelilla wax- 63.74 N and 53.74 N, respectively. In our study, the hardness of jam-filled puff pastry samples increased from 8.83 N to 14.68 N when commercial and puff pastry margarine was completely replaced with oleogel. This may be due to the lower capacity of the oleogel to maintain the specific layers, resulting in a more compact and dense structure, as also observed in the section of the finished product. The research conducted by Espert et al. [34] involved the substitution of traditional fat in croissants with shortening (SH) and oleogel (OG- sunflower oil and hydroxypropyl methylcellulose) mixtures (100:0, 50:50, 40:60, 30:70, 0:100). The samples containing the highest amount of fat (SH100:OG0) exhibited the highest peak firmness (7.91 N), which was attributed to the solid character of puff pastry fat at room temperature. In contrast, SH0:OG100 sample exhibited the lowest peak firmness (4.79 N), which may be related to the lack of solid fat crystals in the mixture, resulting in a reduced consistency of the croissants. The firmness of the croissants exhibited a decreasing trend as the concentration of oleogel increased. However, no statistically significant variations in force values were observed among the croissants formulated using SH-OG blends. Thus, the addition of oleogels to croissants results in a reduction in firmness, even with the croissants more compact appearance. All of these results demonstrate that, in addition to the other primary and auxiliary ingredients, fat has significant influence on the textural properties of pastries.

Table 4 Textural properties, color parameters and fat losses of conventional and oleogel products
Full size table

Color parameters

In pastries, color parameters have a major effect, because they impact the visual acceptability of consumers. The total replacement of conventional fats with oleogel led to a change in the color parameters of the finished products surface. Cookies (L*-73.89) had the highest brightness index value among conventional products, followed by apple pie (L*-71.70), jam-filled puff pastry (L*-70.74), bow tie cookies (L*-70.56), and cheese crackers (L*-69.48). All values of parameter a* were positive, ranging from 6.41 for cookies to 11.59 for bow tie cookies, and all values of parameter b* were positive as well, ranging from 25.62 for jam-filled puff pastry to 31.98 for bow tie cookies (Table 4). By totally replacing conventional fats with oleogel, brightness (L*) and the parameters a* and b* were reduced in almost all of the analyzed samples. Therefore, for oleogel products, the highest value of the brightness index, was recorded for apple pie (L*-68.09), followed by jam-filled puff pastry (L*-66.95), cookies (L*-63.84), cheese crackers (L*-62.24) and bow tie cookies (L*-59.01). Also, products formulated with oleogel can be characterized by a shade of red (a*) from 5.46 for cookies to 8.51 for bow tie cookies, and yellow (b*) from 26.23 for apple pie to 27.91 for cheese crackers. These values are similar to those obtained by Tanislav et al. [58] for oleogel biscuits. Higher values of the parameters L*, a* and b* of the surface of the biscuits formulated with shortening compared to those formulated with different types of natural waxes (candelilla wax, rice bran wax, white beeswax, yellow beeswax) were reported by Onacik-Gur and Zbikowska [9] and ∆E values ranged from 2.55 to 3.06. Zhao et al. [51] observed a few differences between the color parameters of oleogel cookies and conventional ones, but the values were comparable between 62.88 and 67.35 for L*, 10.22 and 12.77 for a*, and 31.68 and 34.99 for b*. Instead, Yilmaz and Ogutcu [30] reported negative values of the parameter a* for the surface of conventional and oleogel cookies, with values between 0.04 and 0.41, suggesting that they showed slightly green tones, and the cookies formulated with oleogel showed lower values of the brightness (L* -79.34–81.77) and higher of the spectrum b* (32.91–33.55) compared to the conventional sample (L* -84.13 and b*- 28.97). In addition to the method used, the raw materials incorporated and every stage of the technological process, particularly the parameters and duration of baking, affect the color of the products. Compared to the visible difference between the fats (from 28.19 to 48.36), the differences were smaller for the doughs (from 2.13 to 21.93) and, respectively, for the finished products, the biggest difference being for cookies (12.68) and the lowest, almost undetectable with the human eye, for jam-filled puff pastry (4.05).

Fat losses

Replacing solid fats with structured oils can increase oil migration to the product surface [52]. The fat losses of conventional and oleogel products were analyzed on day 1, 9 and 14 of storage, at ambient temperature, to determine their physical stability. Pastry products are formulated with a high fat content, so they have a higher risk of exudation and migration of the lipid phase to the product surface, which can affect the sensory properties, oxidative stability during storage, and ultimately result in a decrease of product quality [9, 61]. Fat migration is associated with the formation of an oil layer on the surface of the product [9]. For the finished products, the highest amount of exuded oil was identified on day 9, values that remained constant or in some cases slightly increased until day 14 of storage. For conventional products, on the first day, the apple pie and jam-filled puff pastry did not show fat losses, and for the other samples the losses were between 0.33 g/100 g for cookies and 0.54 g/100 g for bow tie cookies (Table 4). On the other hand, fat loss values increased beginning on day 9 and reached the maximum on the day 14, with values between 0.46 g/100 g for jam-filled puff pastry and 4.05 g/100 g for cheese crackers. These values are similar to those obtained by Msaddak et al. [61], during the 30 days of storage (ambient temperature) for cookies formulated with butter, where a maximum of 3.39% oil losses were recorded. In the case of oleogel products, higher fat losses were observed during the 14 days of analysis, compared to conventional products but only significant in the case of jam-filled puff pastry. For the apple pie, cookies and jam-filled puff pastry, on day 1, the fat losses 0.18, 0.31 and 0.33 g/100 g finished products, while higher losses were registered for cheese crackers—1.74 g/100 g and bow tie cookies—3.29 g/100 g. An increase in the amount of oil loss in biscuits stored for 24 h in a thermostat at 30 ℃ was observed in the study by Onacik-Gur and Zbikowska [9]. Biscuits obtained with oleogels from rapeseed oil and 2% rice bran wax recorded a loss of 0.17 g and those with 5% white or yellow beeswax of 0.23 g and 0.25 g respectively. These were compared with samples obtained with palm oil whose loss was 0.16 g. In contrast, Giacomozzi et al. [52] on both day 7 and day 10 of analysis observed that muffins formulated with commercial margarine or high oleic sunflower oil, showed higher oil losses (< 0.8 g/100 g) compared to oleogels formulated with monoglyceride, which exhibited approximately 50% lower lipid phase migration. Thus, in addition to the type of fat (naturally saturated or unsaturated), the type of structuring agent can influence the migration capacity of the lipid phase. In our study, on day 14, the highest oil losses were recorded for oleogel cheese crackers—4.49 g/100 g and oleogel bow tie cookies—4.88 g/100 g. These increased oil exudations corresponded to those observed visually, as the products presented a slightly oily appearance. Cheese crackers and bow tie cookies formulated with conventional fat or oleogel, showed the highest amount of oil losses during the 14 days of analysis, while the samples of conventional jam-filled puff pastry (0.46 g/100 g) and apple pie (0.63 g/100 g) recorded the lowest values. Consequently, pastries formulated with conventional fats have better physical stability compared to products formulated with oleogel. The higher losses of the lipid phase in reformulated products may be related to changes that occur during the baking process when the oleogel destabilizes its structure, which is then reconstituted (due to its thermoreversible property) by cooling and storage at the ambient temperature, but not as initially due to the interaction with the raw materials from the finished product.

Saturated fat decrease

The total replacement of conventional fats with oleogel contributed to the reduction of saturated fats in the composition of pastry products, indicating a significant nutritional improvement. The use of oleogel prepared from refined sunflower oil (89% unsaturated fatty acids) contributes to an increase in unsaturated fatty acids while decreasing saturated fatty acids. The replacement of margarine and lard with oleogel reduced the content of saturated fatty acids by 73.92% in cheese crackers and by 70.88% in apple pie. The substitution of commercial margarine and puff pastry margarine in the jam-filled puff pastry decreased the total quantity of saturated fatty acids by 72.95%. The replacement of butter in the case of cookies resulted in the highest reduction in the amount of saturated fatty acids- 80.86%. Among all products, the replacement of commercial margarine in the composition of the bow tie cookies led to the lowest reduction in saturated fatty acids—67.56% (Online Resource Fig. S5).

Conclusions

The use of oleogel allowed the complete replacement of conventional fats in the production of tender pastries (bow tie cookies, cheese crackers, apple pie, cookies) and puff pastry (jam-filled puff pastry). The textural properties of oleogel were significantly different from those of puff margarine, but comparable to those of commercial margarine, mixture of margarine and lard, and butter. All the analyzed fats belong rheologically to the viscoelastic solids, and the oleogel showed the strongest gel network compared to the conventional fats. Both conventional fat and oleogel doughs showed more prominent elastic properties than viscous ones (Gʹ > G″). Regarding the textural profile for the finished products, the prototypes formulated with oleogel showed lower hardness values, which indicates the higher tenderizing effect imprinted by liquid oil from the composition of oleogels. The lipid losses determined during 14 days of analysis indicated a decrease in the physical stability of doughs and oleogel products, which may be attributable to changes that occur during baking when the oleogel destabilizes its structure. The use of oleogel has resulted in the production of pastries with properties comparable to those of conventional products, and, in terms of structural properties, the substitution of conventional lipids with oleogel was more suitable for cookies. For the other products, rolling and fermentation operations raised problems in the production process, by obtaining products with a lower volume. The color difference between the conventional and oleogel products was higher than 3, and the largest difference (12.68) was identified for bow tie cookies. Using oleogel in pastries, a nutritional improvement would be achieved, by increasing the content of unsaturated fatty acids, while decreasing the amount of saturated fatty acids by up to 80.86% (for cookies). It is recommended in the future to perform a sensory analysis to determine the acceptability of products by consumers, and to perform oxidative studies to determine the shelf life of pastries.