Oil-Structuring Characterization of Natural Waxes in Canola Oil Oleogels: Rheological, Thermal, and Oxidative Properties

Appl Biol Chem (2017) 60(1):17–22 Online ISSN 2468-0842 DOI 10.1007/s13765-016-0243-y Print ISSN 2468-0834

ARTICLE

Oil-structuring characterization of natural waxes in canola oil oleogels: rheological, thermal, and oxidative properties

Jeongtaek Lim1 . Hong-Sik Hwang2 . Suyong Lee1

Received: 25 October 2016 / Accepted: 2 December 2016 / Published online: 20 December 2016 Ó The Korean Society for Applied Biological Chemistry 2016

Abstract Natural waxes (candelilla, carnauba, and bees- Keywords Natural wax Á Oleogel Á Organogelator Á wax) were utilized as canola oil structurants to produce Texture Á Thermo-rheology oleogels. Physicochemical properties of the oleogels were evaluated from textural, thermo-rheological, and oxidative points of view. The oleogels with candelilla wax exhibited the highest hardness, followed by carnauba and beeswax Introduction oleogels, while the most adhesive and cohesive properties were observed in the beeswax oleogel. The flow behaviors Edible vegetable oils are well-recognized to contain a of the oleogels over temperature exhibited greater sensi- variety of health-functional components, such as unsatu- tivity of carnauba wax oleogels to temperature. The storage rated fatty acids, compared to solid fats of animal origin. moduli of the oleogels were more temperature-dependent, However, the edible oils that are generally in a liquid state causing the crossover of the storage and loss moduli during at room temperature lack the physical functionalities suit- the temperature change. Highly linear correlations able for the texture and stability of food products. Liquid (R2 [ 0.96) were observed in the log plots of solid fat oils are chemically or enzymatically converted into semi- content and rheological property. In addition, the lowest solid or plastic fats to produce shortening and margarine peroxide values were observed in the candelilla wax (Ghosh 1996). However, there still exist health-related oleogels, followed by the carnauba and beeswax oleogels, concerns such as the increased amount of saturated fatty demonstrating that oleogels with a harder texture exhibited acids and generation of trans fatty acids. greater resistance to oxidation during storage. As a novel structuring method for edible oil, organogelation has recently received much attention in the food and pharmaceutical industry. Through this organogelation, edible oils are entrapped within a thermo-reversible and three-di- Mention of trade names or commercial products in this article is solely for the purpose of providing scientific information and does not mensional network derived from organogelators. Thereby, imply recommendation or endorsement by the U.S. Department of the liquid oils are physically solidified without changing their Agriculture. USDA is an equal opportunity provider and employer. chemical compositions, producing oleogels also called organogels (Vintiloiu and Leroux 2008). These oleogels have & Suyong Lee been shown to have great potential as alternatives to solid fats [email protected] in specific food applications such as baked goods (Jang et al. 1 Department of Food Science & Technology and 2015;Yılmaz and O¨ g˘u¨tcu¨ 2015) and ice cream (Zulim Carbohydrate Bioproduct Research Center, Sejong Botega et al. 2013). However, it is a challenge to explore University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, suitable oleogels that can provide a similar level of perfor- Republic of Korea mance without organoleptic changes. 2 United States Department of Agriculture, Agricultural Since oleogels are biphasic systems consisting of Research Service, National Center for Agricultural Utilization Research, Functional Foods Research, Peoria, IL, organogelators and edible oil, the physical characteristics of USA the oleogels vary depending on the type and concentration 123 18 Appl Biol Chem (2017) 60(1):17–22 of the organogelators used. Out of various organogelators, Textural measurement waxes that are a mixture of more or less hydrophobic organic substances of medium chain length (Endlein and In order to investigate the textural properties of the oleogel Peleikis 2011) exist in form of natural substances and are re- samples, texture profile analysis was conducted using a texture obtained in a sustainable cycle. Furthermore, natural waxes analyzer (TMS-Pro; Food Technology Co., Sterling, VA, can be considered as promising candidates for food appli- USA) with a 100 N load cell. For doing so, the cylindrical- cations because they are FDA-approved as food additives shaped oleogel samples were prepared with a mold (25 mm (FDA 2015). In preceding studies, several natural waxes diameter, 10 mm height). The oleogels were placed on the were combined with vegetable edible oils to produce oleo- platform of the texture analyzer and then compressed two gels. Candelilla and carnauba waxes were applied to saf- times to 30% of the original height by using a cylindrical probe flower and virgin olive oils, respectively (Toro-Vazquez (5 cm diameter) at a speed of 10 mm/min. Textural parame- et al. 2007;O¨ gˇu¨tcu¨ and Yılmaz 2014). Soybean oil oleogels ters (hardness, adhesiveness, cohesiveness, gumminess) were were prepared with sugarcane, candelilla, and sunflower measured from the force versus time curves obtained. waxes and their thermal and optical properties were char- acterized (Rocha et al. 2013; Hwang et al. 2015). In addi- Rheological measurements tion, sunflower oil-rice bran wax oleogels were prepared to replace solid fat in ice cream (Zulim Botega et al. 2013) and The rheological properties of oleogels (shear viscosity and rapeseed oil was structured with shellac wax for several dynamic viscoelasticity) were investigated as a function of food applications such as spreads, chocolate pastes, and temperature by using a controlled-stress rheometer cakes (Patel et al. 2014). However, the physicochemical (AR1500ex, TA Instruments, New Castle, DE, USA) with properties of oleogels have not been extensively compared, a 40-mm parallel plate. The melted oleogels were placed depending on the types of natural wax and vegetable oil. on the peltier plate of the rheometer and their viscosities Furthermore, research focuses have not been placed on the were measured at a shear rate of 100/s by increasing correlation between the textural/rheological properties of temperature from 50 to 90 °C at a heating rate of 2 °C/min. oleogels and their oxidative stability that is a critical attri- In the case of the dynamic viscoelasticity, dynamic tem- bute of oil-based food products with regard to quality perature ramp tests from 25 to 80 °Cat2°C/min were attributes. carried out at a frequency of 1 Hz and a 0.01% strain, Canola oil is known to be higher in unsaturated fatty which was within the linear viscoelastic limit. acids than other vegetable oils (Kim et al. 2010). There- fore, the oleogels prepared with canola oil have a high level Determination of solid fat content of unsaturated fatty acids while they may be more vul- nerable to oxidation during storage. Thus, in this study, The solid fat content (SFC) of oleogels was measured in canola oil oleogels were prepared with three different the temperature range from 10 to 85 °C using an Mq-one natural waxes—candelilla, carnauba, and beeswax. Their SFC Analyzer (Bruker, Ettlingen, Germany). The oleogels physicochemical characteristics were then evaluated in were melted at 90 °C for 30 min, poured into NMR glass terms of textural, thermo-rheological, and oxidative tubes, and placed at 0 °C for 60 min. They were then held properties. at each measuring temperature for 30 min prior to SFC measurement.

Thermal analysis Materials and methods Differential scanning calorimetry (DSC 200 F3 Maia, Preparation of oleogels NETZSCH, Bavaria, Germany) was used to investigate the thermal properties of oleogels. The oleogels (10–15 mg) Candelilla wax (Kahl GmbH & Co. KG, Trittau, Germany), were weighed into stainless steel pans that were hermeti- carnauba wax (Starlight Co., Fortaleza, Brazil), and bees- cally sealed. The sample was heated from 25 to 90 °C, and wax (Hooper pharm GmbH Co., Hamburg, Germany) were then cooled to -20 °C, and heated again to 100 °C at a rate obtained from commercial sources and canola oil was of 10 °C/min and the empty pan was used as reference. provided from CJ Co. (Seoul, Korea). In order to prepare oleogels, canola oil was heated and each wax was slowly Peroxide value measurement added (10% w/w) with continuous agitation until completely dissolved, followed by cooling at room temperature The effect of natural waxes on the oxidative stability of overnight. oleogels was investigated by measuring their peroxide 123 Appl Biol Chem (2017) 60(1):17–22 19 values during 18-day storage under the accelerated condi- with rice bran, carnauba, and candellila waxes (Das- tions (60 °C). Based on the method of Cho and Lee (2015), sanayake et al. 2009). In addition, the beeswax oleogels the peroxide values of the oleogel samples were periodi- were the most adhesive and cohesive, while the lowest cally measured and expressed as miliequivalents of active values were observed in the candelilla wax samples. In the oxygen per kilogram of oil (meqO2/kg). case of gumminess (hardness 9 cohesiveness), the candelilla wax oleogels exhibited greater gumminess than the Statistical analysis other samples due to their hard texture. Thus, canola oil seemed to pack more tightly within the gel network derived All measurements were made in triplicate and the SAS from candelilla wax, producing oleogels with a harder program (SAS Institute Inc., Cary, NC, USA) was used for texture. statistical analysis of experimental data. The signiﬁcant The viscosities of oleogels were monitored as a function difference among samples was examined from analysis of temperature ranging from 50 to 90 °C and their viscosity variance (ANOVA), followed by Duncan’s multiple range dependences on the temperature were investigated test for mean comparisons at a conﬁdence level of 95%. according to the following Arrhenius model (Jang et al. 2015):

g ¼ A Á expðEa=RTÞ; Results and discussion where g is the oil viscosity, A is the pre-exponential factor, The visual appearances of canola oil oleogels with natural Ea is the activation energy, R is the gas constant, and T is waxes are shown in Fig. 1. Liquid canola oil was suc- the absolute temperature. 2 cessfully structured into solid-like oleogels using natural A high coefficient of determination (R [ 0.97) as waxes (candelilla wax, carnauba wax, and beeswax) as shown in Table 2 suggested that the viscosity plots against oleogelators. temperature were well fitted by the Arrhenius equation. The textural properties of the oleogels were investigated The activation energy (Ea) in the Arrhenius equation is by using texture profile analysis. As shown in Table 1, the proportional to the slope of the Ln (viscosity) versus highest value of hardness, that is the maximum force 1/temperature plot. Higher Ea indicates that the curve slope during the first compression, was observed in the oleogels becomes steeper, suggesting that Ea can provide a good with candelilla wax, followed by carnauba wax and bees- approximation to the rheological sensitivity of oleogels to wax oleogels. This result was in agreement with the pre- temperature. As also shown in Table 2, the highest value of ceding study where the penetration depth measurement was Ea was observed in the carnauba wax oleogels, followed by made to compare the hardness of the oleogels prepared candelilla wax and beeswax oleogel samples. Thus, among the samples examined, the beeswax oleogels had a small change in viscosity with increasing temperature. The effects of temperature on the viscoelastic properties of oleogels were investigated in the temperature range from 25 to 80 °C. As shown in Fig. 2, all the samples exhibited higher values of G0 (storage modulus) than those of G00 (loss modulus) at low temperatures, showing a dominant elastic property (solid-like state). It was interesting that the G0 and G00 of the candelilla wax oleogels remained constant within the range of temperature lower than 40 °C. How- ever, the two parameters of the oleogels with carnauba wax and beeswax continued to decrease with increasing temperature. Upon further heating, two viscoelastic parameters Fig. 1 Visual appearance of canola oil oleogels with natural waxes decreased with more temperature dependence of the G0,

Table 1 Textural properties of Candelilla wax Carnauba wax Beeswax oleogels prepared with natural waxes (Means with different Hardness (N) 25.12 ± 2.05a 10.43 ± 0.13b 5.46 ± 0.28c letters in the same row differ Adhesiveness (NÁs) 1.97 ± 0.14c 2.95 ± 0.24b 4.74 ± 0.52a signiﬁcantly at p \ 0.05) Cohesiveness 0.14 ± 0.02c 0.20 ± 0.01b 0.33 ± 0.02a Gumminess (N) 3.51 ± 0.65a 2.03 ± 0.05b 1.79 ± 0.12b

123 20 Appl Biol Chem (2017) 60(1):17–22

Table 2 Arrhenius model parameters of oleogels prepared with natural waxes (Means with different letters in the same column differ significantly at p \ 0.05)

2 Ea (J/KgÁmol) A (PaÁs) R

Candelilla wax 4.97E?07 ± 1.20E?06b 1.02E-09 ± 4.19E-10b 0.9831 Carnauba wax 8.00E?07 ± 3.51E?05a 4.47E-14 ± 6.25E-15b 0.9787 Beeswax 2.10E?07 ± 5.87E?05b 1.42E–05 ± 2.83E-06a 0.9683 leading to the crossover of the G0 and G00 curves at tem- The effect of natural waxes on the SFC of canola oil peratures of 64, 74, and 46 °C for candelilla, carnauba, and oleogels was investigated as a function of temperature. As beeswax oleogels, respectively. Thereby, the G00 became shown in Fig. 3(A), the SFC profiles were distinctly dif- greater than the G’ at high temperatures. ferent from each other. These results indicated that the SFC of the oleogels was significantly affected by the type of natural waxes. Sharp decreases in the SFC were present in the temperature range of 50–80, 35–70, and 20–55 °C for carnauba, candelilla, and beeswax, respectively. Thus, it appeared that the SFC of the carnauba oleogels remained constant at the temperature close to body temperature among the oleogel samples. The crystalline phase of the carnauba oleogels was completely melted at the highest temperature (80 °C), followed by candelilla wax (70 °C) and beeswax (55 °C). This trend was in great accordance with the viscoelastic changes over temperature (Fig. 2). As shown in Fig. 3(B), highly linear lines (R2 [ 0.96) were well fitted to the log plots of SFC and viscoelastic property

Fig. 2 Changes in the viscoelastic properties of natural wax-incor- Fig. 3 Solid fat content of natural wax-incorporated oleogels (A) and porated oleogels over temperature correlation between solid fat content and rheological property (B) 123 Appl Biol Chem (2017) 60(1):17–22 21

Fig. 5 Effect of natural waxes on the peroxide value of oleogels under accelerated storage conditions Fig. 4 DSC thermograms of oleogels prepared with natural waxes during storage was assessed under the accelerated condi- (G0), suggesting that the solid fat of the oleogels con- tions (60 °C) and compared with that of fresh oil without tributed to their elastic property. organogelators. It was noted that all the oleogel samples The thermal properties of candelilla, carnauba, and exhibited higher peroxide values than the fresh oil before beeswax oleogels were investigated as shown in Fig. 4. the storage experiment started (Fig. 5). It could be There were heat-absorbing peaks distinctly seen in the explained by the fact that the oils in the oleogels were DSC thermograms. Two separate peaks at around exposed to high temperature conditions during the oleogel 20–50 °C were observed in the melting thermogram of the preparation. As also shown in Fig. 5, the peroxide values of oleogels made up with beeswax as an organogelator, all the samples had a tendency to gradually increase with implying the heterogeneous nature of the oleogel matrix. increasing storage time. It was interesting that the peroxide On the other hand, an intense melting peak was evident in value of the fresh oil significantly increased at a faster rate the temperature range from 40 to 60 °C and from 60 to during storage, compared to the oleogels. Furthermore, the 80 °C for the candelilla and carnauba wax oleogels, increasing trends of the peroxide values were distinctly respectively. These melting patterns of the oleogel samples different depending on the type of natural waxes used in were in great agreement with their rheological changes and this study. Specifically, the lowest peroxide values were SFC over temperature (Figs. 2, 3(A)). These melting observed in the candelilla wax oleogels, followed by the properties could be favorably compared with the results carnauba wax and beeswax oleogels. Interestingly, these reported in the preceding studies (Rocha et al. 2013; peroxide value patterns correlated with the hardness of the O¨ gˇu¨tcu¨ and Yılmaz 2014). The melting enthalpy values of oleogels (Table 1). That is, the harder the oleogels became, the candelilla and carnauba oleogels were determined to be the lower peroxide value they had. This suggested that the about 7.8 and 12.5 J/g, respectively. It suggested that restriction of oil mobility and migration via organogelation higher energy was needed to melt the carnauba oleogels, were effective in retarding the oil oxidation during storage. compared to the candelilla oleogels. Three different natural waxes (candelilla, carnauba, and Oleogels are typically prepared by mixing oil and beeswax) were combined with canola oil to produce organogelator with continuous agitation at high tempera- oleogels, and their oil-structuring characteristics were ture, which may play a negative role in the oxidation of oils evaluated in terms of textural, thermo-rheological, and in the oleogels. Yilmaz and O¨ gˇu¨tcu¨ (2014) reported that the oxidative properties. The use of candelilla wax produced higher peroxide values were observed in the hazelnut oleogel samples with a harder texture that seemed to be oleogels with beeswax when they were stored at room effective in retarding the oil oxidation during storage. The temperature rather than refrigerator temperature. In addi- beeswax oleogels were also shown to be less sensitive to tion, the effect of ethylcellulose on the oxidative stability temperature change. The viscoelastic patterns of the natural of oleogels was evaluated that was dependent on treatment wax-incorporated oleogels over temperature were in good time/temperature and concentration of ethylcellulose (Kim agreement with their SFC and DSC results. Thus, the et al. 2014). However, preceding studies on the oxidation results of this study provided fundamental information on of oleogels prepared with different organogelators have the physicochemical properties of oleogels prepared with been very limited in the literature. Therefore, the effect of natural waxes. Since current consumer demands have different organogelators on the peroxide values of oleogels moved to foods that are naturally beneficial to their health

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