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Food Chemistry
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E
ffect of different microwave power setting on quality of chia seed oil
obtained in a cold press
Mehmet Musa Özcan
a,⁎, Fahad Y. Al-Juhaimi
b, Isam A. Mohamed Ahmed
b,⁎, Magdi A. Osman
b,
Mustafa A. Gassem
baDepartment of Food Engineering, Faculty of Agriculture, University of Selçuk, 42031 Konya, Turkey
bDepartment of Food Science & Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh, Saudi Arabia
A R T I C L E I N F O Keywords:
Chia seed oil Microwave heating Physico-chemical properties Total phenol
Antioxidant activity Fatty acid composition Tocopherol Phenolic compounds
A B S T R A C T
This study was conducted to investigate the impacts of microwave heating treatments at different powers (0, 180, 360, 540, 720 and 900Watts) on the quality attributes of chia seed oil. Linoleic acid contents of the chia seed oil heated in microwave oven changed between 19.21% (900 W) and 21.17% (control), respectively (p < 0.05). Linolenic acid contents of heated chia seed oils varied between 66.84% (900 W) and 68.71% (control).α-Tocopherol and β-tocopherol contents of the chia oil samples varied between 47.71 mg/100 g (900 W) and 51.17 mg/100 g (control) to 62.58 mg/100 g (900 W) and 67.81 mg/100 g (control), respectively. While caffeic acid contents of the oils change between 0.27 mg/g (900 W) and 3.84 mg/g (control), rosmarinic acid contents of chia seed oils were found between 1.32 mg/g (900 W) and 3.17 mg/g (control). Results reflect a change in the chemical structures of the chia oil. Overall, much care should be taken when roasting chia seeds in microwave to avoid lossess in the bioactive components of chia oil.
1. Introduction
Chia (Salvia hispanica L.; Lamiaceae family) is a herbaceous plant in nature and grown semi-annually. The oil content of chia seed varied between 25 and 35% and the majority of the fatty acids present in chia seed oil are polyunsaturated fatty acids, withα-linolenic acid or omega-3 accounting for about 68% of the polyunsaturated fatty acids (Borneo, Aguirre, & León, 2010; Ayerza & Coates, 2011). Microwave heating is one of the main processing operations applied to edible seeds and nuts and it can cause various physico-chemical changes. The roasting con-ditions can cause significant changes in physico-chemical properties such as color,flavor, fatty acid profile and bioactive compounds of oil kernel and seed (Cerretani, Bendini, Rodeiguez-Estrada, Vittadini, & Chiavaro, 2009). During microwave heating, different chemical reac-tions may occur that determine the quality and safety of the oil. During this reaction, some components may become damaged while others may become harmful. The basic classic degradation patterns seen in oils include hydrolysis, oxidation and thermal polymerization (Albi, Guinda, Pérez-Camino, & León et al., 1997a). Several studies were conducted on the effects of microwave heating on food and constituents like lipid fractions (tocopherol, fatty acids) of oils (Albi, Lanzón, Guinda, Léon, & Pérez-Camino et al., 1997b; Brenes, García,
Dobarganes, Velasco, & Romero, 2002; Hassanein, Shami, & El-Mallah, 2003; Cerretani et al., 2009).Brenes et al. (2002)applied mi-crowave heating treatment (500 W for 5 and 10 min) for olive oil ob-tained from Picual and Arbequina olive varieties, and they identified phenolic components. Under these conditions, they observed that the phenolic components of both olive oils were affected by microwave radiation. Fatty acids are the key components of the saponifiable frac-tion of oils. Several studies have investigated the effect of microwave heating on quality of vegetable oils (Albi et al., 1997a; Caponio, Pasqualone, & Gomes, 2003). Tocopherols and tocotrienols are natural lipophilic antioxidants that prevent autoxidation in fats and oils. To-copherols contributed to the nutritional values of foods and are con-sidered as components of vegetable oils (Cerretani et al., 2009). Bioactive compounds including quercetin, kaempherol, catechin, caf-feic, vanillic and chlorogenic acids have also been identified in chia seed and oils (Ixtaina et al., 2011; da Silva Marineli, Moraes, Lenquiste, Godoy). However information ragarding microwave heating and its impact on the tocopherol contents, fatty acid compositions, phenolic compounds of chia seed oil are scarce. Therefore, the aim of this study was to determine the effect of microwave heating treatments at dif-ferent power on physico-chemical properties, total phenol, antioxidant activity, fatty acid composition, tocopherol contents and phenolic
https://doi.org/10.1016/j.foodchem.2018.11.048
Received 22 August 2018; Received in revised form 9 November 2018; Accepted 9 November 2018
⁎Corresponding authors.
E-mail addresses:[email protected](M. Musa Özcan),[email protected](I.A. Mohamed Ahmed).
Available online 10 November 2018
0308-8146/ © 2018 Published by Elsevier Ltd.
compounds of chia seed oils obtained by cold pressing.
2. Materials and methods
2.1. Materials
Chia seeds were purchased from the local market at Konya city, Turkey. The seeds were cleaned by removing dust, stones and plant debris, and sieved to remove all types of impurities. The seeds were then packed in air tight polypropylene bags and stored in refrigerator till further used.
2.2. Methods
2.2.1. Microwave heating
Each seed sample (100 g) was separately roasted in a microwave oven at 180, 360, 540, 720 and 900 W Powers for 15 min. Microwave applications were performed at the Arçelik ARMD 580 (Istanbul, Turkey) factory, using an ARÇELIK microwave device with a micro-wave frequency of 2450 MHz. The dimensions of the micromicro-wave cavity were 34.5 × 34.0 × 22.5 cm. Chia seeds for each treatment were placed into glass plate with 50 ml capacity, and then heated in micro-wave oven at 180 W, 360 W, 540 W, 720 W and 900 W at 2450 MHz for 15 min. Chia samples were cooled in a desiccator, and kept at−25 °C under nitrogen in sealed bottles. Moisture contents of seeds heated separately in Microwave oven for 180, 350, 540, 720 and 900 W mi-crowave powers were 10.3, 9.6, 8.4, 6.1 and 4.9%. The moisture con-tent of control group without treatment is 11.8%. Then, the seeds were milled using a laboratory scale hammer mill before analysis and the resulting powder was sieved through a 60 mesh screen until fine powder was obtained (Cissouma, Tounkara, Nikoo, Yang, & Xu, 2013).
2.2.2. Cold press
Oil was extracted using cold press method from chia seeds. Cold press extraction was done for both roasted and unroasted seeds. After extraction, the oils were kept sedimentation in order to remove solid impurities for one week. The oil wasfiltered and kept in sealed dark coloured bottles under nitrogen at 4 °C.
2.2.3. Physico-chemical properties
The acidy, peroxide value, viscosity, saponifiable and unsaponifi-able values for chia seed oil samples were determined according to Standard AOAC (1990)methods. Wax precipitation was carried out using a procedure as proposed byBurger, Perkins and Striegler (1981).
2.2.4. Extraction of phenolics and antioxidants
The phenolic contents and antioxidant values of extracts were car-ried out using the extraction method as reported by Talhaoui et al. (2014). About 4 ml chia seed oil was mixed with 20 ml of methanol followed by 15 min sonication and 10 min centrifugation at 5000 rpm. The extraction was carried out in two cycles and supernatants were separated and concentrated at 37 °C in a rotary evaporator under va-cuum. The extracts volume was made up to 25 ml using methanol.
2.2.5. Total phenol
The phenolic content of the chia oil extract was quantified with spectrophotometer (absorbance at 765 nm) by using Folin-Ciocalteau reagent (FCR) as described by Madaan, Bansal, Kumar & Sharma (2011). Gallic acid standard curve was constructed and used to evaluate the total phenolic, which was expressed as gallic acid equivalent. The samples and standard mixtures prepared in the same manner were vortexed and allowed to stand at room temperature for 30 min, after which the optical activity at 765 nm was measured using UV/VIS spectrophotometer (Schimadzu, Japan) using distilled water as a blank.
2.2.6. Antioxidant activity
Antioxidant activity of oil extraxt was determined by using the method described byLee et al. (1998). DPPH solution of methanolic acid was used for the assessment of antioxidant activity of the samples. About 1 ml extract was added to 2 ml methanolic solution of DPPH followed by vigorous shaking. The mixture was then incubated for 30 min at 37 °C. The extract wasfiltered and concentrated by rotary evaporator. The procedure was repeated for each sample, and 0.5 ml of sample solution was added to 1 ml of DPPH solution separately. The absorbance was recorded at 517 nm by using a spectrophotometer. The DPPH scavenging capacity was calculated as the following:
= − ×
Inhibition (%) (Acontrol Asample)/Acontrol 100
where: Asample was the absorbance of samples, and Acontrol was the
absorbance of methanolic DPPH solution.
2.2.7. Determination of phenolic compounds
The analysis for individual phenolic compounds in the extracts from chia seed oil was carried out using Shimadzu-HPLC equipped with PDA detector and Inertsil ODS-3 (5 µm; 4.6 × 250 mm) column. The mobile phase consisted of 0.05% acetic acid in water (A) and acetonitrile (B) and aflow rate was set at 1 ml/min whereas injection volume was 20 µL at 30 °C. The peaks were recorded at 330 nm and sample was run for 60 min.
2.2.8. Fatty acid composition
Chia seed oil was esterifited following theISO-5509 (1978) proce-dure using gas chromatography machine and the identification of fatty acid methyl esters was done through the comparison of the retention time for samples and standards. The samples were injected into a gas chromatography system (Shimadzu GC-2010) equipped with a capillary column (Tecnocroma TR-CN100, 60 m × 0.25 mm, film thickness: 0.20 µm) andflame-ionization detector (FID). The injection block and detector temperature was set at 260 °C and nitrogen was used as a mobile phase at aflow rate of 1.51 ml/min. The total flow rate was 80 ml/min whereas the split rate was 1/40. Column temperature was set as 120 °C for 5 min followed by an increment of 4 °C/min until reached 240 °C where it was held for 25 min.
2.2.9. Tocopherol content
A 20μL sample was instantaneously injected into the Diol phase HPLC column 25 cm × 4.6 mm ID (Merck, Darmstadt, Germany) at 1.3 ml/min flow rate. The contents of tocopherol in the oil samples were determined following method ofSpika et al., (2015). HPLC system for tocopherol analysis consisted of Shimadzu-HPLC equipped with PDA detector and LiChroCART Silica 60 (4.6 × 250 mm, 5 µ; Merck, Darmstadt, Germany) column. Standard solutions of tocopherols (α, β, γ and δ-tocopherol) were used at 0–100 mg/L concentrations for com-parison and quantification.
2.3. Statistical analyses
All analytical measurements were carried out in triplicate. The ob-tained data were analyzed using analysis of variance (JMP version 9.0, SAS Inst. Inc., Cary, N.C., U.S.A). The results were expressed as means ± standard deviation of independent microwave powers and chia seed oil samples (Püskülcü &İkiz, 1989). The correlation coeffi-cients among the physico-chemical quality parameters were assessed using the means values of different treatments by using Stat View software and significance was accepted at *
p < 0.05; **p < 0.01;
***p < 0.001.
3. Results and discussion
Table 1illustrates acidity, peroxide value, density, viscosity, sapo-nification value, unsaponifiable matter, total phenolics, antioxidant
activity, total wax, fatty acid composition, tocopherol contents and phenolic compounds of chia oil extracted from chia seeds roasted at different microwave powers. While acidity values of chia oils change between 0.34 mg KOH/g (control) and 23.58 mg KOH/g (900 W), per-oxide values of the oil extracted from chia seed roasted by microwave heating exposure at different power setting varied between 1.17 meq O2/kg (control) and 27.46 meq O2/kg (900 W). While saponification
values of chia oils heated in microwave change between 215.03 mg KOH/g (900 W) and 218.03 mg KOH/g ((180 W), unsaponifiable matter values of heated oils varied between 0.661% (900 W) and 0.724% (180 W). Both saponification and unsaponifiable matter values of con-trol groups were found higher compared to oils heated in different powers in microwave oven. In addition, total phenol contents of chia oils heated by microwave oven are determined between 0.55 mg GAE/g (900 W) and 0.91 mg GAE/g (control), whereas antioxidant activity values were changed between 0.38% (900 W) and 0.72% (control). It is thought that antioxidant activity and total phenol values are decreased from the decomposition of phenolic compounds at high microwave powers. Also, total wax contents of chia oils were found between 57.17 mg/kg (900 W) and 112.74 mg/kg (control). Total wax contents of chia oil heated in different microwave powers decreased compared to control results of chia oil. The highest and lowest wax contents were found in oil heated at 180 and 900 W. Viscosity values of oil samples changed between 0.17 mPa.s (control) and 11.59 mPa (900 W). The results showed that microwave heating produce losses in the quality of the oil. Acidity, peroxide and viscosity values of the oil samples exposed to microwave heating were the most affected properties compared to control samples (oils extracted from unroased seeds), and followed by total phenolics, antioxidant activity, and total wax. The initial free acidity of vegetable oils is an important parameter affecting the thermal performance of the oil. The results of the studies made have been found to cause a partial increase in the amount of free fatty acids in micro-wave heating. The micromicro-wave heating time probably promoted the occurrence of hydrolysis in the samples since changes in acidity values were found. Increasing of total acidity may be due to decomposition of some phospholipids and triacylglycerols to glycerol and free fatty acids. Oils with a high degree of unsaturation are most susceptible to auto-xidation. Generally, increasing of the peroxide value is proportional to the heating time. High peroxide values are a definite indication of a rancid fat, but moderate values may be the result of depletion of per-oxides after reaching high concentrations. The correlation coefficients among the physico-chemical quality parameters were assessed using the means values of different treatments using Stat View software and significance was accepted at *p < 0.05; **p < 0.01; ***p < 0.001
(Table 2). The results of the studies made have been found to cause a partial increase in the amount of free fatty acids following microwave heating. Cerretani et al. (2009) reported that they heated the extra virgin olive oil to 720 W for 12 min and found a significant increase in the free acidity value. In other study, peroxide value in the oil extracted from grape seeds dried by microwave when compared with air dried
ones increased (Oomah, Liang, Godfrey, & Mazza, 1998).Caponio et al. (2003)compared the peroxide values of olive oil, sunflower and peanut oil, and reported higher peroxide values for peanut and sunflower when compared to olive oil. When oils are exposed to microwave energy without any temperature increase, the results obtained are similar and as a result microwave energy alone is not sufficient to cause viscosity and density increase in itself (Albi et al., 1997a). Viscosity and density increase with increasing temperature, and are directly proportional to the chemical reactions that occur in the oil. The formation of cyclic monomers, dimmers and polymers in a non-radical mechanism cause the increasing of viscosity in vegetable oils. The formation of con-jugated dienes is related to the double bonds migration within the unsaturated fatty acids.Ayerza (2013)reported that peroxide values of Tzotzol and Iztac chia oils were determined as 0.61 meq O2/kg and
0.82 meq O2/kg, respectively. Peroxide value and density values of
black chia seed oil were determined as 2.67meqO2/kg and 0.89 g/ml,
respectively (Alonso-Calderón et al., 2013). The highest saponifiable value were determined in cold pressed roasted (217.36 mg KOH/g) and non-roasted chia oils (220.54 mg KOH/g). Acid value, saponified value, unsaponifiable matter, and total wax of chia oils extracted by solvent extraction and pressing methods were determined as 2.05 and 0.91 mg KOH/g, 193.09 and 193.12 mg KOH/g, 1.27 and 0.85% and 142 and 108 mg/kg, respectively (Ixtaina et al., 2011). The results of Anjum, Anwar, Jamil and Iqbal (2006) and Javidipour, Erinç, Baştürk and Tekin (2016) support the results of physico-chemical parameters of microwave heated chia seed oils in the current study. Significant (p < 0.05) differences were however observed among other para-meters and results were partly differentiating from those reported in literature. It was observed that statistically significant differences among density values of oil heated in 360 and 540 W, saponification values of oil heated in 720 and 900 W, and unsaponifiable matter values of oil heated in 540 and 720 W. These differences can be attributed to variations in roasting processing, climatic factors, location and harvest time. The values of antioxidant activity for chia seeds sold in the market ranged from 1.474 to 2.602 mmol TEAC/g roasted for 2 and 40 min, respectively (Sargi et al., 2013). The content of total phenol of Chia seed extract was determined as 2.639 mg GAE/kg and 0.162 g equiva-lent/kg, respectively (Scapin, Schmidt, Prestes, & Rosa, 2016). Chia seed extracts contained 0.88 to 0.94 mg GAE/g total phenol ( Reyes-Caudillo, Tecante, & Valdivia-López, 2008; Coates & Ayerza, 2009). The IC50 value for chia seed extract was found to be 3.841 mg/ml and
45.004 mmol trolox equivalent/kg (Scapin et al., 2016).Sargi et al. (2013) reported that antioxidant capacity of Chia seed was 1.72%. Table 2present the correlations among physico-chemical properties of chia seed oil under different microwave heat treatments. Diverse cor-relations (positive, weak and negative) were observed among all parameters at different heating watts. Acidity and peroxide value have extreme significant possitive (***< 0.001, r2= 0.996) correlation
be-tween each other and they both showed exreme significant possitive (***p < 0.001, r2= 0.988 and 0.995, respectively) correlations with Table 1
Physico-chemical properties of chia oil heated in different microwave Watts.
Parameters Control 180 W 360 W 540 W 720 W 900 W
Acidity (mgKOH/g) 0.34 ± 0.07*f 3.81 ± 0.98e 6.77 ± 1.08d 13.54 ± 1.17c 18.66 ± 2.83b 23.58 ± 2.67a
Peroxide value (meqO2/kg) 1.17 ± 0.35f** 3.64 ± 0.72e 9.51 ± 1.56d 16.48 ± 3.26c 21.34 ± 1.83b 27.46 ± 1.54a
Density (g/ml) 0.9199 ± 0.0003e 0.9207 ± 0.0002d 0.9273 ± 0.0003c 0.9281 ± 0.0001c 0.9293 ± 0.0002b 0.9299 ± 0.0005a
Viscosity (mPa.s) 0.17 ± 0.03f 1.41 ± 0.17e 4.63 ± 0.13d 7.86 ± 0.21c 9.47 ± 0.21b 11.59 ± 0.13a
Saponification value (mgKOH/g) 218.87 ± 3.67a 218.03 ± 5.89a 217.86 ± 7.51b 216.54 ± 3.68c 215.49 ± 5.83d 215.03 ± 9.61d Unsaponifiable matter (%) 0.783 ± 0.008a 0.724 ± 0.003b 0.701 ± 0.007c 0.689 ± 0.009d 0.675 ± 0.018d 0.661 ± 0.011e
Total phenol (mgGAE/g) 0.91 ± 0.13a 0.83 ± 0.07b 0.74 ± 0.09c 0.71 ± 0.11d 0.67 ± 0.09e 0.55 ± 0.03f
Antioxidant activity (%) 0.72 ± 0.07a 0.65 ± 0.03b 0.59 ± 0.08c 0.55 ± 0.03d 0.51 ± 0.05e 0.38 ± 0.07f
Total wax (mg/kg) 112.74 ± 3.76a 103.64 ± 5.58b 93.81 ± 2.75c 91.17 ± 4.39d 81.58 ± 6.71e 57.17 ± 5.23f
* Each value is expressed as mean ± standard deviation.
viscosity. However, they showed extreme significant negative (***p < 0.001) correlations with saponifiable value (r2=−0.994 and
−0.983, respectively), total phenolic (r2
=−0.965 and −0.978, re-spectively), antioxidant activity (r2=−0.971 and −0.978, respec-tively), and total wax (r2=−0.954 and −0.960, respectively),
whereas they have negative (*p < 0.05) correlations with
unsaponifi-able matter (r2=−0.892 and −0.903, respectively). Density has po-sitive (*p < 0.05) correlations with peroxide value (r2= 0.824) and
viscosity (r2= 0.862), while it has negative (*p < 0.05) correlations
with unsaponifiable matter (r2
=−0.833) and total phenolics (r2=−0.833). Viscosity has negative correlations with saponifiable
value (***p < 0.001, r2=−0.977), unsaponifiable matter
(**p < 0.01, r2=−0.909), total phenolics (***p < 0.001, r2=−0.970), antioxidant activity (***p < 0.001, r2=−0.963), and
total wax (**p < 0.01, r2=−0.909). Saponifiable value has possitive
correlations with unsaponifiable matter(*p < 0.05,r2
= 0.891), total phenolics (**p < 0.01, r2= 0.943), antioxidant activity (**p < 0.01, r2= 0.949), and total wax (**p < 0.01, r2= 0.926). Unsaponifiable
matter has possitive correlations with total phenolics (**p < 0.01,
r2= 0.947), antioxidant activity (**p < 0.01, r2= 0.922), and total wax (**p < 0.01, r2= 0.881). Total phenolics and antioxidant activity
have extreme significant possitive correlations (***p < 0.001,
r2= 0.995) between each other and they both also have extreme sig-nificant possitive correlations with total wax (***p < 0.001, r2= 0.980
and 0.993, respectively).
Table 3shows fatty acid composition and tocopherol contents of oils extracted from chia seeds heated by microwave at different power. Generally, fatty acid compositions and tocopherol contents of the oil samples were partly reduced with the increase in microwave heating. The reduction in both fatty acids and tocopherol contents compared with the control group was observed in oil heated at 900 W power. Palmitic and stearic acid contents of chia oil samples changed between 7.09% (900 W) and 8.35% (control) to 1.81% (900 W) and 2.67%
(control), respectively. Also, while oleic acid contents of the oil samples heated in microwave oven range from 9.18% (900 W) to 10.08% (control), linoleic acid contents of oils changed between 19.21% (900 W) and 21.17% (control). Also, linolenic acid contents of chia seed oils heated in microwave varied between 66.84% (900 W) and 68.71% (control). Statistically significant differences were not observed among lauric, myristic, palmitic acid values of oil heated in 180–360 W and 720–900 W. Also, stearic contents of oil heated at 180, 360 and 540 W compared to control group were similar. Stearic acid contents of oil samples heated in microwave oven at different powers changed be-tween 1.81% (900 W) and 2.51% (180 W). When it was compared to control group, their values partly decreased. But, fatty acid composition of oils (except palmitic and stearic acids) heated at all microwave treatments were found statistically different compared to control group (p < 0.05).Sargi et al. (2013)reported that chia seed oil contained 5.8% palmitic, 2.4% stearic, 6.1% oleic, 17.4% linoleic and 54.4% li-nolenic (omega-3) acids. According toCoelho, Coelho, Schmidt, Prestes and Rosa (2014), chia seed contains 34.4% lipids out of which 62% are omega-3-fatty acid, 17.4% omega-6 and 10.5% omega-9-fatty acid.da Silva Marineli et al. (2014)reported thatα-linolenic acid of heated chia seed oil was the most prominent (62.80 g/100 g), followed by linoleic (18.23 g/100 g), palmitic (7.07 g/100 g), oleic (7.04 g/100 g) and stearic acid (3.36 g/100 g). Majority of lipids in chia seed were poly-unsaturated fatty acids, with linolenic being the most abundant 64.4%), followed by linoleic acid (19.5%) (Barreto et al., 2016). In addition, the results obtained for fatty acid composition in current study were found partly different to the findings of others (Ayerza, 2013; da Silva Marineli et al., 2014). Differences observed in fatty acid composition of chia oil may be attributed to the variation in climatic conditions, cul-tivation locations, agronomical practices, and genetic backgrounds of chia seeds, as well as esterification and analysis methods. The linolenic/ linoleic acid ratio of chia oil is higher than that reported for other ve-getable oils.Caponio et al. (2003)studied chemical properties of extra Table 2
Correlation coefficient among the physicochemical quality parameters of chia seed oil heated in different microwave watts.
Acidity Peroxide value Density Viscosity Saponification value Unsaponifiable matter Total phenolic Antioxidant activity Peroxide value 0.996*** Density 0.777 0.824* Viscosity 0.988*** 0.995*** 0.862* Saponification value −0.994*** −0.983*** −0.751 −0.977*** Unsaponifiable matter −0.892* −0.903* −0.833* −0.909** 0.891* Total phenolic −0.965*** −0.978*** −0.833* −0.970*** 0.943** 0.947** Antioxidant activity −0.971*** −0.978*** −0.778 −0.963*** 0.949** 0.922** 0.995*** Total wax −0.954*** −0.960*** −0.728 −0.934** 0.926** 0.881* 0.980*** 0.933***
Significant level:*p < 0.05;**p < 0.01;***p < 0.001.
Table 3
Fatty acid compositions and tocopherol contents of chia oil heated in different microwave Watts.
Fatty acids (%) Control 180 W 360 W 540 W 720 W 900 W
Lauric 0.06 ± 0.03*a 0.05 ± 0.02ab 0.05 ± 0.01b 0.04 ± 0.01c 0.03 ± 0.01d 0.03 ± 0.02d
Myristic 0.07 ± 0.01a** 0.05 ± 0.03ab 0.04 ± 0.01b 0.03 ± 0.01c 0.02 ± 0.01d 0.02 ± 0.01d
Palmitic 8.35 ± 0.56a 8.11 ± 0.84a 8.03 ± 0.71a 7.56 ± 0.34b 7.33 ± 0.28b 7.09 ± 0.63b
Palmitoleic 0.11 ± 0.03a 0.10 ± 0.05ab 0.08 ± 0.01c 0.07 ± 0.03d 0.05 ± 0.03e 0.03 ± 0.01f
Stearic 2.67 ± 0.53a 2.51 ± 0.32a 2.47 ± 0.21a 2.33 ± 0.17a 1.98 ± 0.43b 1.81 ± 0.35b
Oleic 10.08 ± 0.78a 9.77 ± 0.45b 9.51 ± 0.38c 9.43 ± 0.54d 9.37 ± 0.87e 9.18 ± 0.61f
Linoleic 21.17 ± 1.17a 20.11 ± 1.54b 19.97 ± 0.67c 19.78 ± 0.83d 19.46 ± 0.71e 19.21 ± 0.59f
Linolenic 68.71 ± 2.21a 68.09 ± 1.65ab 67.83 ± 2.64c 67.35 ± 2.98d 67.01 ± 1.51e 66.84 ± 3.42f
Arachidonic 0.19 ± 0.07a 0.17 ± 0.03ab 0.17 ± 0.05b 0.15 ± 0.03c 0.13 ± 0.01d 0.09 ± 0.03e
Tocopherols (mg/100 g) Control 180 W 360 W 540 W 720 W 900 W
α-tocopherol 51.17 ± 2.37a 50.24 ± 1.68b 49.81 ± 3.24c 49.64 ± 1.73c 48.07 ± 1.28d 47.71 ± 0.96e
β-tocopherol 67.81 ± 0.83a 66.75 ± 0.67b 66.05 ± 1.62b 65.78 ± 1.45c 64.32 ± 1.33d 62.58 ± 3.68e
ɣ-tocopherol 33.65 ± 1.35a 32.91 ± 3.84b 32.17 ± 2.71b 31.58 ± 1.98c 31.14 ± 0.74c 29.27 ± 3.28d
δ-tocopherol 2.17 ± 0.17a 1.97 ± 0.35b 1.65 ± 0.39c 1.60 ± 0.23c 1.47 ± 0.11d 0.98 ± 0.26e
* Each value is expressed as mean ± standard deviation.
virgin olive oil, groundnut oil and sunflower oil heated by conventional electric ovens and microwaves, and they have reported that both un-saturated and polyunun-saturated fractions are significantly reduced. This is related to the decrease of unsaturated fatty acids, and the increase in the percentage of the sum of saturated fatty acids (Barreto et al., 2016). Yoshida, Hirakawa, Tomiyama and Mizushina (2003) studied the ef-fects of microwave treatment on pumpkin seeds, and reported a change in the fatty acid composition of the pumpkin oil through the effect of microwave heating treatment. Also, changes in the fatty acid compo-sition after microwave pretreatment of oil seeds have been previously reported byTakagi and Yoshida (1999), Abbas, Hadi Bin Mesran, Abd Latip, Hidayu Othman, & Nik Mahmood (2016).Hassanein et al. (2003) has reported that polyunsaturated fatty acids were reduced as the mi-crowave heating time increases. Also,Majid et al. (2014)reported that the content of monounsaturated fatty acid varies slightly depending on the heat treatment and the ratio of polyunsaturated fatty acids de-creased. In addition,Abbas et al. (2016)have heated corn oil in mi-crowave for different watts and times and the the results obtained showed that the content of linoleic acid in the corn oil was reduced. In the current study,α-Tocopherol and β-tocopherol contents of the chia oil samples varied between 47.71 mg/100 g (900 W) and 51.17 mg/ 100 g (control) to 62.58 mg/100 g (900 W) and 67.81 mg/100 g (con-trol), respectively (Table 3). In addition,ɣ-tocopherol contents of oil samples changed between 29.27 mg/100 g (900 W) and 33.65 mg/ 100 g (control) whileδ-tocopherol contents of oils are determined be-tween 0.98 mg/100 g (900 W) and 2.17 mg/100 g (control). According to results, the key tocopherol of oil samples was β-tocopherol, and followed by α-tocopherol, β-tocopherol and δ-tocopherols. The de-crease in the content of tocopherol contents of samples during micro-wave heating could be due to the destruction of structure of the oil that are linked to tocopherol. Statistically significant differences were not exist amongβ-tocopherol and ɣ-tocopherol contents of oil heated at 180 and 360 W. But, all tocopherol contents of oil heated at all mi-crowave watts were found different statistically compared to control group (p < 0.05). Tocopherol content of chia seed oils ranged between 238 and 427 mg/kg, withγ-tocopherol and δ-tocopherol (> 85%) being the major ones, while varying levels (0.4–9.9 mg/kg) of α-tocopherol were also detected (Ixtaina et al., 2011). Tocopherols values obtained for chia oils in present study can be compared closely with the values reported for peanut oil (398.6 mg/kg), but lower than the values re-ported forflaxseed (588.5 mg/kg), sunflower (634.4 mg/kg) and soy-bean (1797.6 mg/kg) oils (Tuberoso, Kowalczyk, Sarritzu, & Cabras, 2007). Chia seed oil contained 190.66 and 202.40 µg/100 g α-toco-pherol, 94.45 and 81.91 µg/100 g β-tocopherol and 7472.97 and 7487.69 µg/100 g β-tocopherols (da Silva et al., 2017). Tocopherol composition of raw chia seed oil showed significant differences
(p < 0.05), and their tocopherol values were found higher than the heated seed oil. High levels of tocopherols in oil are related to the PUFA content (Tuberoso et al., 2007). It has been determined that tocopherols with different antioxidant activities decrease gradually with microwave heating (Yoshida, Tatsumi, & Kajimoto, 1992). It has been observed that after heating a mixture of sunflower, soybean, peanut and a mix-ture of soybean and peanut oils in the microwave at 227 °C for 18 min, the content of tocopherol and the duration of exposure are inversely proportionalHassanein et al. (2003). These results show partial simi-larity to those obtained byAlbi et al. (1997b)that reported 72 and 85% of tocopherols losses after microwave heating (120 min, half-power) of sunflower oil and high oleic sunflower oil, respectively. The microwave heating time also affects the fatty acid compositions and tocopherol contents which clearly decreased as long as the exposure time increases. After 15 min of heating the electro-chemical signal, due to the toco-pherol, disappear completely in the voltamogram (Malheiro et al., 2009). Tocopherols are usually completely destroyed before the point at which the frying oil should be replaced based on the content of polymerised triacylglycerols or polar compounds (Reblova, Tichovska, & Doležal, 2009). In addition, the microwave heating time did not promote the occurrence of hydrolysis in the samples since no changes in fatty acid composition were found.
Phenolic compounds of chia seed oils obtained by cold pressing and heated by microwave oven are shown inTable 4. The major phenolic compounds are caffeic, rosmarinic, genistein and myrcetin. Microwave heating had greatly affected the quantitaties of phenolic compounds. In particular, the amounts of phenolic constituents of oils heated at 720 and 900 W were reduced at significant levels. While caffeic acid con-tents of the oil samples change between 0.27 mg/g (900 W) and 3.84 mg/g (control), rosmarinic acid contents of samples varied be-tween 1.32 mg/g (900 W) and 3.17 mg/g (control). In addition, genis-tein contents of chia oils changed between 0.08 mg/g (900 W) and 1.32 mg/g (control) while myrcetin contents of the oil samples vary between 0.53 mg/g (900 W) and 1.24 mg/g (control). A decrease in phenolic components were observed with increasing microwave heating power. This reduction was detected in the oil samples heated up to 900 W. At the same time, the amounts of the phenolic components at the beginning of the microwave heating were very close to the control group. Also, the quantitites of the other phenolic components of oil samples were < 0.50 mg/g, and their amounts decreased with in-creasing microwave heat. Phenolic constituents of chia seeds showed differences depending on roasting conditions.Coelho et al. (2014) re-ported that chia seed extract contain 4.68 µg/g cinnamic acid, 30.89 µg/g caffeic acid, 0.17 µg/g quercetin. Chia seed extracts con-tained 0.0307–0.102 mg/ml chlorogenic acid, 0.005–0.0068 mg/ml caffeic acids, 0.125–0.268 mg/ml quercetin, 0.301–0.509 mg/ml Table 4
Phenolic compounds of chia oil heated in different microwave powers (mg/g).
Penolics Control 180 W 360 W 540 W 720 W 900 W
Gallic 0.13 ± 0.05*a 0.12 ± 0.03ab 0.10 ± 0.03c 0.09 ± 0.01c 0.07 ± 0.03d 0.03 ± 0.01e
(+)-catechin 0.25 ± 0.07a 0.23 ± 0.09b 0.21 ± 0.03c 0.17 ± 0.05d 0.15 ± 0.01e 0.07 ± 0.03f
Syringic 0.21 ± 0.03a 0.20 ± 0.05ab 0.18 ± 0.01c 0.16 ± 0.03d 0.13 ± 0.07e 0.08 ± 0.03f
Cinnamic 0.17 ± 0.05a 0.15 ± 0.03b 0.12 ± 0.01c 0.11 ± 0.03c 0.07 ± 0.01d 0.03 ± 0.01e
Vanillic 0.14 ± 0.01a 0.11 ± 0.05b 0.09 ± 0.03c 0.08 ± 0.01c 0.06 ± 0.01d 0.02 ± 0.01e
Caftaric 0.47 ± 0.11a 0.45 ± 0.09ab 0.39 ± 0.07c 0.37 ± 0.03c 0.31 ± 0.05d 0.18 ± 0.05e
Caffeic 3.84 ± 0.19a 3.23 ± 0.21ab 0.65 ± 0.38c 0.59 ± 0.11d 0.42 ± 0.09e 0.27 ± 0.03f
Coumaric 0.43 ± 0.09a 0.42 ± 0.11ab 0.38 ± 0.13c 0.36 ± 0.09d 0.29 ± 0.03e 0.14 ± 0.07f
Ferulic 0.19 ± 0.01a 0.17 ± 0.03b 0.15 ± 0.03c 0.14 ± 0.05c 0.11 ± 0.02d 0.05 ± 0.01e
Quercetin 0.18 ± 0.03a 0.15 ± 0.07b 0.14 ± 0.01c 0.14 ± 0.03c 0.09 ± 0.03d 0.04 ± 0.01e
Kaempherol 0.24 ± 0.01a 0.21 ± 0.05b 0.19 ± 0.03c 0.19 ± 0.07c 0.17 ± 0.05d 0.09 ± 0.03e
Rutin 0.19 ± 0.05a 0.16 ± 0.03b 0.14 ± 0.01c 0.13 ± 0.03c 0.09 ± 0.03d 0.02 ± 0.01e
Genistein 1.32 ± 0.11a 1.29 ± 0.17b 1.25 ± 0.09c 0.21 ± 0.07d 0.17 ± 0.03e 0.08 ± 0.03f
Rosmarinic 3.17 ± 0.09a 3.11 ± 1.15ab 3.07 ± 0.21c 2.87 ± 0.27d 2.53 ± 0.32e 1.32 ± 0.28f
Myrcetin 1.24 ± 0.13a 1.21 ± 0.09ab 1.18 ± 0.14c 1.15 ± 0.21c 1.04 ± 0.09d 0.53 ± 0.07e
Isorhamnetin 0.44 ± 0.05a 0.42 ± 0.09ab 0.40 ± 0.11c 0.37 ± 0.07c 0.31 ± 0.03d 0.17 ± 0.05e
kaempherol and 0.379–0.881 mg/ml total phenols as reported else-where (Reyes-Caudillo et al., 2008). The results obtained in current study differ from those reported in literature.Ayerza (2013)reported that Tzotzol and Iztac Chia genotypes contained 0.115 and 0.121 mg/g myrcetin, 0.007 and 0.006 mg/g quercetin, 0.025 and 0.024 mg/g kaempherol, 0.226 and 0.218 mg/g chlorogenic acid and 0.139 and 0.149 mg/g caffeic acids, respectively. The result showed that phenolic compounds were significantly (p < 0.05) higher in chia seed oil de-pending on roasting conditions. Generally, significant differences were not found in the phenolic compounds namely gallic, cinnamic, vanillic, caftaric, ferulic, quercetin, kaempherol, rutin, myrcetin and iso-rhamnetin contents of chia seed oils heated at 360 and 540 W. How-ever, other phenolic constituents of oils heated at all microwave powers were found statistically different compared with control group (p < 0.05).Albi et al. (1997a)reported that total polyphenol contents of extra virgin olive oil and olive oil heated by conventional methods were reduced at the rate of 64% and 10%, respectively. In another study, when virgin olive oil and olive oil were subjected to microwave heating for 120 min, losses of 96 and 85% in the total polyphenols content, respectively were reportedAlbi et al. (1997b).
4. Conclusion
The results showed that microwave heating led to considerable losses in the quality attributes of chia oil extracted from the seeds he-ated at different microwave watts. Microwave roasting of chia seeds had significant (p < 0.05) effects on physico-chemical and bioactive properties of chia oils heated at different microwave powder. Generally, fatty acid compositions and tocopherol contents of the oil samples partialy decreased together with microwave power’s increase. The heat reduction in both fatty acids and tocopherol contents was observed in oil heated at 900 W compared with the control group. Lauric, myristic, palmitic acid values of oil heated in 180 to 369 W and 720 to 900 W and stearic of chia oil extracted from the seeds roased at 180, 360, and 540 W were not significantly different. All tocopherols of chia oil ex-tracted from the microwave roasted seeds were statistically different compared to control group (p < 0.05). The major phenolic compounds in chia seed oil are caffeic, rosmarinic, genistein and myrcetin. A de-crease in phenolic components were observed with increasing micro-wave heating power. Overall, much care should be taken when roasting chia seeds in microwave to avoid lossess in the bioactive components of chia seed oil.
Acknowledgment
The authors extend their appreciation to the Deanship of Scientific Research, King Saud University, Riyadh, Kingdom of Saudi Arabia, Grant Number (RG-1439-80).
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