Lipid components and oxidative status of selected specialty oils

Muchos aceites vegetales se venden como aceites especiales debido a su flavor, gusto y características distintas. Muestras de aceites especiales de almendra, avellana, nuez, nuez de macadamia, argán, aguacate, semillas de uva, de sésamo tostadas, salvado de arroz, y aceites orgánico de semillas de colza prensado en frío y, prensado caliente, y refinados que se producen y comercializan al por menor, se obtuvieron en comercios de grandes superficies en Reading, Reino Unido, y Uppsala, Suecia, y se les determinó su composición detallada de lípidos y su estado oxidativo. Los niveles de peróxidos (PV) fueron bastante bajos (0,5 a 1,3 mEq O2/kg), pero la acidez (AV) y los valores de la estabilidad oxidativa Rancimat a 100 °C (excepto los aceites de colza) variaron considerablemente (0,5-15,5%) y (4,2 a 37,0 h), respectivamente. El aceite de nuez de macadamia se encontró que fue el aceite más estable, seguido por el aceite de argán, mientras que el aceite de nuez fue el menos estable. Entre los aceites especiales, el aceite de nuez de macadamia, presentó el menor nivel de ácidos grasos poliinsaturados (AGPI) (4%) y aceite de nuez el más alto (71%). El aceite ecológico de colza prensado en frío tenía un contenido considerablemente menor de AGPI (27%) en comparación con otros aceites de colza (28-35%). En todas las muestras, α-y γfueron los principales tocoferoles, y el aceite de nuez presentó los niveles más bajos. Los esteroles totales variaron desde 889 hasta 15.106 mg/g de aceite. Los principales esteroles fueron: β-sitosterol (61-85%) y el campesterol (6-20%). El aceite de argán contenía schottenol (35%) y espinasterol (32%). En comparación con los valores de la literatura, no se observaron diferencias significativas entre los aceites de colza procesados de manera diferente, cultivado ecológicamente y prensado en frío y otros aceites especiales de este estudio.


INTRODUCTION
Among edible fats and oils, a considerable number of products are sold as specialty oils which have undergone minimum or no processing.Examples of such products, commonly known as specialty oils, include extra virgin olive oils, oils extracted from different nuts, cold pressed rapeseed oils, etc.Many specialty oils are unique in flavor, odor and special characteristics which suggest their specific use for cosmetic, therapeutic and dietary purposes.Rapeseed oil represents the most common vegetable oil consumed in Sweden along with other Nordic countries.Among the different commercially available rapeseed oils, cold pressed oils generally claim higher quality.They are extracted without applying heat and promoted as specialty oils, sold at a higher price.The cold S.R.P. MADAwALA, S.P. KOCHHAR AND P.C. DUTTA pressed oil products may contain both pro-and antioxidative compounds and that would affect the quality of these oils (Pekkarinen et al., 1998).
The general perception of consumers is that foods grown organically and subjected to less processing are better and healthier and thus cold pressed oil is an appealing choice since no solvents and no further processing other than filtering are involved (Koski et al., 2002).Studies reveal that organic crops tend to contain higher dry matter, certain minerals, antioxidants (phenols, resveratrol) and lower amounts of nitrates, residues of toxic chemical pesticides, fungicides and herbicides compared with conventionally grown crops (Lairon, 2010).In order to comply with these trends and environmental concerns, the edible fats and oils industries are also developing milder processing conditions (Jung et al., 2009).
Extensive studies have shown that plant sterols and stanols reduce total-and LDL-cholesterol levels in humans (Normen et al., 2004).Through a study with home prepared foods in real-life conditions, it has been found that part of the beneficial effects of the enhanced Mediterranean diet on the lipid profile is due to an increased consumption of phytosterols and other constituents which might be bioactive even in small amounts in their natural food matrix (Escurriol et al., 2009).Natural oils are also preferred due to higher levels of other bioactive components such as squalene, tocopherols and tocotrienols compared with their processed counterparts.Beyond the active role of α-tocopherol, it has been found that γ-and d-tocopherols and tocotrienols have a specific pharmaco dynamic profile due to their different metabolic patterns (Franke et al., 2007).For studying the overall quality of oil, the parameters such as detailed fatty acid composition, content and composition of unsaponifiables (sterols, tocopherols, etc.) and oxidative status and stability are generally assessed.The stability of oil is important for nutritional and functional quality as well as for its organoleptic properties.
Studies on the effects of minor oil components on oxidative status for differently processed rapeseed oils are scarce (Pekkarinen et al., 1998, Koski et al., 2002).To our knowledge, no published data on minor lipid components is available for commercially available, organically grown, cold pressed rapeseed oil.The main objective of this study was to evaluate the oxidative status and stability of selected specialty oils commercially available in the UK, commercial samples of differently processed rapeseed oils, and organic and cold pressed rapeseed oils collected in Sweden in relation to their fatty acid profiles and minor antioxidant components.

Determination of peroxide value (PV)
Approximately 0.02g of lipid sample in triplicate were used to analyze PV following the IDF standard method 7A (1991).

Determination of p-anisidine value (AV)
AV was determined using 2.5 g oil in triplicate according to the published method of the IUPAC (1987).

Determination of oxidation stability by Rancimat
The Oxidation stability of the oils was measured using 2.5 g oil sample in duplicate as described previously by Savage et al. (1997), except that accelerated oxidation was performed at 100 °C and 20L/h air flow rate using a Rancimat 679 (Metrohm, Herisau, Switzerland).

Analysis of fatty acid methyl esters (FAME)
Preparation of FAME was done using 10 mg oil samples and analyzed by capillary column GC according to the published method (Azadmard-Damirchi and Dutta, 2008).

Analysis of tocopherols and tocotrienols
Tocopherols and tocotrienols were analyed by direct injection of the oil samples dissolved in HPLC grade heptane (ca.10mg/ml) using an HPLC coupled to a fluorescence detector according to the method published previously (Azadmard-Damirchiand Dutta, 2008).
LIPID COMPONENTS AND OxIDATIVE STATUS OF SELECTED SPECIALTy OILS

Analysis of sterols by GC and GC-MS
The Trimethylsilylether derivatives of sterols after saponification of the oil samples (ca.20 mg) were determined by capillary column GC using 5α-cholestane as internal standard according to the published method (Azadmard-Damirchi and Dutta, 2008).Confirmation of the sterol structures was made with GC-MS using a GC 8000 Top Series GC and an AS800 auto sampler (CE Instruments, Thermo Quest Italia S.P.A., MI, Italy) coupled to a Voyager mass spectrometer with xcalibur version 1.2 (Finnigan, Thermo Quest, Manchester, UK).The column and conditions used were the same as for the GC.

Fatty acid composition
The fatty acid profile of the different specialty oils is presented in Table 1.The high polyunsaturated fatty acid (PUFA) contents (71 and 69% respectively) observed in walnut and grape seed oil explained the low oxidative stability of these oils.Oleic acid (18:1) was the predominant fatty acid in all the oils except for the walnut and grape seed oils in which linoleic acid (18:2) was observed at higher levels.walnut oil had a significantly high amount of linolenic acid (18:3) which was 10.4% compared with 0.3% in grape seed oil.Macadamia nut, hazelnut, avocado, almond and rapeseed oils showed the highest levels of monounsaturated fatty acids (MUFA).Macadamia nut oil contained 18% palmitoleic acid (16:1) which was not common in many specialty oils.According to the published literature (Charrouf and Guillaume, 2008;Crews et al., 2005Crews et al., , 2005Crews et al., , 2006;;Dubois et al., 2007;Kochhar, 2002;Lu et al., 2009;Maguire et al., 2004;Rubio et al., 2009;Savage et al., 1997Savage et al., , 1999)), in all the oils tested, SFA (saturated fatty acid) levels were comparatively low except for rice bran and argan oil.Among differently processed rapeseed oils, the level of SFA was very similar 6-7%.MUFA varied from 59-66% with oleic acid being the dominant one.The PUFA contents in these samples varied from 28-35% and linoleic acid was observed as the dominant fatty acid (18-22%), and the linolenic acid content varied from 8-12%.Organic cold pressed rapeseed oil had a bit higher level at 18:1 (62%) compared with the other rapeseed oils (54-61%).This higher level of oleic acid was compensated by the lower levels of 18:2 (18%) and 18:3 (8%).The ranges of these fatty acids in the other rapeseed oil samples were (18 -22%) and (8-12%), respectively.All the rapeseed oil samples had relatively higher levels of vaccenic acid (3-4%) compared with other specialty oils, as shown in Table 1.The fatty acid profiles observed for different brands of rapeseed oils were generally uniform and concur with the published data (Dubois et al., 2007;Koski et al., 2002).No data is known to our knowledge on fatty acids in organic rapeseed oil, however, a previous study has shown that the level of oleic acid was higher in organic virgin olive oil (Gutiérrez et al., 1999).we did not make any effort to identify trans fatty acids in the samples.If there were any trans fatty acids present in some samples those are presented under the column "Others" in Table 1.It has been reported that minor amounts of trans fatty acids are present in commercially refined edible oils.The authors have cautioned that deodorization temperature is critical to minimize the formation of trans fatty acids in oils containing high amounts of polyunsaturated fatty acids (Tasan et al., 2011).

Tocopherol (Tp) and tocotrienol (Tt 3 ) content
The contents of different isomers of tocopherol (Tp) and tocotrienol (Tt 3 ) in the different specialty oil samples showed wide variations (Table 2).α-Tp and γ-Tp were the main isomers present in all the specialty oil samples.In almond, hazelnut, avocado and grape seed oils, the predominant isomer was α-Tp, while γ-Tp was predominant in all the other samples.Among the different tree nut oils, macadamia nut oil showed the lowest Tp and Tt 3 and the total tocopherol level was only 54 µg/g oil.This was comparable with the data published by Kaijser et al. (2000).
In accordance with the data published by Crews et al. (2006), only γ-Tp could be detected in roasted sesame oil.According to Kochhar (2002), the Tp in crude sesame oils can vary from 400-700 µg/g of which γ-Tp is predominant along with a small proportion of d-Tp.The roasting of sesame seeds improves the oxidation stability of its oil and thereby protects antioxidant compounds like tocopherols in the oil.
The highest Tt 3 levels were observed in rice bran and grape seed oil.The different levels of different Tp observed in argan oil were well in accordance with the data published previously by Khallouki et al. (2003).The relatively high stability of rice bran oil is most likely due to the combined effect of oryzanol, phytosterols, squalene, tocopherols and tocotrienols, while the stability of roasted sesame oil is due to the higher antioxidant activity of the sesamol formed from sesamolin during roasting and the high level of potent γ-tocopherol antioxidants (Kochhar, 2002).
Among the specialty samples investigated, hazelnut oil and macadamia nut oil contained α-Tt 3 , whereas ricebran oil and roasted sesame oils contained high amounts of both α-Tt 3 and γ-Tt 3 (Table 2).The literature values concerning total tocopherols in sesame oils vary widely ranging from 88-1609 µg/g oil (Kochhar, 2002).The total tocol content in ricebran oil in our study (567 µg/g) is in good agreement with this data and Abidi (2003).In walnut oil, γ-and d-Tp contents were in accordance with the data published by Crews et al. (2005) except for α-Tp.The predominant isomer γ-Tp represents 69% of the total tocol contents (373 µg/g) which is a similar finding to published data (Crews et al., 2005;Miraliakbari and Shahidi, 2008).The level of γ-Tp in the rapeseed oil samples was generally higher (396 -474 µg/g oil) compared with other oils except for argan and sesame oil samples which contained 463 and 521 µg/g oil, respectively.The highest level of α-Tp was observed in fully refined and warm pressed rapeseed oil samples followed by the organic cold pressed rapeseed oil sample.The high total Tp observed in the warm pressed sample may suggest better extraction of the tocopherols from the structural components of seeds (Falk and Munné-Bosch, 2010).Alpha and γ-Tp in rapeseed oil samples were comparable with the published data (Koski et al., 2002, Schwartz et al., 2008).In the latter study, it was shown that organic rapeseed oil had a generally lower content of α-Tp but slightly higher level of γ-Tp, compared with refined and cold pressed rapeseed oils.

Sterol content
The content and composition of sterols in different specialty oil samples are presented in Table 3.The total sterol content of the oil samples varied in a range between 889-6204 µg/g oil, except for the rice bran oil.The predominant sterol was β-sitosterol followed by other common desmethyl sterols such as campe-, stigma-and D5-avenasterol in all the samples except in argan oil.Individual as well as total sterol contents in hazelnut oil were in good agreement with the published data (Crews et al., 2005).A rather similar sterol profile was found in the avocado oil sample but the total sterol content was twice the amount observed in nut oils.
Argan oil showed a characteristically different sterol profile compared to all the other oil samples.The major sterols identified were schottenol which represents 51% and spinasterol with 46% of the total identified sterols.The observed sterol profile of argan oil was comparable with the data published by Khallouki et al. (2003).However, the content of each type of sterol observed in our study was much lower than their values.The total sterol content of grape seed oil was in agreement with the Codex range (1999) and for Italian varieties (Crews et al., 2006).Though the origin of the grape seed oil in our study is not known, the relative proportion of the individual sterols identified as% total identified were similar to the Italian varieties rather than the French and Spanish varieties analyzed in their study.The individual and total sterol contents observed in our study for roasted sesame oil were in the range mentioned by Crews et al. (2006).Rice bran oil contained the highest amount of sterols in this study, which concurs with the published literature (Kochhar, 2002, Piironen et al., 2000).In addition to the highest total sterol levels, a considerably high level of stigmasterol (13%) was observed in the rice bran oil sample compared with the other oil samples analyzed.
The content of sitosterol greatly varied from 1489-3340 µg/g in the rapeseed oil samples.Sitosterol was the predominant sterol (44-49%) but as an individual sterol, sitosterol was lower when compared with the other specialty oil or nut oil samples analyzed in this study (Table 3).The lower proportion of sitosterol was compensated by a higher percentage of campesterol.The brassicasterol content varied from 282-874 µg/g while it was 1145-2655 µg/g for campesterol, and D5-avenasterol was present in moderate levels.Despite the variation in individual sterol contents among the different rapeseed oil samples, their relative proportions remained uniform.The content of different sterols observed were in line with previously published data (Schauss, 2008;Schwartz et al., 2008).The authors observed no clear relationship regarding their origin such as organic rapeseed oil or the processing method.However, the relative proportion of brassicasterol in organic rapeseed oil sample (7%) was considerably lower compared to other rapeseed oil samples.The authors also confirmed that sterol contents were roughly the same in crude and refined rapeseed oil or cold pressed organic rapeseed oils.
Variations in individual and total sterol contents in the oil can be due to genetic factors among varieties, growing and storage conditions, refining, etc., but the relative percentage composition of individual sterols generally remains similar.Some plant sterols are partly removed during industrial oil refining depending on the extent of refining conditions (Piironen et al., 2000).In our study, the lowest level of D5-avenasterol (101 µg/ g oil) was observed in the warm pressed rapeseed oil sample compared with the other rapeseed oil samples and ranged from 145-382µg/ g oil.In addition, the lowest total sterol content was observed in the warm pressed rape seed oil sample, with the exception of one sample (cold pressed 2 rapeseed oil).

Table 3 Content (µg sterols/g oil) and composition (%) 1 of different sterols in different specialty oils
LIPID COMPONENTS AND OxIDATIVE STATUS OF SELECTED SPECIALTy OILS