This work aimed to determine the major and minor compounds of avocado oils. Mono-varietal oils from the Bacon, Fuerte, Hass, and Pinkerton cultivars were obtained by means of an Abencor® system, while commercial oils from Brazil, Chile, Ecuador and New Zealand were purchased locally. The content of triacylglycerols, fatty acids, aliphatic and terpenic alcohols, desmethyl- methyl- and dimethyl-sterols, squalene and tocopherols were determined. The main triacylglycerols were those with ECN48. In addition, the oleic, palmitic and linoleic acids prevailed. Desmethyl-sterols were the principal minor compounds. Low amounts of aliphatic and terpenic alcohols were also found. Squalene concentrations were higher in Bacon, Fuerte and Pinkerton oils than in the other oils. The most abundant tocopherol was α-tocopherol. Partial least squares discriminant analysis made it possible to express the differences among the samples. To summarize, this work brings a different approach to the complete characterization of avocado oil.
Avocado oil is extracted from the pulp of
According to FAO, Mexico is the world’s largest producer of avocados. In 2014, this country produced 1.52 million tons of avocado fruits, around 30% of the world stock (FAOSTAT,
Taxonomically, the
Although several methods have been proposed for obtaining avocado oil, including enzyme, solvent and supercritical fluid extraction (Freitas
The fatty acid composition of avocado oil has been reported in several studies, describing oleic acid (C18:1ω9) as the main one. This fact has been used as support for studies that aim to prove the beneficial health effects of this oil, such as a reduction in effects from diabetes, oxidative stress on the mitochondrial membrane and cardiovascular disease markers (Ortiz-Avila
In order to achieve the standardization of avocado oil, Woolf
Therefore, the aim of this work was to characterize mono-varietal avocado oils from the Bacon, Fuerte, Hass and Pinkerton cultivars as well as commercial avocado oils from Brazil, Chile, Ecuador and New Zealand. This approach greatly contributes to the knowledge about the chemical composition of such oil, supporting the establishment of legislative standards.
Acetone, diethyl ether, hexane, propionitrile, and tetrahydrofuran (THF) were supplied by VWR International (West Chester, PA). Potassium hydroxide was from Panreac (Montcada I Reixac, Barcelona, Spain). Silica-solid phase extraction (Si-SPE) cartridges were from Varian (EA Middelburg, The Netherlands). Standards of fatty acid methyl esters (FAME, Supelco 37 component mix), 5-α-cholestan-3β-ol, squalane and n-eicosanol were from Sigma-Adrich Co. (St. Louis, MO). Hexamethyl disilazane, pyridine, trimethyl chloroxilane and standards of tocopherols were from Merck (Merck Group, Darmstadt, Germany). All chemical reagents were at least analytical grade.
Mature fruit samples of the Bacon, Fuerte, Hass and Pinkerton cultivars were provided by Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora (IHSM-CSIC, Málaga-Spain). The avocado fruits arrived at the laboratory the day after the harvest under perfect phytosanitary conditions. The oil content was extracted two days after the fruits arrived at the laboratory at the Instituto de la Grasa (Sevilla-ES), by means of an Abencor® system, described in Section 2.4. Throughout the storage time, the fruits were kept at room temperature and no changes were noted. Commercial avocado oil samples from the Hass variety were obtained from common and commercial brands in a local grocery store from Brazil, Chile (named ‘Chile A’ and ‘Chile B’), Ecuador, and New Zealand. Four bottles with 500 mL of each sample were purchased from the same lot. They were taken to the laboratory, at the Instituto de la Grasa (Sevilla-ES), by air mail, and properly stored at 4 °C until analysis. For ethical reasons no commercial brand will be cited in this paper.
For each extraction, 500 g mature avocados, without seeds, were milled in a knife mill and the paste was taken for extraction by means of an Abencor® system malaxer, and centrifuge (MC2 Ingenierıa Sistemas, Seville, Spain) followed by an additional centrifugation step. Malaxation was carried out below 40 °C for 40 min, with talc addition (~10g·100g–1 paste). Distilled water, (20 mL·100g–1 paste) was added after 10 min of starting the malaxation process. The first centrifugation was carried out in the Abencor® system centrifuge at 3000 rpm during 60 s. The paste was then spilt out and the liquid phase was further centrifuged in a bench centrifuge (5000 rpm, 10 min). The oil obtained was filtered and stored at 4 °C until analysis.
A multivariate statistical analysis was performed with the complete information from the chemical characterization. The tables of data were saved as .csv files and uploaded onto the Metaboanalyst 3.0 web-based tool (Xia
In order to select the most important features for sample grouping, we used the variable importance in projection (VIP-score) calculation for the component 1. We plotted the VIP score for the ten most important features to distinguish the sample.
It is important to clarify that we used the PLS-DA as a multivariate statistic tool to represent the relationships among the full chemical compositions of the samples. We did not use this tool to create a mathematical model to classify samples, since we believe that more studies must be done on different crops, growing places, ripening stages and shelf life to create a valid model.
The FA profile is the most common parameter for oil characterization. It is widely described in many books and in the legislation.
Fatty acid compositions of avocado oil samples. Average (bold) ± standard deviation of three replicates
Monovarietal Avocado Oil |
Commercial Avocado Oil |
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Sample | Bacon | Fuerte | Hass | Pinkerton | Brazil | Chile A | Chile B | Equator | New Zealand |
Fatty Acid Profile % area | |||||||||
ND – Non-detected Value
All results obtained in the FA composition are within the ranges already described for avocado oil and cited in the Introduction. Nonetheless, looking at the quality standards proposed by Woolf
Another important observation is that the fatty acid profiles obtained for these avocado oil samples were quite similar to those described for other vegetable oils, such as olive oils and nut oils (IOC,
The FA distribution in the TAG is another important identity parameter related to the saponifiable fraction of lipids. The experimental TAG profiles are described in
Triacylglycerol compositions of avocado oil samples. Average (bold) ± standard deviation of three replicates
|
Sample |
Monovarietal Avocado Oil |
Commercial Avocado Oil |
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Bacon | Fuerte | Hass | Pinkerton | Brazil | Chile A | Chile B | Equator | New Zealand | ||
TAG Profile % area | ||||||||||
P – Palmitic acid; Po – Palmitoleic acid; S – Stearic acid; O – Oleic acid; L – Linoleic acid; Ln – Linolenic acid
ND – Non-detected Value
Minor compounds are widely related to fat and oil identity and they are normally found in the unsaponifiable matter (Gómez-Coca
Sterol fractions from the minor compounds of avocado oil samples: desmethyl-, methyl- and dimethyl-sterols. Average (bold) ± standard deviation of three replicates
Monovarietal Avocado Oil |
Commercial Avocado Oil |
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Sample | Bacon | Fuerte | Hass | Pinkerton | Brazil | Chile A | Chile B | Equator | New Zealand |
Desmethylsterols % area | |||||||||
ND – Non-detected Value
Minor compounds in avocado oil samples: squalene, terpenic alkenols, aliphatic alcohols, and tocopherols. Average (bold) ± standard deviation of three repilcates
Monovarietal Avocado Oil |
Commercial Avocado Oil |
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Sample | Bacon | Fuerte | Hass | Pinkerton | Brazil | Chile A | Chile B | Equator | New Zealand |
Squalene mg·kg–1 | |||||||||
ND – Non-detected Value
Regarding methyl-sterols, Pinkerton was the sample with the highest concentration (1091.66±2.84 mg·kg–1); whereas Chile A had the lowest one (287.98 ±7.32 mg·kg–1) among all the analyzed oils. Within this class, citrostadienol was the predominant compound ranging from 71.21±0.21% (Ecuador) to 83.04±0.23% (Bacon). Dimethyl-sterols, the most variable class of compounds within the sterol group, were present at values from 39.68±1.56 mg·kg–1 in Chile B to 545.33±25.84 mg·kg–1 in Pinkerton. Bacon was the only sample in which 24-methylen cycloartenol was relevant (74.47±0.58%) since in the other cases, cycloartenol was always the main compound oscillating between 50.77±0.62% in Pinkerton and 70.43±3.24% in Chile B.
The health effects of squalene have already been described and they come mainly from olive oil consumption (Newmark,
Phytol and geranylgeraniol are primary alkenols with terpenic skeletons. Total concentrations were below 100 mg·kg–1 for all samples. Chile B oil was the sample with the highest amount, 92.36±16.46 mg·kg–1, and the New Zealand oil sample contained the lowest, at 41.68±2.04 mg·kg–1. Geranylgeraniol was normally the compound in the highest proportion among all of them (54.97±3.14%-79.44±2.47%), except for the case of Chile A oil, in which the proportion of the two compounds were almost the same.
The aliphatic alcohol profile is dominated by molecules with even carbon numbers, such as C22-OH, C24-OH, C26-OH, and C28-OH. In the Bacon, Brazil, Fuerte, Hass, New Zealand and Pinkerton cultivars the main alcohol was C22-OH (31.59±0.09%-43.75±6.35%;, whereas in Chile A and B samples, C26-OH was the main one (21.34±4.18% and 31.59 ±1.36%, respectively). Only in the Ecuador sample, C28-OH stood out among the others (27.28 ±6.79%).
The presence and the concentration of tocopherols are closely related to both identity and quality since these molecules have antioxidant activity and may indicate the resistance of oil to oxidation as well as the fact of having been exposed to oxidation conditions. The total amount of tocopherols (
Generally, α-tocopherol was the main species found, except in Bacon, where γ-tocopherol was the most abundant one. Tocotrienols were not found in these samples.
To the best of our knowledge, these approaches to avocado oil characterization (detailed characterization of major and minor compounds from the same sample) have never been published, which makes both the election of relevant characterization parameters and the subsequent discussions difficult. In this line, we performed a PLS-DA test in order to find relationships among samples and to determine which parameters were more important to establish these relationships.
After the statistical analysis described in the Material and Methods section, the distribution graphic based on components 1 and 2 was chosen, and explained more than 35% of the data variance. As
Partial least square discriminant analysis plot for all analyzed samples with 95% confidence region, C1 × C2
The VIP scores in
Scores of variable importance in the projection of Component 1
It is essential to note that
Avocado oil can be considered mainly a monounsaturated oil, with oleic acid as the main FA. The TAG composition is also dominated by oleic acid. The presence of ω7, ω9 and ω11 isomers of oleic and palmitoleic acids in avocado oil were described for the first time.
Desmethyl-sterols were determined, with β-sitosterol as the main molecule we found. The squalene concentrations were higher in Bacon, Fuerte and Pinkerton oils, than in Hass and commercial oils; those oils may be suggested as potential squalene sources. Tocopherols (but not tocotrienols) were also found, and were mainly α- and γ-tocopherol.
Minor compounds like methyl- and dimethyl-sterols, terpenic alkenols, and aliphatic alcohols were described for the first time in this work.
From the global data, it was also possible to distinguish which features were more important for sample differentiation. PLS-DA and its VIP scores revealed statistical differences among the samples, mainly related to commercial oils. Such differences should be taken into account for establishing future regulatory laws.
We thank the Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora (IHSM-CSIC, Málaga-Spain) for providing the avocado samples, the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil) and the National Council for Scientific and Technological Development (CNPq, Brazil) for the scholarship and financial assistance.