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Introduction
Bacuri, Attalea phalerata Mart. ex Spreng. is a palm that belongs to the Arecaceae family, and is also known as acuri or guacuri (Negrelle, 2015). It is widely distributed in the Brazilian states of Mato Grosso do Sul and Mato Grosso. The pulp has colors that range from yellow to orange due to the presence of carotenoids, and some of these are vitamin A precursors (Coimbra & Jorge, 2013). Its fruits are used cooked to prepare juices, jellies, and ice cream due to its high nutritional value and sensory attributes (Negrelle, 2015). The pulp oil is also rich in saturated fatty acids, as well as polyunsaturated and monounsaturated acids. It is also used by the local population to relieve joint pain and as a hair tonic (Lima et al., 2017).
Vegetable oils rich in health-beneficial compounds are in great demand due to consumer interest in disease prevention and health promotion. These compounds include phenolics, carotenoids, tocopherols, antioxidants, and fatty acids with a high content of mono and polyunsaturated acids (Parry et al., 2005).
It is exceedingly beneficial to consume monounsaturated and polyunsaturated fatty acids through the diet. The omega-3 polyunsaturated fatty acids are precursors of prostaglandins, leukotrienes, and thromboxanes with anti-inflammatory, anticoagulant, antiplatelet, and vasodilatory activities (Calder, 2013). On the other hand, the omega-6 fatty acid group plays an important physiological role. It participates in cell membrane structure activities, influencing blood viscosity, blood vessels permeability, antiplatelet action, blood pressure, and platelet functions (Arima & Fukuda, 2011). The principal monounsaturated fatty acid is oleic acid. Studies show that oleic acid-rich diets act beneficially on the lipid profile and may reduce low-density lipoprotein (LDL)-cholesterol level and the incidence of heart disease (Lopez-Huertas, 2010).
Various health benefits have been attributed to the action of carotenoids. They act as antioxidants against cardiovascular diseases, certain cancers, neurological disorders, and macular degeneration related to age and cataracts; they also strengthen the immune system, and act in gene activation and inflammatory processes by modulating the lipoxygenase (Gama & Sylos, 2007).
It has been demonstrated that palm species are promising sources of bioactive compounds and unsaturated fatty acids. However, there is not much nutritional, chemical, and pharmacological information on the use of the bacuri palm Attalea phalerata pulp oil, especially concerning physicochemical properties, and tocopherol and phenolic composition. Therefore, it is essential to investigate and quantify such compounds in the oil extracted from the bacuri palm fruit, focusing on its food or industrial use potential. Accordingly, this study aimed to characterize the bacuri (A. phalerata) pulp through its composition and fatty acid profile, as well as by the physicochemical properties of its oil.
Materials and methods
Plant material
Composite samples comprised of three batches of bacuri fruits from the southeast and midwest regions of the São Paulo state, Brazil, were analyzed in triplicate. After harvesting, whole fruits were washed with distilled water and dried at 40 ºC for 3 h. Subsequently, the pulp was manually separated from the seed with a steel knife. Then, the pulp was dried once more at 40 °C to reduce its moisture content.
Proximate composition of the pulp
The proximate composition of the pulp was established through the following variables: moisture content by dehydration in a vacuum oven at 70 °C, according to method Ca 2d-25 of the American Oil Chemists' Society (AOCS, 2009); ash by calcination at 550 °C, according to method Ba 5a-49 (AOCS, 2009); lipids by Soxhlet extraction with petroleum ether at 40-60 °C, according to method Bc 3-49 (AOCS, 2009); proteins employing the Kjeldahl method, according to method 984.13 of the Association of Official Analytical Chemists (AOAC, 2005), and total carbohydrates and fiber by difference.
Characterization of oil extracted from fruit pulp
The oil used for analysis was obtained from the fruit pulp through extraction with petroleum ether at 40 to 60 °C in the Soxhlet apparatus. The bacuri pulp oil was characterized according to the levels of the following variables: free fatty acid, peroxide value, refractive index at 40 °C, iodine value, saponification value, and oxidative stability, using the Rancimat method (Metrohm Ltd., Herisau, Switzerland) at 110 °C with an airflow rate of 20 L/h, according to method Cd 12b-92 (AOCS, 2009).
Total phenolic compounds
Total phenolic compounds were calculated using the Folin-Ciocalteu reagent and a standard curve of gallic acid, as described by Singleton and Rossi (1965). The blue color produced by the reduction of the Folin-Ciocalteu phenol was measured spectrophotometrically (Shimadzu, Kyoto, Japan) at a wavelength of 765 nm, and expressed as mg of gallic acid equivalents per gram of oil (mg GAE/g). The extraction of phenolic compounds was performed according to the method proposed by Parry et al. (2005).
Total carotenoids analysis
Total carotenoids were determined spectrophotometrically (Shimadzu, Kyoto, Japan) using the method described by Rodriguez-Amaya (1999) for the extraction of carotenoids. Quantification was calculated using absorption values in the maximum absorption wavelength and an A value of 2,592 in petroleum ether. Carotenoids were expressed as β-carotene, in µg/g sample.
Tocopherols composition
The composition of tocopherols was established according to method Ce 8-86 (AOCS, 2009), using a high-performance liquid chromatography (HPLC) system (Varian Inc., Walnut Creek, USA) equipped with a fluorescence detector. The analysis conditions were the following: a silica column of 250 mm x 4.6 mm i.d. with a pore size of 0.5 μm (Varian Inc., Walnut Creek, USA). The system was operated isocratically at a flow rate of 1.2 mL/min. The operating conditions were an λ excitation of 290 nm and an λ emission of 330 nm, and a mobile phase comprised of the mixture of 99.5 % n-hexane and 0.5 % isopropanol. Values were calculated based on the excitation peak area of the reading and expressed in mg/100 g.
Fatty acids composition
Fatty acids composition was determined by chromatography employing a GC 3900 gas chromatographer (Varian Inc., Walnut Creek, USA) equipped with a flame ionization detector (GC-FID) with a split ratio of 1:30, a fused silica capillary column CP-Sil 88 of 60 m of width, an internal diameter of 0.25 mm, and a film thickness of 0.20 μm (Varian Inc., Walnut Creek, USA). The samples were transesterified into methyl esters using potassium hydroxide in methanol and n-hexane, according to method Ce 2-66 (AOCS, 2009). The initial column temperature was 90 °C for 4 min, increasing to 195 °C at 10 °C/min, and then an isothermal procedure was applied for 16 min. The injector temperature was 230 °C, and the detector was 240 °C. The carrier gas was hydrogen. Fatty acids were identified according to the retention times, and quantification was done through the normalized area (%) method. A mixture of 37 esters of fatty acids was used as a standard (Supelco, Bellefonte, USA) from C4:0 to C24:1, with purity between 99.1 and 99.9 %.
Results and discussion
The major constituents of the bacuri pulp were total carbohydrates (41.5 %), lipids (39.2 ± 0.6 %), and proteins (8.5 ± 0.4 %) (table 1). The mineral content, represented by the ash fraction, was also relevant (2.7 ± 0.0 %). Studies carried out with pulps of other palm fruits, such as guariroba (Syagrus oleracea (Mart.) Becc.), macaúba (Acrocomia aculeata (Jacq.) Lodd. ex Mart.), and inajá (Maximiliana maripa (Aubl.) Drude), also presented carbohydrates and lipids as the main constituents, showing their high energy potential (Coimbra & Jorge, 2011; Costa-Singh, 2015). The levels of nutrients from the bacuri pulp were very similar to those found in the freeze-dried açaí (Euterpe oleracea, Mart.) pulp. In a previous study, Menezes et al. (2008) found in açaí pulp, values of 42.53 % for total carbohydrates, 40.75 % for lipids, and 8.13 % for proteins.
Table 1 Proximate composition (%) of bacuri pulp
SD: standard deviation.
Source: Elaborated by the authors
The physicochemical properties of bacuri oil are shown in table 2. The level of free fatty acids was 0.7 ± 0.2 %, and the peroxide value was 1.4 ± 0.0 meq/kg. The low acid and peroxide values recorded, verify the good quality of the bacuri oil related to the development of hydrolytic and oxidative reactions, respectively. The Codex Alimentarius Commission (2009) has defined a maximum acid value of 4.0 mg KOH/g for crude oils and maximum peroxide values of 10 and 15 meq/kg for crude and refined oils, respectively, as quality parameters. The values reported by the bacuri oil are well below these limits, indicating that it is a high-quality raw material and oil.
Table 2 Physicochemical properties of bacuri pulp oil
SD: standard deviation.
Source: Elaborated by the authors
The refractive index and iodine number related to the unsaturation degree of the oil, were 1.463 ± 0.0 and 84.3 ± 1.2 g I2/100 g, respectively. The refractive index and iodine number presented by the bacuri oil are higher than the values of other oils also extracted from palm fruits, including guariroba Syagrus oleracea (1.453 and 70 g I2/100 g, respectively), jerivá, Syagrus romanzoffiana (Cham.) Glassman (1.446 and 69 g I2/100 g, respectively), and macaúba, Acrocomia aculeata (1.455 and 80 g I2/100 g, respectively) (Coimbra & Jorge, 2011). These findings suggest that bacuri pulp oil is more unsaturated than the oils mentioned above.
The saponification number of the bacuri oil was 193.5 ± 1.7 mg KOH/g, similar to most vegetable oils, which have a saponification number between 181 and 265 mg KOH/g. The bacuri pulp oil obtained an unsaponifiable matter content value of 0.50 ± 0.0 %, i.e., below the limit of 1.5 % fixed for cotton, sunflower, soybean, coconut, and olive oils (Codex Alimentarius Commission, 2009).
The oxidative stability index is often a mandatory criterion within the purchasing specifications of food companies while procuring large shipments of oils for food production (Sarkar et al., 2015). The oxidative stability of bacuri pulp oil at 110 °C was 48.7 ± 0.1 h, revealing a high induction period. This value was higher than the one recorded for olive oil, which was 20.9 h (Koprivnjak et al., 2008), as well as compared to other oils also used for cooking, such as soybean and sunflower oils, showing oxidative stability values at 110 °C of 5.85 and 18.83 h, respectively (Sarkar et al., 2015).
Concerning the total phenolic compounds content, bacuri pulp oil recorded 2.4 ± 0.4 mg GAE/g, considered a high value compared with those found in other oils such as soybean, sunflower, corn, canola, and rice, which had total phenolic compound levels ranging from 1.26 to 1.48 mg/100 g (Siger et al., 2008). The levels of total phenolic compounds in guariroba, jerivá, and macaúba pulp oils, were close to the one recorded for the bacuri pulp oil, with values of 2.68, 3.26, and 2.21 mg GAE/g, respectively (Coimbra & Jorge, 2012).
The amount of carotenoids present in the bacuri pulp oil, expressed as β-carotene, was 243.0 ± 2.8 µg/g (table 2). This amount was much higher than those seen in raspberry, blueberry, and blackberry seed oils, ranging from 7.07 to 16.82 µg/g (Parry et al., 2005). Another study showed that the content in corn germ and fiber oils were also lower than the total carotenoids found in the current study, i.e., 5 and 80.1 µg/g, respectively; on the contrary, the value for corn seed oil (324.5 µg/g) was higher (Moreau et al., 2007).
The bacuri pulp oil included only α- and δ-tocopherol (table 3) with a total value of 86.8 ± 0.6 mg/kg, being α-tocopherol the predominant type (86 %). Masson et al. (2008) found similar total tocopherol content (84 mg/kg) in the seed oil of the Chilean palm Jubaea chilensis (Molina) Baill. (Arecaceae), being α-tocopherol also the predominant type, accounting for 45 % of the total value. Generally, higher tocopherol amounts are associated with the unsaturated fatty content in oils (Tuberoso et al., 2007). In this line, some more saturated palm oils showed lower total tocopherol contents than the bacuri pulp oil, including guariroba pulp oil (45.13 mg/kg), guariroba and jerivá kernel oils (19 mg/kg), and macaúba pulp oil (23.10 mg/kg) (Coimbra & Jorge, 2012).
Table 3 Tocopherols (mg/kg) found in bacuri pulp oil
SD: standard deviation.
Source: Elaborated by the authors
The fatty acid composition of bacuri pulp is presented in table 4. The oil proved to be composed mainly of unsaturated fatty acids (78.6 ± 0.1 %), of which 67.3 ± 0.1 % are mono, and 11.3 ± 0.1 % polyunsaturated. Oleic acid was the predominant fatty acid, leading to being classified as monounsaturated with a high content of oleic acid.
Table 4 Fatty acids composition (%) of bacuri pulp oil
SD: standard deviation.
Source: Elaborated by the authors
Among the polyunsaturated fatty acids, linoleic (10.5 ± 0.1 %) and linolenic acids (0.8 ± 0.0 %) stood out; both are considered essential fatty acids. The rate between oleic and linoleic acids was 1/0.2. Among the saturated fatty acids, palmitic was the predominant type (13.3 ± 0.1 %). According to Lima et al. (2017), A. phalerata oil is mainly composed of saturated (20.69 %) and unsaturated fatty acids (78.53%), of which 57.66 % are monounsaturated, and 20.87 % are polyunsaturated. Oleic, linoleic, and palmitic acids are the predominant types.
According to McDonald and Eskin (2007), a good frying oil should have a profile very similar to the one presented by bacuri pulp oil, i.e., low in saturated fatty acids, low in linoleic acid, very low in linolenic acid, and very high in oleic acid. New vegetable oils containing high levels of oleic acid would provide an alternative to the traditional oils commonly used, and ideal as frying oil considering health and stability issues.
Coimbra and Jorge (2012) analyzed the composition of macaúba pulp oil, finding similar results with a predominance of fatty acids, such as oleic (52.5 %), palmitic (24.6 %), and linoleic (13.80 %) acids. In a study carried out by Luzia and Jorge (2013), the main unsaturated fatty acids of Annona crassiflora Mart. (Annonaceae) seed oil were also oleic (49.75 %) and linoleic (16.29 %) acids, while the predominant saturated fatty acid was palmitic acid (18.07 %). According to these authors, this result is consistent with the fact that palmitic acid is the most abundant saturated fatty acid in vegetable lipids.
Comparing the rate between the total saturated and unsaturated fatty acids analyzed in this study with those cited by Borges et al. (2007) for common edible oils such as peanuts, corn, and soybeans, bacuri pulp oil (1/3.7) approached the value found in peanut oil (1/2.8), whereas for soybean oil, this rate was 1/5.7, and for maize, the ratio was 1/6.7.
The composition shown by the bacuri oil (table 4) was very similar to olive oil, providing levels of oleic acid between 55 and 83 %, linoleic acid between 3.5 and 21 %, and linolenic acid of 0.9 % (Codex Alimentarius Commission, 2009). Studies suggest that the beneficial effects of olive oil come from its unique fatty acid profile, characterized by a relatively low level of polyunsaturated and a high level of monounsaturated fatty acids, mainly oleic acid, i.e., the same features recorded for the bacuri oil. Monounsaturated fatty acids, combined with bioactive compounds, can reduce the levels of total and LDL cholesterol, and may protect against the cognitive decline related to age (Schwingshackl & Hoffmann, 2014). A diet rich in monounsaturated fatty acids acts on the resistance to LDL oxidation, metabolic control, and improves the lipid profile (Pérez-Jiménez et al., 2007).
Conclusions
It can be concluded that bacuri pulp is an important source of nutrients, especially carbohydrates and lipids. The bacuri oil was very similar to olive oil with physicochemical properties within the rules stated by the current legislation for vegetable oils. Furthermore, it has good oxidative stability and high contents of phenolic compounds, carotenoids, and monounsaturated fatty acids, mainly oleic acid, demonstrating its potential to become a new source of 'high oleic' oil and bioactive compounds to be used in food preparations, such as salad oil or in margarine formulation.
