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Introduction
American oil palm (Elaeis oleifera H.B.K. Cortés) has become a strategic genetic resource due to its outstanding morphologic and physiological characteristics as slow growth, tolerance to common pests and diseases for African oil palm, oil with high content of unsaturated fatty acids, and substantial amounts of carotenes and vitamin E (Rivera, Cayón & López, 2013). An important trait that E. oleifera processes is its hybridization capacity to form interspecific hybrids with the African oil palm Elaeis guineensis; these OxG hybrids produce oil with larger quantities of unsaturated fatty acids, carotenes and vitamin E compared to the highly commercial African oil palm (Guerrero, Bastidas & García, 2011).
For the above-mentioned reasons, OxG hybrids are the only economically viable alternative in those regions where the spear rot (SR) disease is lethal, and according to Suárez, Cayón & Ochoa (2013); furthermore, with an effective and permanent assisted pollination, the hybrids can achieve yields of 35 t.ha-1 and an industrial extraction rate of 20-21 %.
A study carried out by Choo, Ma & Yap (1997), found that raw oil extracted from African palm oil has the following compound concentrations: vitamin E ranging from 600-1000 ppm, carotenes between 500-700 ppm, and sterols between 250-620 ppm. Moreover, squalene values range from 200-600 ppm and coenzyme Q concentration between 10-80 ppm; the results showed that vitamin E is the most abundant substance found in palm oil, and is one of the four essential vitamins for human body.
On the other hand, studies carried out by Hazir, Shariff & Amiruddin (2012), and Singh, Tan, Panandam, Rahman, Ooi, Low, Sharma, Jansen & Cheah (2009), found that raw oil obtained from E. oleifera has high levels of oleic and linoleic acids, but low levels of palmitic acid, and in top of this, it also has other saturated fatty acids, similar in composition to olive oil.
In addition, the carotene content of this oil is very high (4300-4600 ppm) and is comprised by a and β-carotenes, including cis and trans forms. Therefore, it also has small quantities of non-cyclic (lycopene, phytofluene, phytoene and neurosporene), and cyclic carotenes (a and β-carotenes with zeaxanthin), and lutein, most of them precursors of vitamin A (Ping, 2006; Tranbarger, Dussert, Joet, Argout, Summo, Champion, Cros, Omore, Nouy & Morcillo, 2011).
When analyzing oil extracted from OxG hybrids, Rincón, Hormaza, Moreno, Prada, Portillo, García & Romero (2013), found that it is an important source of carotenoids (820 mg.kg-1), vitamin E Physicochemical characterization of bunches from American oil palm (Elaeis oleifera H.B.K. Cortes) and their hybrids with African oil palm (Elaeis guineensis Jacq.) (1316 mg.kg-1) and phytosterols (941 mg.kg-1). Tocotrienols constitute 81-85 % of the total vitamin E content, β-carotene 73 % of the total carotenoids content, and β-sitosterol 63% of the phytosterol content. Furthermore, Rasid, Parveez, Ho, Sambanthamurthi & Napis (2009), found that OxG hybrids have intermediate carotene content, i.e. superior to values found in E. guineensis and lower than the ones found in E. oleifera. Moreover, vitamin E compound as tocotrienols and tocopherols have antioxidant properties, which have allowed catching damage of free radicals responsible for numerous degenerative cardiovascular diseases as arteriosclerosis or arthritis, cancer and premature aging (Rocha, Prada, Rey & Ayala, 2006).
Given these concerns, the aim of this study was to establish and compare the physicochemical characteristics of bunches and the quality and composition of their oils from five palm materials of E. oleifera and three interspecific hybrids of E. oleifera x E. guineensis. This information will provide tools to select mother parents of E. oleifera for breeding new hybrid materials of commercial interest; moreover, this will allow giving solution alternatives to problems that are currently being associated to the oil palm agroindustry in Colombia.
Materials and methods
Study site
The research was carried out in the Indupalma Ltda. plantation located at10°20' N and 73°11'W in the municipality of San Alberto, Cesar department of Colombia, at an altitude of 125 m.a.s.l., maximum temperature of 34°C and minimum of 22°C, relative humidity of 72.3%, annual rainfall of 2497 mm, annual evaporation of 1208 mm, and 2130 hours of solar brightness per year.
Agroecological conditions of the site corresponds to Tropical Moist Forest according to life zones stated by Holdridge.
Plant material
Eight palm materials, i.e. five American palm genotypes and three OxG hybrids of different ages were the plant material used in this study (Table 1).
Physicochemical variables measured
The physical analysis of bunches was carried out using the methodology described by García & Yáñez (2000). Removal and cleaning of normal, partenocarpic and abortive fruits from all genotypes was carried out and their bracts were then cut off; these were then counted, weighed and data was registered. The average fruit weight and number as well as number of rachilae were registered. Fruit sample comprised 30 fruits with an average weight between 250-300 g. Normal fruits were pulped manually until the nut was completely clean. Then the nuts were cleaned and weighed, and by difference, the weight of mesocarp was established.
When establishing the amount of mesocarp in partenocarpic fruits, 30 fruits were selected without kernel and without nut sign; once these were pulped the sample was homogenized; this same procedure was carried out for normal fruits. In both cases, the mesocarp sample was dried in an electric oven; then the oil content was established with a Soxhlet system. To establish the shell/kernel relation in normal fruits, nuts stemming from 30 fruits were placed in a drying recipient and were then taken to the oven during the whole night at 105°C. Next day these were taken out and left to cool down at room temperature, where they cut and the kernel was removed completely, collecting the shell and weighing it.
The chemical analyses of fatty acid, vitamin E and carotenes content were carried out in the oil laboratory of Centro Experimental La Vizcaína of Cenipalma. The fatty acid profiles of the oil samples were carried out according to the AOCS (1994) standards, and establishing the methyl esters of fatty acids with gas chromatography using a flame ionization detector. Oil samples were saponified using KOH/MeOH. Fatty acids were derived to esters using a BF3 in methanol solution. The esters were extracted and 1 μL was injected to the chromatographic system. The equipment used was a gas chromatograph 7890 A (Agilent Technologies, Wilmington, USA). The column employed in the analysis was a DB-23 (J&W Scientific, Cat. 122-2362) 60 m x 0.25 mm D.I. x 0.25 μπι f.e., and the injection was carried out in split mode (50:1). Hydrogen was used as the carrier gas at a constant flow of 33 cm.s-1. As a reference pattern for the retention time periods, a SupelcoTM 37 component FAME mix (Supelco, Bellefonte, PA, Cat No 47885-U) mixture was employed.
Methyl esters in fatty acids were identified by comparison with the retention times of the standard mixture, analyzed under the same chromatographic conditions; further, quantification was carried out with the normalization of areas method. The results are expressed in mass to mass (m.m-1) percentage according to the official AOCS method Ce 1-62 (AOCS, 1997).
The vitamin E analysis (i.e. tocotrienols and tocopherols) was carried out through high performance liquid chromatography (HPLC), using a fluorescence detector and a Merck Chromolith RP-18e column (Prada, Ayala-Diaz, Delgado, Ruiz, & Romero, 2011). To quantify tocopherols and tocotrienols an external standard method was used employing the certified patterns CALBIOCHEM (Tocotrienol Set Cat. No. 613432), and CALBIOCHEM (Tocopherol Set Cat. No. 613424).
Carotene analysis (i.e. α-carotene and β-carotene) was carried out with a HPLC, using the ultraviolet ray detector in the visible region; a Merck Chromolith RP-18e column was used according to Rodríguez (1999). Quantification was carried out using an external standard method and using as a calibration pattern β-carotene at 97% (Sigma-Aldrich C-4582).
The physicochemical variables established with their respective abbreviations can be seen in Table 2.
Statistical analysis
A completely randomized experimental design with three replicates was carried out with three bunches per replicate. Nine bunches were harvested randomly from each palm material that stemmed from inflorescences without assisted pollination, and with perimeter presence of E. guineensis.
Data was analyzed through an analysis of variance and averages of the physical analysis variables of the bunch components were compared with Duncan's multiple range test using the SAS® 9.2 software. To establish fatty acids, vitamin E and carotenes profile a descriptive analysis was carried out to construct stacked bar figures.
Results
Physical analysis
Materials A, C and hybrid II showed the highest fruit set (FS) values (Figure 1a). Regarding red partenocarpic fruits from bunches (RPFB), materials A and hybrids II and III showed the highest values, and differed significantly from materials B and D (Figure 1b). Moreover, the highest abortive fruits per bunch (AFB) values were found in inflorescences whose pollination was not assisted. These materials stemmed from E. oleifera D material and hybrids I and III while the lowest values were found in the materials C, A, and hybrid II.
Regarding average weight of normal fruits (AWNF), materials B, D, and hybrids I and III showed significantly higher values. In the case of average weight of red partenocarpic fruits (AWRPF), the behavior of the genotypes was similar among these (Figure 1c).
Figure 1 Physical variables measured in American palm bunches (A, B, C, D and E) and their interspecific hybrids OxG (I, II and III), a) FS; b) NFB, RPFB, and AFB; c) AWNF, AWRPF; d) MNF), ENF, and ESNF. The vertical lines over the bars show the standard error; averages with the same letter do not show significant differences according to the Duncan test, p < .05, n = 8.
For percentage of mesocarp found in normal fruits (MNF), hybrid materials showed the highest values, of which hybrids II and III did not show significant differences between each other. Likewise, hybrids II and I did not differ statistically among each other, but showed significant statistical differences with E. oleifera materials. Regarding percentage of endocarp in normal fruits (ENF), all hybrid materials registered significantly lower values compared to the American materials. Regarding percentage of endosperm in normal fruits (ESNF), materials A, B, D and E differed significantly from hybrid material III, that shows a lower value (Figure 1d).
The hybrid materials I, II and III showed the highest percentage of mesocarp for red partenocarpic fruits (MRPF) values with significant differences found in E. oleifera materials (Figure 2a). Figure 2b shows that E. oleifera A, C, E and hybrid I materials showed higher humidity percentages in normal fruits in bunches (NFB).
Regarding percentage of oil in pulp of normal fruits (OPNF), hybrid materials II and III showed significantly superior values compared to other genotypes. E. oleifera Coarí genotype showed outstanding percentage of oil from normal fruits in bunches (OBNF).
In Figure 2c, the humidity percentage in red partenocarpic fruits (HRPF) was significantly higher in material D compared to the others. Percentage of oil from pulp and bunches in red partenocarpic fruits (OPRPF and ARFPR) were superior in hybrids compared to all E. oleifera materials; nevertheless, hybrids II and III showed significantly different averages compared to other materials.
Figure 2 Physical variables measured for bunches of E. oleifera and their interspecific OxG hybrids (I, II and III), a) MRPF; b) HNF, OPNF and OBNF; c) HRPF, OPRPF, and OBRPF; and d) OHP, and OEP. The vertical lines over the bars show the standard error; averages with the same letter do not show significant differences according to the Duncan test, p < .05, n = 8.
This is however logic, as OBRPF is a product of OPRPF. Percentage of oil in humid pulp (OHP) and percentage of oil extraction potential (OEP) are presented in Figure 2d; these values were superior in all hybrids compared to E. oleifera materials.
It is important to highlight that hybrid II and III showed the highest OPNF and OPRPF values that indisputably is reflected in the highest OEP values.
Chemical analysis
Fatty acids profile
Fatty acid profiles of the oil extracted from materials assessed are shown in Table 3.
Table 3 Fattyacids profile (in percentage) ofthe oil extracted from E. oleífera and its interspecific OxG hybrids
Regarding palmitic acid (main saturated fatty acid of the profile), B material outstood with the highest content, and C material showed the lowest content. Among the intraspecific crosses of E. oleifera (OxO), D material showed the highest palmitic acid value compared to the E material, tendency that was among interspecific hybrids (OxG); moreover, hybrid I was the material with the highest palmitic acid value, and hybrid II showed the lowest value.
The highest oleic acid values were reported in E. oleifera Sinú genotypes and in hybrid II, and the lowest in A, B, and hybrid I. In total unsaturated fatty acids, E. oleifera materials were superior compared to the OxG hybrids.
Vitamin E and carotenes
Total vitamin E and carotenes content of oil extracted from the material studied is shown in Table 4. It is apparent that hybrids, especially hybrid I and II, showed significantly higher vitamin E as well as other components compared with E. oleifera materials. Material C and all hybrids showed the highest carotene contents, i.e. a-and β-carotene.
Discussion Physical analysis
A good behavior of the genotypes Coarí and Sinú as well as hybrid II in relation to FS is explained by the fact that the last two materials have a higher degree of natural pollination by insects. This is because Sinú genotype is native to the region, and therefore, its pollen viability is higher than 80%, guaranteeing good bunch formation (Rivera et al., 2013). Furthermore, the Coarí genotype, due to its age, is better adapted; thus, hybrid material of these two E. oleifera sources achieve better natural fructification.
In the case of AFB, the highest values were found in E. oleifera material D and hybrids I and III. This suggests that when working with the Coarí genotype, it is of utmost importance to carry out assisted pollination; if this labor is not carried out losses in oil extraction potential in OxG hybrids that are commercially used, will occur. AWNF of materials B, D, and hybrids I and III were signifi cantly higher because these materials have endosperm, shell and mesocarp in their fruits, compared to partenocarpic fruits that only have mesocarp.
The highest MNF values in OxG hybrids can be explained by the contribution of E. guineensis var. pisifera as the male parent in hybrids. MNF values in E. oleifera materials ranged from 46.7-51.84 % similar to the one reported by Rey, Gomez, Ayala, Delgado & Rocha (2004), i.e. 30.5-54.7 % in E. oleifera palms harvested in Cenipalma.
In like manner, the fact that the three hybrid materials showed the highest MRPF values just as the results for MNF shown above, this probably also obeys to genetic contributions from E. guineensis var. pisifera as the male parent in interspecific OxG hybrids. The variation among studied genotypes for humidity traits in normal fruits (HNF) could been affected by relative humi dity conditions or rainfall during harvest. In the case of OPNF, a good behavior shown by hybrids II and III is coherent with the lower HNF values for these two materials; this indicates that in mesocarps of normal fruits, there is a higher oil content compared to the water content; this is na mely an important agronomic characteristic from an industrial point of view. In addition, OBNF is a fundamental characteristic that expresses the total oil production percentage per bunch that guarantees higher oil extraction percentage in palms, finding in this study that E. oleifera Coarí genotype was outstanding.
The superior traits of hybrids compared to E. oleifera materials in variables OPRPF, OBRPF, OHP and OEP is due to genetic inputs of E. gui-neensis as a male parent. However, data found in this research were higher to the ones reported by Rey et al. (2004), in E. oleifera from the genetic collection stored in Cenipalma.
Chemical analysis Fatty acids profile
Cadena, Prada, Perea & Romero (2012), described the fatty acid profile finding a superior palmitic acid values in E. guineensis materials (Dura Angola-type with 40.87 % and Tenera-type with 40.69 %) compared to its OxG hybrid (30.19 %) and E. oleifera (29.5 7 %). However, Rivera et al. (2013), found similar values to the ones shown in this study, where the contents of palmitic acid were higher in hybrid OxG materials compared to E. oleifera materials. Choo et al. (1997) also found similar values to the ones found in our study, reporting a palmitic acid content of 28.2 % in a hybrid OxG material, and 18.7 % in E. oleifera material.
The oleic acid content of the E. oleifera Sinú genotype can be highlighted due to its high con centration, character that is transferred to hybrid II. On the contrary, for a-linolenic acid that is also high in E. oleifera Sinú genotype, this has not been the case, as this trait has not been transfe rred to hybrid II combination. A study carried out by Mondragón & Cuellar (2011), reported values slightly superior to the ones found in this study.
The aforementioned behavior suggests that E. oleifera parent provides the good oil quality trait found in hybrids, especially due to their unsaturated fatty acids content. Linoleic acid from the American materials in this study ran ged between 10.6-18.3 %, and from 9.9-13 % for hybrid materials. In this respect, Mondragón & Cuellar (2011), found values of 21.1 %, which are superior to the ones found for this acid in American oil palms, but similar for hybrid palms.
The results of this study agree with the ones found by Rey, Gomez, Ayala, Delgado & Rocha (2004), who found that the materials of E. oleifera have in general, better unsaturated fatty acids characteristics (68-74%), in comparison to an interspecific hybrid (64%) and to E. guineensis (49-53%) material. Similarly, Rivera et al. (2013), also described higher values for E. oleifera ma terials compares to the OxG hybrids that are similar to the results found in this study. The very low values of the other fatty acids found in oil samples, confirms the low importance that these have in oil palm composition.
Vitamin E and carotenes
In this study, hybrid materials showed higher vitamin E value, including their components, compared to materials of E. oleifera. These results agree with the ones published by Rey et al. (2004) who described a hybrid material with a superior vitamin E content (1338 ppm) compared to E. oleifera (519-1140 ppm) material. On the other hand, Cadena et al. (2012), reported an opposite result, as total vitamin E content was superior in E. oleifera (1989 ppm) material compared to hybrid material (965 ppm).
In relation to carotenes content, Sinú geno type and all hybrids showed the highest total carotenes content, including a- and β-carotenes contents. This is consistent with results carried out by Cadena et al. (2012), and Rey et al. (2004).
Moreover, due to the variation in quality and production of bunches found among parental po pulations of E. oleifera and their interspecific hy brids with E. guineensis when the physicochemi-cal characterization of palm bunches was carried out, this gives some insight in the agronomical potential of the OxG hybrids for development of oil palm culture in Colombia. This is especially important regarding tolerance potential of oil palm to lethal diseases in America. Furthermo re, this research provides valuable input to the knowledge in oil palm breeding that we expect to be of great use for the public and private sectors.
Conclusions
In this study, the best fruit set values were found in the E. oleifera Coarí and Sinú genotypes and their hybrid combination, as they are native materials with good adaptation and reproductive traits. However, care has to be taken with the Coarí genotype when combined with other plant material to carry out assisted pollination and avoid losses in oil extraction potential.
Interspecific OxG hybrids showed outstanding traits in percentage of oil and oil extraction, as well as in percentage of mesocarp in normal as well as in partenocarpic fruits, compared to other plant materials probably due to genetic inputs of E. guineensis as the male parent.
Hybrids II and II showed important oil percen tage values with low humidity percentage that is an important agronomic trait from an industrial point of view. However, considering traits that guarantees higher oil extraction percentage, E. oleifera Coarí genotype showed the best values.
Although hybrid materials showed higher va lues in some components of the fatty acid profile as well as in vitamin E content, the parent E. oleifera is the one that provides good oil quality trait found in these hybrids.
Physicochemical characterization of palm bunches carried out in this study suggests that there is an important variation among parental populations of Elaeis oleifera and their interspe cific hybrids with Elaeis guineensis, due to the quality and production of bunches.
