Nutritional quality of the seed oil in thirteen Asphodeline species (Xanthorrhoeaceae) from Turkey

G. Zengin^a,*, A. Aktumsek^b, J. Girón-Calle^b, J. Vioque^b and C. Megías^b

^aDepartment of Biology, Science Faculty, Selcuk University, 42250-Konya, Turkey

^bFood Phytochemistry Department. Instituto de la Grasa (C.S.I.C.). Campus Universidad Pablo de Olavide, Edificio 46, Ctra. de Utrera Km 1. 41013-Sevilla. Spain

*Corresponding author: gokhanzengin@selcuk.edu.tr

1. INTRODUCTIONTOP

Asphodeline is an important genus belonging to the Xanthorrhoeaceae family. It includes 14 species and until recently had been classified within the Liliaceae family. Species belonging to Asphodeline are found in the Mediterranean Region, mainly in Middle-Eastern countries. They may be rhizomatous or stoloniferous perennial plants, biennial plants, or annual herbs, and they are found in diverse habitats including river banks, fallow fields, forest clearings, and rocky or clayey slopes. This genus is very well represented in Turkey, where it is known under the names Çiriş otu, Kiriş otu and Yayla çirişi, and includes 20 taxa, 12 of which are endemic (Mathews and Tuzlaci, 1984; Tuzlaci, 1987). Asphodeline taxonomy is complex and most species share similar morphological characteristics (Mathews and Tuzlaci, 1984).

Some Asphodeline species are traditionally used as food and in folk medicine in several countries including Turkey (Tuzlaci, 1985, Lazarova et al., 2009; Todorova et al., 2010). Thus, A. damascena subsp. damascena and A. tenuior subsp. tenuiflora are used to alleviate warts and heal wounds in Anatolian folk medicine. A. cilicica and A. globifera are used for the treatment of earaches and hemorrhoids, respectively (Tuzlaci, 1985). A. cilicica, A. damascena, A. globifera, A. lutea, and A. taurica leaves are consumed in salads in different regions of Turkey. Previous reports show that the protein in Asphodeline leaves has good nutritional properties (Zengin et al., 2012). These leaves are also rich in polyphenols with high antioxidant capacity (Lazarova et al., 2014). Nevertheless, the chemical composition of Asphodeline seeds is largely unknown. Considering that the seeds from vegetables related to Asphodeline including onions are eaten in several countries (Dini et al., 2008), Asphodeline species may well represent an interesting source of nutrients for human consumption. The aims of the present work were to evaluate the nutritional quality of Asphodeline seed oil, and to use the data on fatty acid composition for a cluster analysis in order to build a dendogram showing the relationships within the Asphodeline genera.

2. MATERIALS AND METHODSTOP

2.1. Plant materialsTOP

Asphodeline seeds were collected in different regions of Turkey in 2013 at full maturity. Between five and ten plants were collected from each population. The location and altitude of populations are given in Table 1. Voucher specimens of each taxa were deposited in the KNYA Herbarium at the Department of Biology, Selcuk University, Konya, Turkey.

2.2. Seed oil fatty acid analysisTOP

Extraction of the oil from ground seeds (10 g) was carried out for 6 h using petroleum ether and a Soxhlet apparatus. The solvent was removed using a rotary evaporator. Fatty acid methyl esters (FAME) were produced by saponification using 0,5 N sodium hydroxide in methanol, and transesterified using a 14% BF₃ –methanol solution (IUPAC, 1979). A Gas chromatographic analysis of FAME was carried out using a 6890 N model gas chromatograph equipped with an Agilent autosampler (7683) and a HP-88 capillary column (100 m x 0.25 mm i.d. x 0.2 μm). Helium was used as carrier gas at a 1 mL·min⁻¹ flow rate. The column temperature regime was as follows: 60 °C for 1 min, increase to 190 °C at 20 °C·min⁻¹, 190 °C for 60 min, increase to 220 °C at 1 °C·min⁻¹, and 220 °C for 10 min. The injector and FID detector temperatures were 250 and 280 °C, respectively. The injection volume and split ratio were 1 μL and 40:1, respectively. FAMEs were identified by comparing their retention times with those of FAME standards (Alltech and Accu) and were quantified as percentages of total fatty acids. The results are given as average values of three GC analyses ± SD.

Atherogenic index (AI) and thrombogenicity index (TI) were calculated according to Ulbricht and Southgate (1991) as follows:

AI = [C_12:0 + (4 x C_14:0) + C_16:0] / [(ω6 + ω3) PUFA + C_18:1 + other MUFA]

TI = [C_14:0 + C_16:0 + C_18:0] / [0.5 x C_18:1 + 0.5 x other MUFA + 0.5 x ω6 PUFA + 3 x ω3 PUFA + (ω3 PUFA / ω6 PUFA)].

2.3. Cluster analysisTOP

A cluster analysis was performed using the furthest neighbor method based on a euclidean distance matrix using the Statgraphics 5.1 software.

3. RESULTS AND DISCUSSIONTOP

The oil content in Asphodeline seeds ranged from 0.92% in A. rigidifolia to 4.61% in A. liburnica (Table 2). More than 70% total fatty acids were unsaturated in all taxa (Table 2). The content in polyunsaturated fatty acids (PUFAs) ranged between 48.17% and 68.54% (Table 2). A. tenuior and A. sertachae had the highest and lowest content in UFA, 91.25% and 69.76%, respectively. Saturated fatty acids were found at much lower concentrations, not higher than 30% in any case (Table 2).

The composition in saturated fatty acids, from C_12:0 to C_22:0, is shown in Table 3. Palmitic acid (C_16:0) was the most abundant, although contents were quite variable, from 5.65% in A. tenuior up to 23.69% in A. sertachae. Stearic acid (C_18:0) was found at much lower concentrations, between 1.75% in A. tenuior and 3.72% in A. anatolica. The content of other saturated fatty acids rarely exceeded 1% in any taxa. Consequently, the content in total saturated fatty acids was also quite variable, varying between 8.75% in A. tenuior and 30.24% in A. sertachae. Species with low C_18:0 contents tend to have higher amounts of C_16:0, indicating a negative correlation between the contents in C_16:0 and C_18:0.

Monounsaturated fatty acids from C_14:1 up to C_20:1 were found in the seed oil (Table 4). The most abundant was oleic acid (C_18:1ω9) with contents ranging from 11.34% in A. sertachae to 30.27% in A. tenuior. The isomer C_18:1ω11 was found at lower concentrations. The content in all other monounsaturated fatty acids did not exceeded 1%. Polyunsaturated fatty acids ranged in length and unsaturations from C_18:2 to C_22:5 (Table 5). The essential fatty acid linoleic acid (C_18:2ω6) was the most abundant at contents ranging from 45.04% in A. anatolica to 66.1% in A. taurica. The content in C_18:1 was lower than the content in C_18:2 in all species. The essential linolenic acid (C_18:3ω3) was also relatively abundant in the Asphodeline species, especially in A. globifera, A. sertache, and A. rigidifolia where it was found at 5.36, 4.97, and 4.18%, respectively.

These results on fatty acid composition are in agreement with those reported by other authors in related species. Hence, Yalcin et al. (2014) described the most abundant fatty acid in onion (Allium cepa L.) seed oil as linoleic acid at 49.4 - 60.7%, followed by oleic and palmitic acids. Similar results were found by Reddy et al (2011) and Udayasekhara-Rao (1994), reporting that the most abundant fatty acids in onion seed oil were in decreasing order linoleic acid, oleic acid, palmitic acid, and stearic acid.

As shown in Table 2, the seeds from A. taurica, A. prismatocarpa, and A. damascena have the highest contents in essential fatty acids (EFA), while A. anatolica has the lowest. A. anatolica also has the lowest content in ω6 fatty acids, while A. taurica and A. damascena have the highest. The atherogenic and thrombogenic indexes define the potential of fats and oils to increase cardiovascular risk in humans. A. tenuior and A. damascena have the lowest atherogenic and thrombogenic indexes. These values are similar to those reported for the most popular edible oils, including sunflower, corn, soy, and olive oil (Castro-Bolanos et al., 2005). The highest atherogenic and thrombogenic indexes were found in the oil from A. sertachae, A. rigidifolia and A. anatolica. Hence, from a functional point of view, A. damascena, A. tenuior, and A. taurica have the best seed oil composition. The fact that the leaves from A. damascena and A. taurica are eaten in salads could facilitate the introduction of the seeds from these species in the human diet. Interestingly, the plants that have the worst seed oil fatty acid composition, namely A. anatolica, A. rigidifolia, and A. sertachae, are not used at all for human consumption.

Data on fatty acid composition were used to carry out a cluster analysis of the Asphodeline species. Figure 1 shows the resulting dendrogram, showing that the clusters generated according to fatty acid composition are consistent with the taxonomic classification previously established according to morphological characters (Tuzlaci, 1987). Thus, cluster A includes A. sertachae and A. anatolica, which share the same distribution area in the southern region of Turkey and a poor fatty acid profile from a nutritional point of view. Cluster B includes the three subspecies of A. damascena. In a previous study, A. damascena subspecies were also classified together in a dendrogram that was built according to the amino acid composition of the leaves (Zengin et al., 2012). Hence, these results show that subspecies of A. damascena are also chemically homogeneous. Cluster C, in addition to A. damascena, includes three of the four species belonging to sect. Asphodeline. The fourth species belonging to this section is A. baytopae. Cluster D includes two taxonomically related species, A. rigidifolia and A. globifera, belonging to sect. Appendicigera.

It is concluded that in addition to other parts of the plants, especially leaves but also roots and flowers, the seeds from certain Asphodeline species could represent a good source of essential fatty acids for human nutrition. In fact, onion seeds, which share a similar fatty acid composition with Asphodeline seeds, are used in Indian foods (Yalcin et al., 2014). The use of Asphodeline seeds as a source of nutritious fatty acids would add to the nutritional value of the proteins and polyphenols in the leaves (Zengin et al., 2012; Lazarova et al., 2014).

ACKNOWLEDGMENTSTOP

This work was carried out with the financial support of the Junta de Andalucía (Spain) to the Laboratory of Bioactive and Functional Components of Plant Products (Instituto de la Grasa, C.S.I.C.). Cristina Megias is recipient of a JAE-Doc (C.S.I.C.) contract from the “Junta para la Ampliación de Estudios” program (co-financed by the European Social Fund).

REFERENCESTOP