Proximate composition of Turkish sesame seeds and characterization of their oils

Se ha evaluado la composición proximal de cuatro variedades de semillas de sésamo de Turquía así como el aceite obtenido mediante extracción en frío con hexano (composición en ácidos grasos, triglicéridos y esteroles). Las composiciones medias de las semillas fueron similares para todas las muestras siendo los valores medios 4,40%, 4,41%, 21,00%, 54,26% para humedad, cenizas, proteínas y aceite, respectivamente. Los ácidos oleico y linoleico fueron los ácidos grasos mayoritarios mientras los ácidos palmítico y estearico fueron los principales ácidos saturados. Los triglicéridos mayoritarios, determinados mediante HPLC fueron LOL; LOO; PLO; LLL y OOO, suponiendo un 62,45% del porcentaje total de los triglicéridos. Los esteroles mayoritarios fueron β-sitosterol, campesterol, estigmasterol, y -5, avenasterol, identificándose también pequeñas cantidades de colesterol, clerosterol 5,24 estigmastedienol, -7 estigmastenol y avenasterol.


INTRODUCTION
Sesame seeds (Sesamum Indicum, L.) are one of the world's most important and oldest oilseed crops known to man (Garbia-Abau et al., 2000).Sesame, also known as sesamum, gingelly, benissed, sim-sim and till is an important annual oilseed crop.It has been cultivated for centuries, particularly in Asia and Africa, for it is high content in edible oil and protein.India, China, Sudan and Burma are the major producers of sesame seeds by contributing to approximately 60% of its total world production.Most of the sesame seeds are used for extraction and production of oil.The oil has a mild odor and pleasant taste and as such, is a natural salad oil requiring little or no winterization.It is a cooking oil in the form of shortening and margarine, as a soap fat in pharmaceuticals and as a synergist for insecticides, (Garbia-Abau et al., 2000).
A lot of sesame varieties and ecotypes which have been grown for hundreds of years are distributed in various ecological regions of Turkey (Baydar et al., 1999).Sesame cultivating in Turkey is most widespread in places influenced by a Mediterrenean climate with approximately 80.000ha.The use of improved breeding varieties in production is very limited because hundreds of local varieties and their ecotypes have adapted well to their own spesific conditions, (Baydar et al., 1999).Today, maintenance of local varieties plays a large role in preventing the loss of genetic variability in Turkish sesame populations.However, new commercial varieties may replace the local varieties in the near future (Baydar et al., 1999).The average anual production of sesame seeds in Turkey is 33.000 ton/year (Anon, 1999).
The objective of this study was to investigate the chemical composition of certain Turkish sesame seed varieties and their oils.

Oil Extraction
Sesame seed oil was extracted with hexane at 20 °C for 72 hours; then filtered .This process was repeated three times using fresh solvent each time in order to extract most of the oil from sesame seeds.Miscella was collected, mixed and evaporated at 50 °C under vacuum.Then the extracted oil was dried using anhydrous sodium sulphate.

Analytical Determinations
Protein and ash content were determined according to AOCS methods, 5-38 and 5-49 (AOCS, 1989).Crude protein was calculated using a nitrogen conversion factor of 6,25.Moisture and oil content of sesame seeds were determined according to IUPAC 1. 121-1.122. methods, respectively (IUPAC, 1979).The fatty acid methyl esters of lipids were prepared according to the AOAC method 991.39 (AOAC, 1980).
The analyses of fatty acid methyl esters were carried out with a Hewlett Packard Gas Chromatograph (model 5890) equipped with a hydrogen flame ionization detector and a capillary column; CP-Sil-88 Wcott fused silica (50mx0.25mmid., of 0.20mm film tickness).The temperatures of injector and detector were 270 °C.The initial column temperature was 170 °C., and then raised to 205 °C at a rate of 1 °C/min.Split ratio was 1/50.The carrier gas was hydrogen at a flow rate of 1ml/min.The identification and quantification of fatty acid methyl esters was accomplished by comparing retention times of the peaks with those of standards.The unsaponifiable matter was extracted after saponification of oil according to the standard method IUPAC 2.403 (IUPAC, 1979).The unsaponifiable matter was separated on TLC plates (20x20) precoated with silicagel 60 (0.300mm).Elution was performed using benzen-aceton (95/5) as the mobile phase.The identification of the various compounds in the different unsaponifiable samples was achieved by comparison of their R f values with reference standards as described by Paganuzzi and Leoni (1979).Sterol fraction was silylilated according to Boven et al. (1997).Bis, trimethylsilyl-trifluoroacetamide (BSTFA) and trimethyl-chloro-silan were used for the sylilation procedure.The analysis of triacylglycerols (TAG) was performed according to the method proposed by the International Olive Oil Council (IOOC) (Anon, 1991).HPLC separations of TAG were conducted using a Lichrosphere 100 column (250x4.0mm,id).The elution solvent was at 1mL/min acetone/acetonitril (70/30,v/v) at ambient temperature.The instrument used was a Hewlett Packard Model 1050 liquid chromatography equipped with a refractive index detector.Separated triacylglycerols as a function of equivalent carbon number (ECN) were identified using reference triglycerides and relative percentages were calculated automatically.

RESULTS AND DISCUSSION
The proximate chemical composition and fatty acid profile of Turkish sesame seeds and oils are presented in tables 1 and 2.
The moisture contents found for the four varieties of sesame seeds from different regions of Turkey were between 4.16% and 4.62% with a marginal difference of 0.46%.According to these results there are no significant differences due to variety in the moisture content of sesame seeds.Bahkali et al. (1993) reported that the moisture content of different cultivars from different countries was in the range of 3.65-5.60%,which is in good agreement with these results.These values (4.16%-4,62%) are also similar to the values reported (4.12%-4.73%)by Dashak and Fali (1998).
Muganlı (Menemen) being the variety with the lowest content (50.57%).The economic value of sesame seeds is dependent on its oil content rather than its protein content.Bahkali et al.(1998) reported that the oil content of Saudi and Indian sesame seeds ranged from 43.2% to 54.0%, a lower content than that found for Turkish sesame seeds.Baydar at al. (1999) also reported that oil content in the Turkish sesame seeds of the TSP 933749 line selected from the TSP 9337 population was found to be 63.25% which was significantly higher than the content of Indian, Lebanes and Saudi sesame varieties (Bahkali et al.1998).
Fatty acid compositions of the oils extracted are shown in Table 2.As can be observed, there are no significant differences between the varieties and oleic and linoleic acids are the main constituents accounting for more than 80.0% of the total fatty acids.Similar percentages were found for both fatty acids, the mean values being 42.74 and 41.55%, respectively.
The distribution of triacylglycerols in sesame seed oils are given in table 3. Eleven TAG species