Triacylglycerols and fatty acids composition of egusi seed oil ( Cucumeropsis Mannii Naudin )

By C. Kapseu * (1), R. Kamga (2) and J.B. Tchatchueng (2) (1) Laboratoire de Thermodynamique Chimique et Appliquee, B.P. 451-54001 Nancy. France. (2) Cameroon National Advanced School of Agro-Industries (ENSAI). P. O. Box 455. Ngaoundere. Cameroon. * To whom correspondence should be addressed. Present Address: Department of Process Engineering. ENSAI. University of Ngaoundere. P. O. Box 455. Ngaoundere. Cameroon.


Triacylglycerols and fatty acids composition of egusi seed oil {Cucumeropsis Mannii Naudin)
Triacylglycerols were determined from a Cameroonian (African) white egusi seed oil {Cucumeropsis Mannii Naudin) using reversed phase high performance liquid chromatography.The fatty acid composition of two types of seed (red and white) is obtained by capillary gas chromatography.The study of the triacyiglycerol composition obtained in white egusi seed oil revealed that only nine triacylglycerols were present in amounts above 1% (area).The first five triglycerides represent more than 80% of the total triacylglycerols, and the major triacyiglycerol was palmitoyldilinoleoylglycerol, accounting for 23.6% of the oil.This oil contains a high proportion of linoleic acid (60% wt/wt).
In this paper, we report the use of reversed phase high performance liquid chromatography for the triacylglycerols separation of egusi seed oil.The fatty acids composition of two cultivars is determined by capillary gas chromatography.

INTRODUCTION
The egusi plant (Cucumeropsis Mannii Naudin) belongs to the cucurbitaceae family.This plant is grown especially for its seeds.These seeds are consumed by the populations from tropical countries (1).Concerning Cameroon, the foods from these seeds are well appreciated.Studies on All the samples of extracted egusi seed oil were done in duplicate for each experiment.The samples were stored in freeze dryer before run on chromatograph.

RP-HPLC
Crude egusi oil is obtained from white seed grown in Western Cameroon.The extraction is conducted according to iUPAC method (8).The triacylglycerols were determined by reversed phase high performance liquid chromatography.The materials and methods used have been detailed in a previous publication (9).It can be recalled that the mobile phase acetone/acetonitrile (63/37 v/v) is used.Chromatogram is obtained using the following equipment: LC-6A pump (Shimadzou, Japan); Rheodyne loop injector model 7125; refracto-detector (Chromatofield, France); a series of two LC-18 Supelcosil columns, 5 |i, 150 mm x 4,6 mm I.D. (Supeico, France).The quantitative analysis is performed by using a Spectra-Physics integrator, model SP 4290.
The triacylglycerols (TG) are separated according to their partition nunnber (PN).This number is defined as carbons number minus two times the double bonds (10).However, this method did not allow distinguishing triacylglycerol isomers in position 1,3 or 1,2.Then, the triacylglycerols such as POS, SOP, PSO, OSP, OPS, and SPO are the same as regards the notations.
The identification of the peaks was performed using RP-HPLC chromatogram profile of weliknown oil as cottonseed and the triglycerides standard purchased from Sigma (MO, USA).
The theoretical calculations of triglycerides composition is obtained from the experimental values of fatty acids according to 1,3 random, 2-random distribution model (12).

Gas Chromatography
The oil content of two egusi cultivars seed purchased at the Dang-Ngaoundere (Cameroon) market is obtained according to AOAC method (11).The two cultivars are different by the color of their shell and seed (red or white).The fatty acid composition of these samples is obtained by capillary gas chromatography (GC).The method used has been described by Sukhija and Palmquist (13).
Fatty acid analysis was done on a Hewlett-Packard 5890A gas chromatograph fitted with automatic sampler 7673A and FID detector.Conditions: 10 % SP-2340 fused silica capillary column (0.32 mm ID; 30 m length) (SupeIco, Inc., Bellefonte, PA), temperature programmed from 160°C to 180°C at 3°C/min; Initial time was 10 min and final time was 20 min; Injector and detector temperature at 220°C, air flow at 300-400 mL/min, hydrogen at 30 mL/min and nitrogen flow at 0.5 m[_/min; split ratio was 100:1.
The reports generated by GC were entered into a HP microcomputer model Vectra QS/IGS.The chromatogragh was displayed on a HP video graphic color and the data were printed by a HP Deskjet 500.
Identifications were based on GC retention times of known compounds and their comparison with that of the internal standard.
The fatty acids of white egusi seed oil is also obtained by calculations from experimental triacylglycerols composition.The mathematical method have been described earlier (14).

Repeatability of the method
To determine the repeatability of the method, the same sample of crude oil was chromatographed three times for the RP-HPLC and four times for the GC, obtaining a variation coefficient for the triacylglycerol and fatty acid composition less than 6.The data presented here are the mean values.

RESULTS AND DISCUSSION
Figure 1 shows the chromatogram of white egusi seed oil containing 15 peaks with five important ones which represent more than 80% of the total triacylglycerols (Table I).The experimental results are compared to theoretical composition obtained from capillary fatty acids.It is observed (experiment) that palmitoyldilinoleoylglycerol (PLL) has the highest proportion.Minutes Fig. 1 RP-HPLC chromatogram of white egusi seed oil.
The fatty acid composition and oil content of two egusi cultivars seed are shown in Table II.The fatty acid composition of white egusi seed oil is compared to the theoretical value obtained from experimental triacylglycerols composition (table I).
The results suggest that the oil content as well as the total fatty acid vary according to the cultivar.The red cultivar contains slighly more oil and total fatty acid than the white one.The fatty acid profile of the two cultivars did not show any appreciable variation.However the red cultivar is richer in unsaturated fatty acids (77%) than the white cultivar (72,4%).This is the reverse tendency for saturated fatty acids with respectively 22.7 and 27.1% for red and white cultivars.
The percentages of fatty acids in white egusi seed oil is similar to those published by Badifu (1).Our analysis shows the presence of small amount of fatty acids like palmitoleic, linolenic and arachidic acids which Badifu method did not detected.The fatty acids over 20 carbons are absent from egusi seed oil.Egusi seed oil fatty acids data can be compared to those published by Tsuyuki et al (7) on pumpkin seed oil (Cucúrbita moschata).
In spite of similar RP-HPLC chromatogram profile of sunflower (15) (16) (17) and egusi seed oils, triacylglycerols and fatty acids have proportions differing in each oil.The two oils are particularly rich in linoleic add.Contrary to the cottonseed cake which contains a toxic component called gossypol (18), egusi seed cake is a good foodstuff for the population.Egusi seed appears to be a source of linoleic acid and may constitute a useful product with good nutritional value.