Chemical Characterization and Edibility of the Oil Extracted from Citrullus colocynthis Seeds W. N. SAWAYA, N. J. DAGHIR, and P. KHAN ABSTRACT The characteristics and composition of the crude oil extracted from Citrullus colocynthis seeds were examined. Data obtained for the iodine value, saponification number, Reichert-Meissl and others compare well with other edible oils. Thin-layer chromatography in conjunction with gas-liquid chromatography-mass spectrometry revealed over 75% degree of unsaturation major among which were linoleic, 50.6% and oleic acids, 25%. Upon storage, the oil showed relatively low peroxide values that were within the acceptable limits set for other vegetable oils. Animal experimentation trials on the oil using chicks as the experimental animals did not show any toxicity effects. Based on these results, C’itrdlus colocynthis oil might be of some potential use for animal feed and/or human consumption. INTRODUCTION Citrullus colocynthis belongs to the Cucurbitaceae or squash family which produces seeds rich in oil and protein. It is believed that the plant is native to Africa and the Middle East and is probably an ancestral type of the water- melon (Curtis, 1969). It is a long-lived perennial and grows wild in deserts under extreme xerophitic conditions. Young fruits are fleshy, mottled with dark-green and usually turn yellow when ripe (Tackholm, 1974). They are extremely bitter in taste and are full of smooth and shiny seeds which are thought to be rich in oil and protein. Several cucurbit oils are currently used for cooking in countries other than the United States (Curtis, 1946, 1948; Girgis and Said, 1968). Data on the utilization of various cucurbit seeds is extensive in the literature including seeds of Cucurbita foetidissima Curtis, 1946; Bemis et al., 1967; Shahani et al., 1951; Hensarling et al., 1973; Jacks et al., 1972; Bemis et al., 1975), C. digitata and C. palmitata (Ault et al., 1947; Bolley et at., 1958). Apadanthera undulata (Bemis et al., 1967) and C. peppo (Curtis, 1948; Jacks et al., 1972; Alekseeva, 1950). However, incomplete and sometimes controversial data are reported on Citrullus colocynthis seed oil. In the present investigation, an attempt was made to study the chemical characterization and suitability of the oil extracted from the seeds of Citrullus colocynthis plants grown in the Kingdom of Saudi Arabia for animal feed and/or human consumption. MATERIALS&METHODS Preparation of the oil Wild citrullus colocynthis gourds were collected from the vicinity of Riyadh city, Saudi Arabia. The dried fruits were crushed by hand and the seeds separated. The seedswere then ground into powder by a Wiley mill (Model 4, Philadelphia, PA) using 2.0 mm sieve. 120g of the ground seeds were extracted for 36 hr with hexane in a soxhlet extractor. After extraction of the oil the solvent Author Sawaya and Khan are with the Food Science & Nutrition Section, Regional Agriculture and Water Research Center, Ministry of Agriculture and Water, P.O. Box 17285. Riyadh. Saudi Arabia. Author Daghir is affiliated with the Animal Science Dept., American Univ. of Beirut, Beirut, Lebanon. 104-JOURNAL OF FOOD SCIENCE-Volume 48 (19831 was evaporated under reduced pressure by using a rotary evaporator. The oil obtained was kept under nitrogen in sealed aluminum foil- wrapped bottles under refrigeration for further analyses. Chemical analysis of oil All chemical analyses including acid value, iodine number, saponification value, Hehner value, Reichert-Meissl number, and unsaponifiable matter were determined according to procedures outlined in AOAC (1980). Refractive index was determined by an Abbe refractometer with temperature adjustment (American Opti- cal, Model 10450). Isolation and identification of fatty acids The extracted oil was dissolved in chloroform and subjected to analytical and preparative thin-layer chromatography (TLC) on silica gel GF plates (0.5 mm and 1 mm respectively) with petroleum etherdiethyl ether-acetic acid (75 : 24.5 :0.5, v/v) as solvent system. The components were visualized under ultraviolet light after spraying the plates with a 0.1% ethanolic solution of 2’,7’dichlorofluorescein and were identified by comparing their Rf values with those of known standards. For the preparation of the methyl esters, 2g of the oil was treated with 0.5N methanolic NaOH and refluxed with 15 ml of a 14% solution of BF3 in methanol and 5 ml benzene for 12-16 min AOAC (1980). After extraction with chloroform or ethyl ether, the extract was dried with anhydrous sodium sulfate and evaporated to dryness under reduced pressure.The methyl esters were separatedby thin-layer chromatography on silica gel. Qualitative analyses of the methyl esters were performed with a gas-liquid chromatograph (GLC) equipped with a hydrogen flame ionization detector using a 0.3 x 170 cm glasscolumn packed with 5% SP-2340, 75% cyanopropyl (Supelco, Bellefone, PA) on gasChrom Q, 80-100 mesh (Applied Science Lab, State College, PA). Injections were made at 14O’C with temperature increase of 15”C/min with helium (20 ml/min) used as the carrier gas. Identification of the different peaks was done by comparing their retention time with those of authentic standards and peak areas were integrated by a computing integrator. The gas chromatograph was attached to a Perkin-Elmer- Hitachi RMU6D mass spectrometer with a Biemann separator inter- phase and the esters were identified by comparison of mass spectra of individual components recorded with 70 ev ionizing voltage with those of known standards and on the basis of parent ion and GLC retention time. Spectra were recorded at the ascendingand descend- ing slopes of the chromatographic peak in addition to the top of the peak. Storage experiment To test for the level of oxidative rancidity upon storage of the oil under different conditions of light and temperature, samples of the oil were put in 50 ml tightly capped vials and were divided into two groups. The fnst group consisted of two batches that were stored under indoor natural lighting conditions at 25°C and 32°C. The second group consisted of three batches of sampleswhich were all wrapped in aluminum foil and stored at 7°C (refrigeration tem- perature), 25°C and 32°C and thus were considered to be stored under dark conditions. Samples from the different batches of each group were analyzed periodically for their peroxide values at zero time and at one month intervals for a period of six months according to AOAC (1980). Animal experiment Feeding trials for the detection of any toxicity in the oil were done on one day-old chicks. The semi-purified diets shown in Table 1 and patterned after Scott et al. (1976) were used in the feeding experiment. C. colocynthis oil was compared to corn oil by feeding