Expression of oil from sesame seeds O.O. AJIBOLA, O.K. OWOLARAFE, O.O. FASINA and K.A. ADEEKO Department of Agricultural Engineering, Obafemi Awolowo University, lle-lfe, Nigeria. Received 15 December 1989; accepted 28 July 1992. Ajibola, O.O., Owolarafe, O.K., Fasina, O.O. and Adeeko, K.A. 1993. Expression of oil from sesame seeds. Can. Agric. Eng. 35:083-088. Investigation was carried out on the effects of heating temperature (40 to 85°C), heating time (5.0 to 27.5 min), moisture content (6.1 to 12.0%) and applied pressure (15 and 20 MPa) on the yield, color, refractive index, and specific gravity of oil expressed from sesame seeds using a laboratory press. The yield of oil was affected but the color, specific gravity and refractive index were not affected by processingconditions within the range considered. The oil yieldwas increased withdecreasein moisture contentof sample after heating. Highest oil yield (based on total mass expressed) of 33.5% corresponding to an expression efficiency (based on seed oil content) of 65.7% was obtained when sesame seeds were condi tioned to moisture content of 6.1%, heated at 85°C for 20 min, and expressed at a pressure of 20 MPa. The average values of refractive index andspecific gravity were1.47and0.918respectively while the color of the oil was yellow (i.e. a Munsell color notationof 2.5Y). Ont ete etudies les effets de la temperature de chauffage (de 40 a 85°C),de la duree de chauffage(de 5,0 a 27,5 min), du pourcentage de matiere humide (de 6,1 a 12%) et la pression appliquee (15 et 20 MPa) sur le rendement, la couleur, l'indice de refraction et la densite de Thuile extraite des graines de sesame par le moyen 'un pressoir de laboratoire. Le rendement etait influence mais la couleur, la densite et l'indice de refraction n'ont subi aucune influence due aux conditions de traitement avec les differentes variations prises en compte. Le rendement etait plus grand quand ily avait une reduction de la matiere humide dans les echantillons apres chauffage. La plus grande quantite d'huile (compte tenu de la totalite obtenue) etant 33,5% et correspondant a une efficacite d'extraction de 65,7% (par rapport au pourcentage d'huile dans les graines) a eteobtenue quand les graines de sesame etaient conditionnees a 6,1% de matiere hu mide, chauffees a 85°C pendant 20 min et subies a une pression de 20 MPa au moment d'extraction. Les valeurs moyennes pour l'indice de refraction et la densite etaient respectivement 1,46 et 0,918. La couleur de l'huile etaitjaune(i.e.une notation de couleurMunsell de 2,5Y). INTRODUCTION Sesame seed (Sesamum indicum) is one of the oilseeds that has not been commercially exploited in the world despite its high oil content of about 47% (UNIDO 1977). Sesame seed is consumable, has laxative properties and can be processed into biscuit. The oil obtained from sesame seed is golden yellow in color and requires little or no refining. The oil can be used in salad dressings, and the manufacture of cosmetics such as soap, hair conditioners, and bath oil. The cake ob tained after expression can be used in the preparation of livestock feed. The mechanical expression of oil from oilseeds is the most common method used for the removal of oil from oil-bearing materials. This method is economical for small and medium scale oil processors in the developing countries (Singh et al. 1984). Although the use of a hydraulic press during expres sion results in lower oil removal efficiency, it is preferred to the screw press by small scale producers because of lower initial and running costs. The amount of oil expressed using the hydraulic press is affected by the pre-pressing and press ing conditions such as particle size, moisture content, heating temperature, heating time, applied pressure, and pressing time (Khan and Hanna 1983). Steinbock (1948) explained, that with the exception of very small sized seeds like sesame, reduction of oilseeds to flakes by rolling is essential with the size and hardness of the seeds determining the number of stages for the flaking operation. Heating is essential because it completes the breakingdown of oil cell walls, lowers the viscosity of the oil to be expelled, coagulates the protein in the meal, and adjusts the moisture content of the meal to the optimum level for pressing (Ward 1976). Oil yield has been shown by several researchers to be affectedby the tempera ture and duration of heating (Ajibola et al. 1990; Fasina and Ajibola 1989; Sivakumaran et al. 1985; Singh et al. 1984). High heating temperatures and long heating times may have negative effects on the quality of expressed oil and cake residue (Anjou 1972;Ohlson 1976). It is therefore important to identify the optimal heat treatment required for processing sesame seed. The moisture content of oilseeds before pressing affects the yield and quality of oil expressed. Cloudy oilis obtained from seeds with high moisture content. Therefore, moisture content adjustment of the seeds is necessary before pressing. Vaughan (1970) explained that the effectof moisture content on expression efficiency canbe related to mucilage develop ment in the outer epidermal cells of the seeds. The mucilage coating can impede the flow of oil from the cotyledon tissue. High oil yields ranging between 37.0 and 39.6% were ob tained from samples of conophor nut with post-heating moisture content between 8 and 10% (dry basis) (Fasina and Ajibola 1989), while maximum oil yields of about 40% were obtained when the moisture contents of melon seed samples were reduced by about 5% (dry basis) (Ajibolaet al. 1990). Singh et al. (1984) observed that the moisture content of sunflower seed was the most significant factor affecting the expression of oil from the seed. Pominski et al. (1970) reported that the optimum pressure for maximum oil yield may be dependent on the pre-pressing operation and the type of seed being expressed. They found that the amountof oil expressed from peanuts tended to level off at expression pressure of 15 MPa and above, while Adeeko and Ajibola (1990) found a pressure of 20 MPa as optimum pressure for the expression of oil from groundnut. The oil yield from conophor nut was found to increase with increase in applied pressurefrom 10 MPa to 25 MPa (Fasina CANADIAN AGRICULTURAL ENGINEERING Vol. 35, No. 1, January/February/March 1993 83