Performance Evaluation of a Screw Type Oil Expeller for Extraction of Sesame Oil

Sesame, (Sesamum indicum) is one of the oldest and important oil seed crop in the world. The sesame seed apart from providing edible oil is also rich in protein. A study was carried out to evaluate the performance of a medium scale screw type oil expeller for extracting sesame oil. In fact, the mechanized medium scale method has not been previously applied in the oil expelling industry for sesame seed in Sri Lanka. For this experiment, the popular screw type machine with 25 mm shaft pitch, 75x315 mm internal barrel and 4 kW three phase motor were used. The development was made in order to increase the oil expelling efficiency in terms of extract bar clearance, speed of the main spiral shaft and outer body closer to the exhaust out let. The optimum oil yield was 44% obtained under 0.2mm and 0.3mm barrel shaft clearance and the main spiral shaft speed of 75 rpm. The quality of refined oil at maximum oil yield was analysed out in terms of saponification value, free fatty acid and specific gravity. The results obtained for saponification value, free fatty acid and specific gravity were 182.33, 3.3.12 % and 0.917 gcm-3.respectively. Color of the sesame oil was closer to the yellow which revealed by the lightness value (L*) of 26 and positive value b of 8.27. The capacity and energy consumption per kilograms of refined sesame oil were 39kg/hr and 0.103kWh/kg. This study reveals that sesame oil could be obtained using the screw type oil expeller and it can be recommended for medium scale entrepreneurs relative to the traditional Sekku method.


Introduction
The sesame is one of the world most important and oldest known oil seed crop (Abou-Gharbia et al., 1997).The sesame crop is adapted and cultivated both in the tropic and temperate zones of the world (Biabani and Pakniyat, 2008).It is grown mostly for the oil extracted from the seed which is edible and use for industrial and pharmaceutical purposes.The oil is used in the production of perfumes, skin conditioning agents, moisturizers, hair creams, bath oil, insecticides, paints, vanishes and drugs (Mohammed and Hamza, 2008).
Sesame Seed (Sesamum indicum) Oil has also been used as medicinal oil for thousands of years.Sesame oil is mentioned in the Vedas as excellent for humans.It is naturally antibacterial for common skin pathogens, such as staphylococcus and streptococcus as well as common skin fungi, such as athlete's foot fungus.It is naturally antiviral.It is a natural anti inflammatory agent.(http://www.youthingstrategies.com) Therefore, sesame has been named as a national high priority crop in Sri Lanka.But sesame oil is very expensive and not freely available for consumers whenever, they need.The main constrain for this is unavailability of oil processing machinery and equipments in the market.
The world harvested about 3.84 million metric tons of sesame seeds in 2010.The world's largest exporter of sesame seeds was India, andJapan is the largest importer.According to the Export Development Board records Sri Lanka also exports sesame and its annual production as per the records in 2009 of Department of Census and Statistics, Sri Lanka is around 8750 MT.The extraction of sesame oil from the sesame seed is not a completely automated process in Sri Lanka.Even at the present, it is done by using the traditional method called "Sekku" method.However, in some instance, screw type coconut extractors are being used for extraction of sesame oil.But, above methods have not been previously evaluated for their performance.Most of the time, people in different sectors request a perfect medium scale method for sesame oil extraction.Hence, this study aims at evaluating the most common type of extractor available in the market in sesame oil extraction with a view to improving its performance Expeller pressing (also called oil pressing) is a mechanical method for extracting oil from raw materials.The raw materials are squeezed under high pressure in a single step.When used for the extraction of food oils, typical raw materials are nuts, seeds and algae, which are supplied to the press in a continuous feed.As the raw material is pressed, friction causes it to heat up; in the case of harder nuts (which require higher pressures) the material can exceed temperatures of 120 °F (Wikipedia).

Eng. (Mrs
An expeller press is a screw-type machine that presses oil seeds through a caged barrel-like cavity.Raw materials enter one side of the press and waste products exit the other side.The machine uses friction and continuous pressure from the screw drives to move and compress the seed material.The oil seeps through small openings that do not the pressed seeds are formed into a hardened cake, which is removed from the machine.Pressure involved in expeller pressing creates heat in the range of 140-210 °F (60-99 °C) (Wikipedia).

Methodology
For this experiment, the popular Chinese origin screw type oil expeller machine with 25 mm pitch of screw shaft, 75x315 mm internal barrel and 4 kW three phase motor were used.The machine mainly consists of pressing part, adjustment part and transmission part.This machine, common in coconut oil extraction was used to modify for sesame oil extraction in custom level.The screw assembly is formed integrally with this shaft.This screw rotates within a cage or barrel.The barrel is made of case hardened, tool steel bars.The clearance spaces are used between the lining bars or rings to allow drainage of the oil as the pressure on the feed material is increased.At the discharge end, a movable choke or cone controls the operating pressure (Ajao, K.R atel, 2009).
The inbuilt belt transmission was consisted with 6" diameter drive pulley and 12" diameter driven pulley.The rotational speed was set up for four different speeds by varying drive pulley diameter 2.5", 3", 4" extras and the inbuilt pulley of 6".
As the drive shaft diameter is one inch, the smallest pulley diameter compatible with the drive shaft could only be 2.5 inches.Table : 1 shows how the speed varied using different drive pulleys and their speed ratios.The sample obtained from "Sekku" traditional method was taken for analysis.
A homogeneous bulk sample of sesame seed, belonging to the popular Sri Lankan variety MI-2, was used for the experiment.Oil yields from the samples were recorded as percentage of raw material fed as stated below.Percentage of free fatty acid (ffa) in each sample of sesame oil was calculated according to the AOCS method using equation (6).

W = Weight of oil sample (g)
The color of the oil samples was determined using a Chroma meter (Konica Minolta, Model CR-400).Representative oil samples were introduced to the Chroma meter and readings of L*a*b values were taken.Data gathered were analyzed using Analysis of (Annon, 2000) screw type oil expeller normally uses for coconut oil extraction.The extract bar clearance that was originally 0.1 mm, which was adjusted to 0.2 mm on one side and 0.3 mm other side.Another problem was the pressure releasing outlet on the cylindrical body.Before performing the cake, the mixer comming through this whole was mixed with the extracting oil.This was a problem to the was made to direct the pressed mixer to the cake speed ratios of the machine, the oil expelling trials were conducted as per the speed stated in Table 1.To evaluate the machinery performance, crude oil yield, machine capacity and energy consumption at different speed of screw shaft were calculated.
(2000) who reported a high content of oil for the dehulled sesame seeds (58.9%).According to the Table 2, there is no oil extraction happened at the speed of 180 rpm.And it shows the crude oil yield has been increased when the speed of the screw shaft decreased.The maximum oil yield, of 44% was obtained at the speed of 75 rpm.This speed is the lowest level of speed that only could be achieved between each and every speed level.Beyond this level, pulley diameter of this selected machine couldn't be reduced.To get the speed lower than that, it is needed to change the driven pulley also.
There will be a more extra work for users.The achieved at the speed of 75 rpm and it is the most the lowest speed.Considering the percentage of oil yield, Machine Capacity and Energy consumption during expelling, the best performance is given the speed of 75 rpm which could be achieved by the machine without modifying.An oil-rich seed such as sesame seed or groundnut yields about 5 percent less oil in a traditional than in a mechanical The chemical properties of oil are amongst the most important properties that determines the present condition of the oil.Free fatty acid and peroxide values are valuable measures of oil the 75 rpm speed of the machine and the Sekku that were recorded for the machine speed of 75 rpm and Sekku method are 182.33 and 182.02 respectively.According to the SLSI standards the 188-193.
Though the Free Fatty Acid value of sesame oil according to the SLSI standards is 2.5%, all the samples in Table 2 exceed the 3.12%.While of the 75 rpm speed of the machine and the Sekku method.
According to the Hunter lab L*,a, b colour spaces, the lightness index of the sample.Table 2 shows all the samples are comply with positive b values shows that when the machine speed decreases the lightness of the colour increases.There is no 75 rpm and Sekku method.
In overall, Table 2 noticeably shows that all the of the Sekku traditional method.From this research survey, it was found that Sekku traditional method is the most popular method for usage of sesame oil for traditional Ayurvedic treatments.The screw type oil expeller which is commonly used in Sri Lanka for extraction of coconut oil in medium and small scale can be economically used for extracting sesame oil.The optimum process parameters for expression of highest yield of crude obtained under 0.2mm and 0.3mm barrel shaft clearance and the main spiral shaft speed of 75 rpm Sincere thanks are due to Seedevi Importers (Pvt) research project.Authors also like to acknowledge the services of other members of the Institute of Post Harvest Technology (IPHT) for their fullest corporation extended in this regard.

Figure 1 -
Figure 1 -Sectional view of the screw type oil expeller of the sesame fed (kg) T = Time taken for processing (hr) The energy consumption of extraction per kilogram of oil was calculated by considering power consumed by the oil expeller.Where, P = Electrical power consumed (kW) O = Crude oil recovered (kg) Oil weighed and measured the volume then mentioned below.Where, Ww = Sample weight (g) Sv = Sample volume (cm3) molecular weight of a fat or oil.According to the Where, B -ml of HCl required by Blank.S -ml of HCl required by Sample.