Optimization of oil extraction from sunflower seeds using the microwave- ultrasound pretreatment

The sunflower (Helianthus annuusis) an annual verb from Astraceae genus that is grown as a firm bush. One of the oil extraction methods is the mechanical extraction (press) that is usually used in small scales. The main limitation of oil extraction using press is the high amount of residual oil in the meal. Therefore, recently some techniques, such as oil extraction using ultrasound and microwave, are taken into consideration in this case. The ultrasonic waves are some types of mechanical waves that have frequencies are higher than human hearing and microwaves are the non-ionized electromagnetic waves with frequencies range between 300 MH to 300 GH, and are placed between the radio and infrared ray in the electromagnetic spectrum. Regarding the fact that no research is performed in the case of applying the sequential pretreatment of extracting oil from sunflower seeds, for this reason in the current research it was tried to study the utilization of microwave-ultrasound pretreatment in extracting oil from sunflower seeds.

In performing this research the sunflower seeds (contain 38.5 percent oil) was prepared from Agricultural and Natural Resources Research Centre of Golestan Province. Then external materials such as weed seeds, sand and stones were separated by hand and transferred to the Food Industry laboratory of Azad Islamic University of Gonbad-e-Kavoos to perform experiments. At first the seeds were processed by microwave pretreatment with power of 540 watt and different times of process(0 to 120 seconds) and after this they were treated by an ultrasonic bath device with three different time levels(0 to 50 minutes) with stable frequency of 35 KH. After applying these treatments, the oil of seeds were extracted using the screw press with different speeds (11 to 57 rpm) and some experiments such as the efficiency amount of oil extraction, refractive index, color index, acidity and total phenolic compounds were performed on these oils. The response surface methodology, using the Box-Behnken design, was used to evaluate the constant parameters of study in comparison to the variable parameters.

Increase in the microwave and ultrasound time increased the oil extraction efficiency; although in the high ultrasound or microwave times with increase in these two parameters the amount of oil extraction efficiency decreased because of oil outlet ducts destruction. Increase in the oil extraction efficiency with increase in the microwave time can be related to more fracture of oil contained cells or is resulted from decomposition or destruction of protein compounds during treatment with microwave, on the one hand with increase in the ultrasound time some cavitations bubbles are created which have high collapse and explosion power and the force generated from bubbles explosion will lead to an increase in the cell membrane destruction. With increase in the rotational speed of press, the amount of extraction efficiency decreased a little because of reduction in the amount of pressure applied on seeds. The lowest amount of oil acidity that was measured on the basis of Oleic Acid was obtained in the conditions that no pretreatment was used in oil extraction and the rotational speed of screw press was 34 rpm. With increase in the microwave and ultrasound time, the amount of oils color index will increase. Also with increase in the rotational speed of press, the amount of color index increased too. The reason of increase in the amount of color index with increase in the microwave and ultrasound time and also with the rotational speed of press can be attributed to more release of chromogenic compounds in the extracted oil. All of the experiment variables (microwave and ultrasound time and rotational speed of screw press) didn’t have any influence on the refractive index of oils and its amount were equal to 1.0471 for all of the measured and evaluated samples. With increase in the microwave and ultrasound time, the total phenol of oils was increased at first and decreased then. Also optimization of this process indicated that if the microwave time is 33.71 seconds, the ultrasound time is 28.38 minutes and the rotational speed of screw press is 11 rpm, they will lead to obtain the regarded aims. At last it can be said that applying the microwave-ultrasound pretreatment can be propounded as an appropriate pretreatment in the oil extraction industry. With increase in the microwave and ultrasound time, the total phenol of oils was increased at first and decreased then. Also optimization of this process indicated that if the microwave time is 33.71 seconds, the ultrasound time is 28.38 minutes and the rotational speed of screw press is 11 rpm, they will lead to obtain the regarded aims. At last it can be said that applying the microwave-ultrasound pretreatment can be propounded as an appropriate pretreatment in the oil extraction industry. With increase in the microwave and ultrasound time, the total phenol of oils was increased at first and decreased then. Also optimization of this process indicated that if the microwave time is 33.71 seconds, the ultrasound time is 28.38 minutes and the rotational speed of screw press is 11 rpm, they will lead to obtain the regarded aims. At last it can be said that applying the microwave-ultrasound pretreatment can be propounded as an appropriate pretreatment in the oil extraction industry.With increase in the microwave and ultrasound time, the total phenol of oils was increased at first and decreased then. Also optimization of this process indicated that if the microwave time is 33.71 seconds, the ultrasound time is 28.38 minutes and the rotational speed of screw press is 11 rpm, they will lead to obtain the regarded aims. At last it can be said that applying the microwave-ultrasound pretreatment can be propounded as an appropriate pretreatment in the oil extraction industry.