Effect of microwave pre-treatment on the yield of soybean oil extraction process: kinetic study, mathematical modeling and optimization

Abstract

Soybean is one of the main oilseeds cultivated in Brazil. Solvent extraction is an essential operation in soybean industrialization. New technologies have been developed to increase the efficiency of extraction, highlighting microwave-assisted extraction. In this context, this work aimed to study the effect of microwave pretreatment on the soybean oil extraction yield by hexane, investigate the kinetic mechanism of extraction and optimize the process. Previously characterized soybeans were submitted to microwave pretreatment varying the applied nominal power (310 and 620 W) and the pretreatment time (5, 10, 20, and 30 s), followed by 30 minutes in the conventional extraction. The oil extraction yield and the extract concentration were evaluated in each treatment. A polynomial equation was developed to model these variables. The response surface optimization method was applied to the model to maximize the extraction yield. Furthermore, two kinetic models (first order and second order) were fitted to the experimental data, to investigate the kinetic mechanism of microwave pretreatment. The results obtained showed that the pretreatment time and the applied nominal power had significant effects on the extraction yield, which was predicted with 81% accuracy by the proposed model. In the optimization study, the model indicated that the maximum yield achieved in the microwave-assisted extraction process would be about 10%, for the operational settings of 30 s and 620 W. In addition, the kinetic study revealed that the soybean pretreatment was satisfactorily described by both the first-order model and the second-order model. In summary, the microwave pretreatment showed to be promising for the conventional soybean oil extraction process, since the processing time was reduced from 240 min to 60 min.