Microwave-Assisted Extraction of Soybean and Rice Bran Oil: Yield and Extraction Kinetics

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Microwave-assisted solvent extraction has the potential to replace traditional solvent extraction of oils and fats from a variety of feedstock. The purpose of this study was to optimize oil extraction parameters for a batch microwave system from two feedstocks: soybeans and rice bran. Solvent-feedstock mixtures were exposed to microwave radiation for different time-temperature combinations ranging from 60C to 120C for up to 20 min with simultaneous magnetic stirring. The solvent (ethanol) to feedstock ratio used was 3:1. After extraction, solid-liquid separation was performed in a vacuum filter, and ethanol was evaporated from the filtrate in a vacuum centrifuge. Results showed that the oil yield changed with temperature and achieved a maximum value in a relatively short time (order of minutes). Continuous exposure after this time did not increase the oil yield. The results compared well with traditional solvent extraction, especially when accounting for the extremely short extraction times (min vs. h). Maximum oil yields of 17.3% and 17.2% at 20 min and 120C were achieved by microwave extraction as compared to 11.3% and 12.4% using control extraction for soybeans and rice bran, respectively. The major advantage of microwave-assisted solvent extraction is the reduced time of extraction required to obtain ~95% of total recoverable oil, with corresponding reduction in energy consumption costs per unit of oil extracted.