Megasonic-assisted aqueous extraction of canola oil from canola cake

Residual oil in post-expeller canola cake, is industrially recovered by solvent extraction using hexane with greater than 90% recovery. However, due to health and environmental risks, industry is seeking safer and air polluting alternatives to hexane. The present work explores the application of ultrasound in the megasonic range for aqueous-based extraction of oil from canola cake. A factorial experiment was designed to examine various ultrasound and canola cake extraction parameters including frequency (0.4, 1, and 2 MHz; 33.6–122.4 kJ/kg), sonication time (10, 20, and 30 min), cake: water ratio (1:9, 2:8 and 3:7 w/w), and temperature (60, 70, and 80 °C). A rapid and simple aqueous-based megasonic extraction method was established for preliminary screening of studying the effect of processing parameters for maximising oil extractability. We also assessed the oil quality tests for each condition by analysis of free fatty acids (FFA), peroxide value (PV), and chlorophyll for the best conditions. Control (non-megasonic) trials were also carried out in parallel to determine the net ultrasound extractability (NUE). The highest NUE obtained was 49.5% (g oil/100 g hexane extractable oil in meal) at treatment conditions of 2 MHz, 30 min, meal: water 1:9 (w/w), and 80 °C. An aqueous-based centrifugation method was then established and tested under the same conditions without and with ultrasound, giving a net ultrasound yield improvement (NUY) of 31.8% (g oil/100 g meal) and a NUE of 30.6%. The canola oil quality after ultrasound aqueous-based extraction met the industry standard specifications for free fatty acids, chlorophyll, peroxide, and phosphorus content.