Effect of enzymatic and hydrothermal treatments of rapeseeds on quality of the pressed rapeseed oils: part II. Oil yield and oxidative stability

Response surface methodology was used to evaluate the quantitative effects of three independent variables: rapeseed moisture content (MC), enzymes dosage (ED) and conditioning temperature (T) on rapeseed oil yield (OY), efficiency of pressing (EP), and oxidative stability (OS). The highest OY (16.4%) and EP (42.8%) were obtained from pectolytic enzyme (0.1%) treated seeds (MC = 9%, T = 90 °C). The highest OS (12.6 h) was found for oil pressed from rapeseeds heated at 120 °C (MC = 11%), after the cellulolytic enzyme treatment. Results of OY, EP and OS determinations correlate with the predicted values calculated from the partial cubic models (PCMs) equations (R2 = 0.9995, 0.9994, 0.9974 for the cellulolytic enzyme-treated oils and 0.9900, 0.9900, 0.9990 for the pectolytic enzyme-treated oils). The predicted optimum MC = 9.5% and 8.6%, ED = 0.06% and 0.1%, T = 91.2 °C and 90.1 °C resulted in OY = 15.5% and 16.5%, EP = 40.4% and 43.0% for rapeseed oils from seeds treated with cellulolytic and pectolytic enzymes. OS values (12.6 h and 11.8 h) at the optimum conditions of MC = 11.0% and 10.1%, ED = 0.04% and 0.08%, T = 120.0 °C and 119.9 °C for the cellulolytic and pectolytic enzyme-treated oils were also calculated using PCM. Moreover, scanning electron microscopy revealed structural changes in the rapeseed after enzymatic treatment.