Optimization of ultrasound-assisted extraction of oil from olive pomace using response surface technology: Oil recovery, unsaponifiable matter, total phenol content and antioxidant activity

•Ultrasound-assisted extraction (UAE) was used for olive pomace oil recovery.•Unsaponifiable matter, total phenol content and antioxidant activity were studied.•Response surface methodology (RSM) was used for modelling and optimization.•Experimental values obtained were compared against conventional Soxhlet extraction.•The UAE proved to be more adequate for valorisation of solid olive by-product.

The optimum conditions for ultrasound-assisted extraction of olive pomace oil were determined by response surface methodology (RSM). The effect of temperature, solid/liquid ratio and particle size was investigated on oil yield, its unsaponifiable matter (USM%), total phenol content (TPC) and antioxidant activity (DPPH). The optimal condition for the oil yield was: temperature, 60 °C, solid/liquid ratio, 1/12  g/mL and particle size, 0.5 mm. At this condition, the oil recovery was 11.03% which well matches with the predicted value. The optimal point for the USM% was achieved when the UAE is carried out at 55 °C using solid/liquid ratio 1/12 g/mL and particle size 0.5 mm. The optimal conditions for TPC of olive pomace oil obtained and its antioxidant activity were as follows: temperature, 50 °C, solid/liquid ratio, 1/8 g/mL and particle size, 0.9 mm and temperature, 55 °C, solid/liquid ratio, 1/8 g/mL and particle size, 0.9 mm, respectively. Close agreement between experimental and predicted values for USM%, TPC and DPPH was found.