Combining integrated ultrasonic-microwave technique with ethanol to maximise extraction of green coffee oil from Arabica coffee beans

This study was designed to integrate ultrasonic-microwave assisted extraction (UMAE) with ethanol, a green solvent, to extract green coffee oil (GCO) from green coffee beans. Response surface methodology was utilised to maximise the efficiency of GCO extraction. Structural changes occurring in the coffee residue were explored using scanning electron microscopy, and extraction kinetics was established. Results indicated that the yield of GCO obtained by UMAE under optimum conditions (microwave power 350 W; extraction time 10 min; and liquid-solid ratio 28:1 mL/g) was 10.58 +/- 0.34%. Extraction kinetics revealed that UMAE exhibited higher efficiency and took less time (10 min vs 5 h with solvent extraction) compared with conventional process. The highest contents of kahweol and cafestol found in the UMAE extract were 12.00 and 22.28 mg/g oil, respectively. This study demonstrated that UMAE with ethanol is a rapid, efficient, and environmentally friendly green technique for the extraction of green coffee oil.