Green and solvent-free simultaneous ultrasonic-microwave assisted extraction of essential oil from white and black peppers

Essential oils were extracted from white and black peppers (Piper nigrum L.) by green and solvent-free ultrasonic-microwave assisted extraction (UMAE), microwave assisted extraction (MAE) and ultrasonic assisted extraction (UAE), and the efficiency and free radical scavenging activities of the essential oils by different extraction methods were compared in order to illuminate their advantages and disadvantages. The oil yield and superoxide radical scavenging activity of white pepper by UMAE were both significantly higher than those oil extracted by MAE and UAE, implying that UMAE was far more efficient extracting method than MAE and UAE. The same trends were also found for black pepper. Meanwhile, the bioactive compounds of the essential oils from white and black peppers were also characterized and compared by GC coupled with mass spectrometry (GC-MS) and electronic nose based on fast gas chromatography (GC). The essential oil from black pepper contained more monoterpenes than the oil from white pepper, while white pepper oil showed higher content of sesquiterpenes than black pepper. For the different extraction methods, generally, UMAE could obtain more monoterpenes and sesquiterpenes than MAE and UAE. UMAE should be an emerging effective green extraction technique for essential oil from P. nigrum because of the maximum extraction yields, shortest extraction time and solvent-free. The electronic nose has been proven as a useful tool for quick analysis and discrimination of the essential oils by different extraction methods.