Abstract: Ultrasound at 100 kHz was used to enhance the extraction of polyphenolic compounds from Satsuma mandarin peel by the conventional soaking method. It was found that the addition of ultrasound assistance during the soaking of Satsuma mandarin peel in 80% methanol aqueous solution allowed more effective and efficient extraction of phenolic acids at low temperature. The effects of ultrasound treatment time, extraction temperature and ultrasound power on phenolic acid content and antioxidant capacity of extracts were studied and the results indicated that extraction temperature had the most important effect. A considerable increase of phenolic acid content in Satsuma mandarin peel extracts was observed with increasing temperature, while prolonged ultrasound treatment time resulted in a significant reduction of phenolic acid content at 40 ℃. Moreover, an excellent linear relationship between total phenolic content and antioxidant capacity of Satsuma mandarin peel extracts was found, revealing a R2 of 0.8435, 0.8895, 0.8622 at 15, 30 ℃ and 40 ℃ and of 0.7971 at various ultrasound power levels, respectively. Accordingly, Satsuma mandarin peel is an abundant source of antixodiants. This study also demonstrates that ultrasound assistance can effectively increase phenolic acid content and antioxidant capacity of Satsuma mandarin peel extracts.

Key words: ultrasound-assisted extraction, Satsuma mandarin peel, polyphenol, antioxidant capacity, relationship