Optimization of the extraction of triterpenes from Ganoderma lucidum

Ganoderma lucidum is a mycological source rich in several bioactive compounds. Among their constituents, triterpenes have been widely reported to be responsible for some of G. lucidum bioactive properties [1]. It has been used, since ancestral times, due to their medicinal and nutraceutical properties. In this context, the achievement of extracts enriched in target compounds, and obtained at optimized extraction conditions, is a relevant field of research where the use of statistical tools, such as response surface methodology (RSM), is becoming increasingly important. In the present study, the extraction of triterpenes from G. lucidum was optimized by using maceration (ME) and ultrasound assisted extraction (UAE), and compared with Soxhlet extraction (SE). The SE technique was considered effective by applying 7 cycles while to optimize ME and UAE, RSM was applied using a circumscribed central composite design with three independent variables (time, ethanol content, temperature (ME) or power (UAE)). The extraction yield and content in triterpenes were maximized and the extracts obtained under the optimal conditions characterized in terms of individual triterpenoids by HPLC-DAD-ESI/MS analysis. With the SE technique, a positive linear dependency was achieved for the extraction yield while an asymptotic-decreasing behavior was observed for triterpenes’ content. The conditions maximizing responses were: 78.9 min, 90ºC and 62.5% ethanol and 40 min, 100 W and 89.5 % ethanol for ME and UAE, respectively. The later was the most effective, yielding 4.9±0.6% and 435.6±21.1 mg equiv. ursolic acid/g extract whereas the first yielded 5.2±0.6% and 285.7±31.2 mg equiv. ursolic acid/g extract. Under the optimum conditions, HPLC-DAD-ESI/MSn analysis confirmed the presence of a total of 24, 26 and 28 triterpenes in the extracts obtained by ME, UAE and SE, respectively. These results show the potential of G. lucidum as a source of bioactive compounds pointing out for their use in several industrial applications.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 (POCI-COMPETE2020) for financial support to CIMO (UID/AGR/00690/2013) and LA LSRE-LCM (POCI-01-0145-FEDER-006984). Project NORTE-01-0145-FEDER-000006, funded by NORTE2020 under the PT2020, through FEDER.