Ultrasound and microwave assisted extraction of ergosterol from Agaricus bisporus L.: Optimization through response surface methodology
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resumo
There is scientific evidence demonstrating the benefits of mushrooms ingestion due to their richness in
bioactive compounds such as mycosterols, in particular ergosterol [I]. Agaricus bisporus L. is the most
consumed mushroom worldwide presenting 90% of ergosterol in its sterol fraction [2]. Thus, it is an
interesting matrix to obtain ergosterol, a molecule with a high commercial value. According to literature,
ergosterol concentration can vary between 3 to 9 mg per g of dried mushroom. Nowadays, traditional
methods such as maceration and Soxhlet extraction are being replaced by emerging methodologies such as
ultrasound (UAE) and microwave assisted extraction (MAE) in order to decrease the used solvent amount,
extraction time and, of course, increasing the extraction yield [2]. In the present work, A. bisporus was
extracted varying several parameters relevant to UAE and MAE: UAE: solvent type (hexane and ethanol),
ultrasound amplitude (50 - 100 %) and sonication time (5 min-15 min); MAE: solvent was fixed as
ethanol, time (0-20 min), temperature (60-210 •c) and solid-liquid ratio (1-20 g!L). Moreover, in order to
decrease the process complexity, the pertinence to apply a saponification step was evaluated. Response
surface methodology was applied to generate mathematical models which allow maximizing and
optimizing the response variables that influence the extraction of ergosterol. Concerning the UAE, ethanol
proved to be the best solvent to achieve higher levels of ergosterol (671.5 ± 0.5 mg/100 g dw, at 75%
amplitude for 15 min), once hexane was only able to extract 152.2 ± 0.2 mg/100 g dw, in the same
conditions. Nevertheless, the hexane extract showed higher purity (11%) when compared with the ethanol
counterpart ( 4% ). Furthermore, in the case of the ethanolic extract, the saponification step increased its
purity to 21%, while for the hexane extract the purity was similar; in fact, hexane presents higher
selectivity for the lipophilic compounds comparatively with ethanol. Regarding the MAE technique, the
results showed that the optimal conditions (19 ± 3 min, 133 ± 12 •c and 1.6 ± 0.5 g!L) allowed higher
ergosterol extraction levels (556 ± 26 mg/100 g dw). The values obtained with MAE are close to the ones
obtained with conventional Soxhlet extraction (676 ± 3 mg/100 g dw) and UAE. Overall, UAE and MAE
proved to he efficient technologies to maximize ergosterol extraction yields.
