Alternative extraction strategies for biosurfactants produced by solid-state fermentation from organic waste

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This study investigates alternative extraction techniques in solid-state fermentation of organic substrates. Extracting from a solid matrix is a significant downstream processing challenge, as most technologies are adapted from those used in submerged fermentation without accounting for the solid matrix's intrinsic properties. In this study, extraction of sophorolipids (SL) through conventional ethyl acetate solvent extraction (maceration) was compared to pressurized liquid extraction (PLE) and ultrasound-assisted extraction (UAE). SL are especially relevant not only as potential substitutes to some traditional surfactants but also because of their interesting antimicrobial and anti-cancer properties. All strategies used both ethyl acetate and ethanol to reveal the effect of the solvent on the processes. In this study, PLE with ethyl acetate achieved the highest crude SL yields (0.443 g crude SL/g dry fermented solid). UAE yielded results similar to traditional extraction but reduced the time from 2 h to 30 min; while ethyl acetate generally resulted in higher total crude extracts, ethanol improved SL extraction across all methods. PLE using ethanol achieved the highest SL yields with high purity (0.063 g final extract/g dry fermented solid and 62 % SL content). Afterwards, supercritical fluid extraction with CO 2 (SFE-CO 2 ) was employed to selectively remove fatty acids and oils from the fermented solids as a pretreatment step before SL extraction. This improved SL recovery, and by performing a sequential ethanol PLE after SFE-CO 2 in the same cell, a 308 % increase in extracted SL yield was achieved compared to traditional solvent extraction with ethyl acetate. This approach also showed itself to be the greenest one following the Path2green methodology and considering solvent consumption. This research shows that PLE, SFE, and UAE are promising, more sustainable, and efficient alternatives to traditional solvent extraction.

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