Degradation of steviol glycosides via steviol and Monicanone by soil microorganisms and UASB effluent.

Steviol glycosides are fully deglycosylated to steviol in the presence of bacterial populations that were isolated from different soil samples. Heating (20 min at 80 °C) or boiling (10 min at 100 °C) of soils had little effect on the steviol formation. It is suggested that bacteria that survived with highly resistant spores are responsible for the deglycosylation of steviol glycosides. A bio-organic preparation method for steviol was developed which had a total yield of 90%. Beside deglycosylation, other reactions also occur. The steviol formed can be degraded. Under anaerobic conditions, rebaudioside A was not hydrolyzed while stevioside was degraded to steviol via rubusoside. Moreover, after an extended incubation (4 weeks) and repetitive sub-cultivation, a bacterial community was selected that converted steviol glycosides to a new and unknown ketone, given the nickname Monicanone. It appeared to be the steviol nucleus without the A-ring that underwent a Walden inversion at its original C-10. A second and related unknown compound could be isolated from an impure preparation of Monicanone by chromatographic separation and purification; this compound was a reduced form of Monicanone and named Monicanol. Steviol glycosides that were incubated with a UASB effluent of an industrial wastewater treatment system – supplemented or not – with sludge of a lab scale nitrification or denitrification unit – were completely degraded via steviol and Monicanone. [Display omitted] • Steviol glycosides (SG) were initially hydrolyzed to steviol by soil samples. • Steviol was fully degraded by extension of the incubation period. • In anaerobic conditions, the deglycosylation pathway was different. • SG were converted to Monicanone by a specific bacterial consortium. • SG were fully degraded via steviol and Monicanone by a sample of an UASB effluent. [ABSTRACT FROM AUTHOR]