Semi-automated solid-phase extraction method for studying the biodegradation of ochratoxin A by human intestinal microbiota

A simple and rapid semi-automated solid-phase (SPE) extraction method has been developed for the analysis of ochratoxin A in aqueous matrices related to biodegradation experiments (namely digestive contents and faecal excreta), with a view of using this method to follow OTA biodegradation by human intestinal microbiota. Influence of extraction parameters that could affect semi-automated SPE efficiency was studied, using C18-silica as the sorbent and water as the simplest matrix, being further applied to the matrices of interest. Conditions finally retained were as follows: 5-mL aqueous samples (pH 3) containing an organic modifier (20% ACN) were applied on 100-mg cartridges. After drying (9 mL of air), the cartridge was rinsed with 5-mL H2O/ACN (80:20, v/v), before eluting the compounds with 3× 1 mL of MeOH/THF (10:90, v/v). Acceptable recoveries and limits of quantification could be obtained considering the complexity of the investigated matrices and the low volumes sampled; this method was also suitable for the analysis of ochratoxin B in faecal extracts. Applicability of the method is illustrated by preliminary results of ochratoxin A biodegradation studies by human intestinal microbiota under simple in vitro conditions. Interestingly, partial degradation of ochratoxin A was observed, with efficiencies ranging from 14% to 47% after 72 h incubation. In addition, three phase I metabolites could be identified using high resolution mass spectrometry, namely ochratoxin α, open ochratoxin A and ochratoxin B.