Congratulations to our new doctor Minale Ouethrani's who graduated with the very honourable grade !

Her thesis defense took place on March 25th 2011 in Agroparistech Centre de Paris Claude Bernard,

Thesis :
Chemical contaminants in coffee: developpement of analytical methods and investigation of their bioavailability

Abstract :
Coffee brew is one of the most frequent drinks consumed in the world, but its health effects
are still in debate as it remains a heterogeneous complex matrix. Even though some of its
major constituents have a beneficial health effect (i.e polyphenols), toxic organic
contaminants are also present such as OTA, PAHs or acrylamide. The role of the gut
microbiota in the metabolism of such contaminants has been often overlooked and is a crucial
step in risk assessment. After the development of a straightforward analytical method for the
simultaneous quantification of the targeted compounds using a semi-automated solid-phase
extraction procedure with HPLC-FLD analysis, we used in vitro methodologies to study the
metabolism of coffee contaminants by the human gut microbiota. Batch cultures as well as
SHIME experiments showed that the human gut microbiota is able to degrade OTA with
formation of OTα and OTB (newly microbial metabolite identified in vitro) which can be
considered as a detoxification pathway. Using the SHIME, we have also investigated the
effects of OTA and its association with coffee brew on the human gut microbiota by
monitoring the fermentation activity and the composition of the microbiota by TTGE and
DGGE. Major fermentation shifts were observed during the coffee + OTA period throughout
a more important production of SCFAs and a paralleled decrease in ammonium. While no
major change was observed within the dominant bacterial populations, notable changes could
be observed towards Lactobacillus and Bifidobacterium species. In particular, L. reuteri was
found to be greatly reduced by OTA. Further research is needed to study the possible
consequences on the host physiology.