The degradation of curcuminoids in a human faecal fermentation model.

In the present study, the colonic metabolism of three curcuminoids (80.1% curcumin, 15.6%, demethoxycurcumin (DMC) and 2.6% bis-demethoxycurcumin (Bis-DMC)) was evaluated using an in vitro model containing human faecal starters. The breakdown products formed were identified and characterized using different analytical platforms. Following in vitro incubation, the relative amounts of degraded curcuminoids and the produced metabolites were analyzed using a UHPLC coupled with a linear ion trap mass spectrometer, with the addition of hybrid ion trap-Orbitrap Mass Spectrometer when required. Up to ∼24% of curcumin, ∼61% of demethoxycurcumin (DMC) and ∼87% of bis-demethoxycurcumin (Bis-DMC) were degraded by the human faecal microbiota after 24 h of fermentation in vitro. Three main metabolites, namely tetrahydrocurcumin (THC), dihydroferulic acid (DFA) and a metabolite with an accurate mass of 181.08734, which was tentatively identified as 1-(4-Hydroxy-3-methoxyphenyl)-2-propanol were detected in the fermentation cultures containing the curcuminoids. The data presented here provide insights into curcuminoid colonic metabolism, showing that bacterial breakdown products should be considered in further studies on both bioavailability bioactivity of curcumin.

Liquid-liquid extraction and liquid chromatography-mass spectrometry detection of curcuminoids from bacterial culture medium.

Liquid chromatography-mass spectrometry (LC-MS) has been used to detect polyphenolic curcuminoids found in turmeric but studies of metabolism by bacterial and mammalian cells in vitro are compromised by poor recovery from the culture medium. We report a liquid-liquid extraction procedure with ethyl acetate and use LC-MS to quantify extracted curcuminoids. Ethyl acetate allows recoveries of ∼ 80-86% of curcuminoids from the bacterial growth medium, bacterial cell lysate and combined bacterial cell and growth medium matrices; a clear improvement over acetonitrile where recoveries were ∼ 25-66%. This optimised method will enable studies of curcuminoid metabolism and may be applicable to other hydrophobic polyphenolic compounds.

Degradation of curcuminoids by in vitro pure culture fermentation.

Colonic bacteria may mediate the transformation of curcuminoids, but studies of this metabolism are limited. Here, the metabolism of curcuminoids by Escherichia fergusonii (ATCC 35469) and two Escherichia coli strains (ATCC 8739 and DH10B) was examined in modified medium for colon bacteria (mMCB) with or without pig cecal fluid. LC-MS analysis showed that 16-37% of curcumin, 6-16% of demethoxycurcumin (DMC) and 7-15% of bis-demethoxycurcumin (Bis-DMC), and 7-15% of bis-demethoxycurcumin (Bis-DMC) were converted following 36 h of fermentation, with the amount of curcuminoids degraded varying depending on the bacterial strain and medium used. Three metabolites (dihydrocurcumin (DHC), tetrahydrocurcumin (THC), and ferulic acid (FA)) were found in fermentation cultures with all strains used. In addition, a compound with m/z [M - H](-) 470 was found and identified to be a curcumin adduct (curcumin-l-cysteine), using accurate mass FT-ICR-MS. This study provides insights into the bacterial metabolism of curcuminoids.