Bioconversion de l'acide p-coumarique par Brettanomyces ...

ethanol before to be added in different concentrations in a synthetic winemedium. Two minutes after, a sample was taken and centrifuged. The liquidpart was tested on HPLC to detect the p-coumaric acid concentration, and onGC/MS to detect the 4-vinylphenol and 4-ethylphenol content. All the testswere compared with witness samples free of yeast.2.2. Adsorption tests on PVPP and yeast cell wallsPolyvinylpolypyrrolidone (PVPP) and yeast cell walls were used as twooenological adsorbent in the concentration of 3 g/L.The medium used was a synthetic wine medium free of p-coumaric acid. A 2 3factorial experimental design was tested to study the variation of the adsorbedquantity Qe (mol/g) of p-coumaric acid added in different concentrations.Q e = X/m, where m is the adsorbent mass, and X = Ci (initial concentration) - C e(concentration at equilibrium).The factors tested were the pH (3- 3.5 – 4), the temperature (25, 30, 35 o C) andthe ethanol concentration (10- 11.5- 13 % v/v). The agitation was fixed at 250rpm. All the tests were compared with witness samples free of adsorbent. Thep-coumaric acid concentrations tested were 2.5 and 20 mg/L, for each adsorbentand for each level of the experimental design. The contact time for adsorptionwas 5h.3. RESULTS AND DISCUSSION3.1 Adsorption tests in fermentationsResults showed a difference in the adsorption potential of each species. In fact,the brettanomyces sp. showed a better adsorption than the saccharomyces intheir specific conditions (Table 1). There was no 4-vinylphenol or 4-ethylphenol production, corresponding to the lost p-coumaric acid in the contactperiod (2min).Table 1 - Adsorption of p-coumaric acid on Brettanomyces sp. andSaccharomyces sp. in fermentation conditionsInitial concentrationp-coumaric (mg/L)Concentration foundp-coumaric (mg/L)Population(10 6 Cell/ml)Saccharomyces 10 9,83 6010 9,53 12010 9,09 240Brettanomyces 10 9,1 310 8,4 36010 5,2 450These results confirmed the bibliography datas [7]. In fact, the p-coumaric acidis the less adsorbed phenolic acid by the saccharomyces sp. Its adsorption onbrettanomyces cell walls was recently defined [8].3.2 Adsorption tests on PVPP and yeast cell walls