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

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With the methodology of factorial experimental design, the values of Qe wereassimilated to a first degree polynomial model:Qe = ao + a 1 X 1 + a 2 X 2 + a 3 X 3 + a 4 X 1 X 2 + a 5 X 1 X 3 + a 6 X 2 X 3 + a 7 X 1 X 2 X 3 ± ε,where X 1 was Temperature, X 2 was pH and X 3 was the ethanol concentration.The aim of this polynomial model was to join the effect of each factor on Qewith the effect of the interactions.The EXCEL STAT 2003 as well as the STATGRAPHICS were used to analysethe complete factorial design results. The determination of the polynomialcoefficient was achieved by a multilinear regression multivariable analysis. Thevariances of the parameters were calculated by an ANOVA test, in the aim todetermine the significance of the effects.The Student test (t) was acquired at a 3 freedom degree level, and for aconfidence level of 95%. The values of polynomial coefficients wereconsidered significant when the student test was higher than 3,18. The R 2coefficient represents the potential of the polynomial equation to predict theeffect of the factors.The statistical analysis results are presented in the Pareto graphs in figure 1when PVPP was used. The factor effects were presented for two concentrationsof p-coumaric acid: 2.5 and 20 mg/L.When PVPP was the adsorbent, only the temperature had a significant effect onadsorption in the tested conditions. The p-coumaric acid adsorption wasimproved when the temperature increased from 25 to 35°C. The ethanolconcentration, as well as the pH, had no direct effect on the adsorption, on thetwo p-coumaric concentrations levels. The R 2 values were 0.92 for pareto (a)and 0.97 for pareto (b), which indicates the good performance of the tests.P = 0.05TemperaturepHEtOHT*pHT*EtOHpH*EtOHT*pH*EtOH(a)P = 0.05TemperaturepHEtOHT*pHT*EtOHpH*EtOHT*pH*EtOH(b)Figure 1- Estimated effect of the factors on Qe when PVPP was the adsorbent –(a) 20 mg/L p-coumaric acid, (b) 2.5 mg/L p-coumaric acid.
On the other hand, when the yeast cell walls were the adsorbent, experimentalresults were less reproducible. The interpretation of pareto graphs was moredifficult and all the factors seemed to affect the Qe.Nevertheless, it was possible to compare the capacity of adsorption of PVPPand yeast extract. With the same concentration of each (3g/L), PVPP wasalways a better adsorbent than yeast extract. For instance, at 25 o C, themaximum loss of p-coumaric acid by adsorption was 69% ± 1% and 99.4 % ±8.4 respectively for 20 and 2.5 mg/L when the PVPP was the adsorbent whereasthe maximum loss of p-coumaric acid was 45% ± 12% and 72% ± 37% whenthe yeast cell walls were the adsorbent (respectively for 20 and 2.5 mg/L).,.4. CONCLUSIONThe p-coumaric acid showed different adsorption profiles on different yeastspecies. The brettanomyces sp. had a better adsorption potential of the p-coumaric acid than the saccharomyces sp. Because of its partial adsorption onyeast, the p-coumaric acid present in wine cannot be transformed totally into 4-vinylphenol and 4-ethylphenol.The p-coumaric acid removal from the medium will avoid the horse sweat smellodours if a contamination occurs. Its adsorption on oenological components canbe a solution to avoid its bioconversion.The two adsorbent materials tested showed that the PVPP is a better adsorbentthan yeast cell walls of this acid in wine conditions. The non significanceeffects of the factors pH and ethanol concentration on the p-coumaricadsorption by PVPP was proved. On the other hand, increasing the temperaturefrom 25 to 35°C favoured the adsorption on PVPP. Finally, it was shown withPVPP, that it is possible to decrease drastically the p-coumaric acidconcentration in a synthetic wine medium.The p-coumaric acid adsorption on PVPP in true wine is being studied, as a firststep of industrial application.REFERENCES(1) P. Chatonnet, C. Viala, D. Dubourdieu. Am. J. Enol. Vitic. 48 (1997)443-448.(2) D. M. Goldberg, E. Tsang, A. Karumanchiri, G. J. Soleas. Am. J. Enol.Vitic. 49 (1998) 142-151.(3) P. Chatonnet, D. Dubourdieu, J.N. Boidron, M. Pons. J. Sc. of FoodAgric. 60(1992) 165-178.(4) L. Dias, S. Pereira-da-Silva, M. Tavares, M. Malfeito-Ferreira, V.Loureiro. Food Microbiol. 20(2003) 377–384.(5) D. Chassagne, M. Guillou-Benatier, H. Alexandre, A. Voilley. Foodchem. 91(2005)39-44(6) A. Morata, M.C. Gomez-Cordoves, J. Suberviola, B. Bartolomé, B.Colomo, J.A. Suárez. J. Agric. Food Chem. 51(2003) 4084-4088.(7) S. Razmkhab, A. Lopez-Toledano, J.M. Ortega, M. Mayen, J. Merida,M. Medina. J. Agric. Food Chem, 50(2002), 7432-7437.(8) D. Salameh, C. Brandam, W. Medawar, R. Lteif, P. Strehaiano. FoodChem.107(4)(2008) 1661-1667.
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Bioconversion de l'acide p-coumarique par Brettanomyces ...

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