BIOSORPTION OF UNDESIRABLE COMPONENTS FROM WINE BY YEAST-DERIVED PRODUCTS

Abstract

4-Ethylphenol (EP) in wine is associated with organoleptic defects such as barn and horse sweat odors. The origin of EP is the bioconversion reaction of p-coumaric acid (CA), naturally present in grapes and grape musts by contaminating yeasts of the genus Brettanomyces bruxellensis.

Yeast cell walls (YCW) have shown adsorption capacities for different compounds. They could be applied to wines in order to adsorb either CA and/or EP and thus reduce the organoleptic defects caused by the contaminating yeasts.

In this work, we selected four YCW derived from two different yeast genera (Brettanomyces/Dekkera and Saccharomyces) prepared by two processes, autolysis or with a high-pressure homogenizer (HPH). We investigated the effects of both genus and treatment on the capacity of adsorption of CA and EP. The operating parameters affecting adsorption, such as contact time, sorbent dosage, and initial CA and EP concentration, were studied to evaluate their influence on the adsorption capacity. The competition between the two adsorbates on the sorption sites was also investigated.

The adsorbed amounts of CA and EP by the YCW increased as the concentration of the adsorbent increased, regardless of their initial concentration. This might be explained by the increase in active vacant sorption sites and surface area available for the adsorption of CA and EP.

At equilibrium, the specific adsorption capacity of YCW increased when the initial concentration of adsorbate increased. The resistance to mass transfer of the adsorbate between liquid and solid phases is overcome by the driving force, which is determined by the initial concentration of the adsorbate. As the adsorbate’s initial concentration increased, the concentration gradient’s driving force increased, which explains the increase in adsorption.

The specific adsorption capacity decreased when the two adsorbates were together in the medium. First, the adsorption capacity of EP is higher than CA, indicating that EP has specific sites on the YCW that are different from CA. Second, the adsorption capacity is higher when the adsorbate is alone in the medium, implying competition between the two adsorbates. There are probably some common sites for CA and EP on YCW.