Growth and 4-Ethylphenol Production by the Yeast<i>Pichia guilliermondii</i>in Grape Juices

Abstract

The behavior of <i>Pichia guilliermondii</i> strains producing high levels of 4-ethylphenol in synthetic media was studied in wines and grape juices. These strains lost their viability and did not produce 4-ethylphenol after 24 hr of inoculation in red wines with ethanol adjusted to 10 or 12% (v/v) and pH 3.5 in the absence of free sulfite. Under the same conditions, at 12% (v/v) ethanol, growth of <i>Dekkera bruxellensis</i> was observed. When grown in single culture in grape juices, selected strains of <i>P. guilliermondii</i> produced high levels of 4-ethylphenol. In mixed grape juice fermentations with <i>Saccharomyces cerevisiae</i>, <i>P. guilliermondii</i> began to die after starter inoculation at 10⁷ cfu/mL and did not produce 4-ethylphenol. Low starter inoculation rates (10² cfu/mL) added 72 hr after <i>P. guilliermondii</i> inoculation resulted in high production of 4-ethylphenol. In conditions mimicking cold prefermentative maceration processes, at 10°C for 72 hr, <i>P. guilliermondii</i> did not grow, while at 25°C growth attained a 10⁴-fold increase. At this temperature, addition of 200 mg/L potassium metabisulfite after grape crushing did not eliminate <i>P. guilliermondii</i> inoculated at 10⁴ cfu/mL in grape juice of pH 3.57. The possibility that high levels of 4-ethylphenol in wines are due to the activity of <i>P. guilliermondii</i> should be mostly related with uncontrolled growth in contaminated grape juices before starter inoculation. In wines, its ability to produce 4-ethylphenol seems to be much lower than that of <i>D. bruxellensis</i>.