|Abstract or Summary
- Wine has recently been shown to be a possible protective agent against
microbial foodbome illness. The chemical environment of wine makes it difficult, if
not impossible, for microorganisms to survive. The low pH, high concentration of
organic acids, relatively high ethanol concentrations, and the potential for high levels
of sulfur dioxide provide a series of hurdles for any microorganism that comes into
contact with wine. Each and every wine contains a different amount of these known
antimicrobial parameters and the combination of these components contribute to its'
ability of to inactivate microorganisms. The objective of this research was to
determine the role these parameters contribute to the observed antimicrobial effect.
Initial experiments focused on the addition of sulfur dioxide to increase
antibacterial efficacy. Four bacterial strains of common household pathogens were
used to measure antimicrobial activity in a suspension test, Klebsiella pneumoniae,
Pseudomonas aeruginosa and two strains of Staphylococcus aureus. A Chardonnay
wine was produced at Oregon State University and different levels of sulfur dioxide
and 1.5% sodium chloride were added. As expected, different bacterial species
displayed varying levels of sensitivity towards the wine samples. Kiebsiella
pneumoniae and P. aeruginosa were significantly more sensitive to wine than S. aureus. The former strains were inactivated by all treatments in less than five
minutes. Staphylococcus aureus cells were capable of surviving in some of the wine
treatments for nine minutes. Increased sulfur dioxide concentration and the presence
of sodium chloride enhanced the ability of wine to inactivate these microorganisms.
Five commercial Chardonnay wines were analyzed for their ability to
inactivate the most resistant strain S. aureus 649. Samples were enumerated after one
and three minutes of exposure. Results were variable, however trends could be
discerned. Sulfur dioxide concentration did not correlate with antimicrobial activity of
the wines. Other wine components were measured: pH, titratable acidity, volatile
acidity, and ethanol concentration. No single parameter correlated with efficacy from
the suspension tests. It was determined that complex interactions between wine
components and their availability for acting on the microorganism varied by wine
system. It is possible that there are other wine components that contribute to efficacy
that were overlooked (e.g. polyphenols).
The final stage of this study involved evaluating combinations of pH, titratable
acidity, sulfur dioxide, and ethanol in a wine background. Suspension tests were
performed against Escherchia coli 01 57:H7 and Staphylococcus aureus with samples
being taken after twenty minutes of exposure. Escherichia coli 01 57:H7 was
significantly more sensitive than S. aureus to the wine treatments. Analysis of overall
trends showed that titratable acidity and ethanol concentration were not ideal
predictors of efficacy. Molecular sulfur dioxide concentration was found to be a
relatively good predictor of antimicrobial effects. Hydrogen ion concentration (pH)
levels appear to be the most important parameter for predicting inactivation of S. aureus. Varying pH levels are known to affect the antimicrobial effects of other
components. Decreased pH shifts the equilibrium of organic acids to the more
antimicrobial undissociated form. Decreasing pH also increases the concentration of
molecular sulfur dioxide in solution. The antimicrobial effects of ethanol are known
to be enhanced by lowering the pH of the solution. This study concluded that
decreasing pH enhanced the antimicrobial effect of ethanol. Other combinations may
also lead to some strong conclusions that may enhance the ability to predict
disinfection ability of a given wine.
Overall results suggest that Chardonnay wine contains a combination of
antimicrobial parameters that contribute to disinfecting ability. Of the tested
parameters, pH appears to be the most influential; however the combination of all the
components is more important than any one parameter.
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