- There have been several epidemiological studies linking alcohol
consumption to a decreased risk of contracting illness from foodborne
bacterial contamination. To study this phenomenon, we examined the
survival of Escherichia coli 0157:H7 and Salmonella typhimurium in grape
juice and wine and then designed a model stomach to investigate the effect
of wine consumption with a meal on the survival of these bacteria. In
addition, we looked at the role and relative effects of wine acid and alcohol
content on bacterial survival.
To test the relative role of acid and alcohol content on bacterial
survival, 500 mL aliquots of Chardonnay and Pinot Noir wines were
vacuum distilled to produce a non-volatile fraction containing only acids
and a volatile fraction containing only alcohol. These fractions were
subsequently brought back to the original 500 mL volume with distilled
water. For the survival studies, approximately 1 x 10⁷ CFU/mL of E. coli
0157:H7 or Salmonella was added directly to 25 mL of sterile-filtered
Chardonnay and Pinot Noir juice, wine, non-volatile, and volatile fractions.
These treatments were then plated on tryptic soy agar (TSA) at appropriate
time intervals to determine maximum survival times. We observed that
both E. coli 0157:H7 and S. typhimurium were inactivated in wine within 60 min. In grape juice, £. coli and S. typhimurium survived 3-12 d and 3 h-16 d,
respectively. Survival in the volatile fractions was less than 48 h for both
bacteria and in the non-volatile fractions E. coli and S. typhimurium both
survived less than 24 h.
To determine the antimicrobial effect of wine on the survival of food
borne E. coli 0157:H7 and S. typhimurium we designed a model stomach
system. In this system, varying amounts of jarred baby food, synthetic
gastric fluid (SGF), and the test beverage were aseptically placed in a
stomacher bag, inoculated with bacteria to a level of approximately 1 x 103
CFU/mL, and then mixed in a stomacher blender prior to each sampling.
The stomacher bags were sampled at 0, 30,60,120, and 180 min by the pour
plate method using TSA. The beverages tested in this system were
Chardonnay and Pinot Noir wines and their respective fractions; water
served as a control. Escherichia coli 0157:H7 showed little change in cell
population when in the presence of 150 g SGF, 150 g food, and 50 g of test
beverage, regardless of the beverage. Salmonella typhimurium, under the
same conditions, showed a marked difference between test beverages. In
the presence of 50 g of wine, S. typhimurium had a 66-100% reduction at 60
min and had attained 100% reduction after 120 min; without wine, a 33-94%
reduction was attained at 60 min and a 60-99% reduction was attained at
120 min. In general we found that that the E. coli 0157:H7 was much more
resistant to inactivation than was S. typhimurium in the model stomach.
Also, we found that Chardonnay was more effective in inhibiting bacteria
than Pinot Noir and that the non-volatile wine fractions were more
inhibitory than the volatile fractions. These observations suggest that the
antibacterial power of wine is highly acid dependent and that the
consumption of wine with a meal may afford protection against certain
types of food contamination.