Fresh produce sanitization by combination of gaseous ozone and liquid sanitizer

• E coli O157:H7 count reduction greatest with liquid sanitizer followed by vacuum cooling and ozonation.
• Sanitizer application after vacuum cooling and ozonation is less effective.
• Liquid sanitizer application followed by long-term gaseous ozone decreased E coli O157:H7 to undetectable levels.
• Long exposure time to sanitizers leads to some damage of spinach leaves.
• Combination of liquid and long-term ozone treatment is synergistic.

The effect of different combinations of gaseous ozone and Pro-San L against Escherichia coli on baby spinach was investigated. Three different ways to combine liquid and gaseous sanitizer application were compared. The most effective combination was the initial spray application of Pro-San L (0.66% Citric acid, 0.036% SDS) followed by vacuum cooling and ozonation under pressure of 68.9 kPa (10 PSIG) which reduced E. coli O157:H7 counts by 3.9 log CFU/g. Spray application of Pro-San L after the gaseous ozone injection under vacuum followed by immediate system pressurization to 68.9 kPa was less effective (2.7 log CFU/g reduction) due to vacuum internalization of bacteria deeper into produce tissue. This method was not significantly different from a single application of liquid sanitizer. Spray Pro-San L application followed by a long term (up to three days) gaseous ozone treatment decreased microbial load to an undetectable level after the first day of application. However the increase of exposure time to sanitizers led to some damage of spinach leaves. Long term combination liquid-gaseous sanitizer treatment resulted in better appearance of fresh produce than a single application of liquid and gaseous sanitizers.