Date of Award

8-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

P. Michael Davidson

Committee Members

David Golden, John R. Mount

Abstract

Studies were conducted to test the efficacy of several common household products containing antimicrobial compounds for inactivating spores of Bacillus cereus, as a surrogate for B. anthracis, on fresh fruit or vegetables. Additionally, the effect of storage time on hypochlorite activity of household products was determined. Bacillus cereus ATCC 33018 and ATCC 49064 were used in a cocktail for all tests. Household disinfectant and/or cleaning products with potential for sanitization were purchased in a retail market and were selected based upon efficacy against B. cereus in previous tests in milk. The active components were NaOCl, HCl or H2O2. For produce, cantaloupe melons and spinach were obtained from a local retail market and rinsed with sterile deionized (DI) water. Cantaloupe rinds were removed, trimmed to remove the mesocarp, cut into 25 cm2 sections and placed in sterile Petri dishes. Sections of melon and spinach leaves were spot inoculated with 0.1 ml of B. cereus and allowed to dry for 30 min at 25oC. Sanitizing products were sprayed onto the surface of the produce and the produce was allowed to stand for various times. Produce was then placed in neutralizer buffer to arrest the activity of sanitizing compounds and survivors were enumerated on non-selective media. To determine the effect of product age on activity, three commercial NaOCl-containing products that were past, at and 6 mo from the expiration dates were evaluated. Spinach and cantaloupe were tested as described previously. For the cantaloupe melon rind the control population mean was 7.15 + 0.07 log CFU/cm2. The log reduction was > 5.15 for undiluted NaOCl (Clorox®, 6.00% NaOCl) and inactivation took 120 min though the greatest reduction was observed in the first 10 min. For products containing 1.84%-2.40% NaOCl, log reductions were 2.75 to 3.40 over 180 min. For spinach, the control population mean was 7.37 + 0.01 log CFU/leaf. A > 5.84 log reduction in B. cereus spores was found for both undiluted NaOCl (Clorox®) and HCl (The Works Drain Opener, 20.00% HCl). However, the former reduced the viable spore population to the lowest detection level in 10 to 60 min while the latter took approximately 3 h. A 4.23-4.60 log reduction occurred with the 1.84%-2.40% NaOCl-containing products after 180 min. Hydrogen peroxide had the least effective sporicidal capabilities of the solutions tested reducing the population by less than 1 log. With respect to effect of storage on sporicidal activity of HOCl-containing products, samples stored up to 1 year past expiration were compared with those stored for 6 months prior to expiration and purchased fresh. There was no significant difference in the in vitro inactivation of B. cereus spores among the products. B. cereus spores were inactivated to below detectable levels after 1 min in 50% and 25% commercial strength solutions (>4.0 log CFU/ml). These findings were confirmed utilizing cantaloupe rind and spinach leaves treated with HOCl-containing products of the same storage times. B. cereus spores were inactivated to below the level of detection (>5.84 log CFU/cm2, >5.15 log CFU/cm2) in 10 min and 60 min for spinach and cantaloupe respectively, regardless of compound age.

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