Masters Theses

Date of Award

5-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

David A. Golden

Committee Members

Kimberly Kelly-Wintenberg, Greg Hulbert

Abstract

Generation of a stable plasma under ambient conditions (One Atmosphere Uniform Glow Discharge Plasma - OAUGDP) has been developed and evaluated for sterilization of various surfaces. Research to determine the effects of the OAUGDP on foodborne pathogens is lacking. Thus, the objectives of this study were to determine the efficacy of the OAUGDP for inactivation of foodborne pathogens and to evaluate the influence of growth temperature, pH, and culture age on inactivation.

A wide variety of pathogens was used to test inherent differences among microorganisms. Escherichia coli 0157:H7, Listeria monocytogenes, Staphylococcus aureus. Bacillus cereus, Salmonella Enteritidis, Vibrio parahaemolyticus, Yersinia enterocolitica, Shigella flexneri, Clostridium sporogenes (surrogate for Clostridium botulinum), and Clostridium perfringens were evaluated. Three-strain mixtures of each bacterium were inoculated [6-7 log CFU/cm2 for all but Clostridium spp. (4-5 log CFU/cm2)] onto non-selective agar media adjusted to pH 5 or 7. Samples were exposed to the OAUGDP (0, control to 240 sec) immediately (within 30 min) or after incubation for 24 hr at 10 or 35°C. After exposure, the agar block was removed from slides and pummeled in 0.1% peptone water with a stomacher, serially diluted, surface plated onto non-selective media, and incubated at 35°C. Differences in pathogen survival as influenced by treatments were determined.

Exposure time, pH, incubation temperature, culture age, and all of the interactions affected survival of all pathogens exposed to the OAUGDP (P<0.05). The most significant reduction of pathogens generally occurred during the initial exposure period (30 or 90 sec) for all except Clostridium spp. which required altered methods due to anaerobic constraints and an initial exposure of 1 or 5 sec. Populations of pathogens incubated for 24 hr were more resistant than those exposed immediately after inoculation. Incubation at 35°C before exposure resulted in greater resistance to OAUGDP inactivation than incubation at 10°C. Incubation at 10°C on pH 5 media rendered the pathogens most susceptible to the OAUGDP. Typically, the non-linearity of inactivation curves was not conducive for determining meaningful Di-values over the entire inactivation curve. Therefore, Di-values (Di) were calculated using data from the unexposed controls and the initial exposure times. Initial inactivation differences among organisms were observed for 24-hr samples incubated at 35°C. Di-values for samples incubated at 35°C/pH 7 ranged from 810.81 sec (B. cereus) to 5.06 sec (C. perfringens) and from 271.08 sec (B. cereus) to 5.61 sec (C. sporogenes) for samples incubated at 35°C/pH 5. Overall, no appreciable differences in inactivation between Gram-positive and Gram-negative pathogens were observed, although the spore forming B. cereus was more resistant to the OAUGDP than non-spore formers and the anaerobic sporeformers.

These findings support the conclusion that we have demonstrated a potential for use of the OAUGDP as a treatment of foods for pathogen reduction. Increased sensitivity of pathogens to the OAUGDP at reduced pH and temperature is encouraging, since these conditions are applicable to many foods during processing, handling, and storage.

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