Comparison of spot, spray, and dip inoculation methods to determine efficacy of chlorine dioxide gas and chlorinated water treatments in reducing Salmonella spp. on green peppers
Y. HAN, N. G. Bright, B. M. Applegate, R. H. Linton, P. E. Nelson
Book of Abstracts, 2004 IFT (Institute of Food Technologists) Annual Meeting and Food Expo, 13-16 July 2004, Las Vegas, Nevada, USA. 321 pages.
2004
บทคัดย่อ
Comparison of spot, spray, and dip inoculation methods to determine efficacy of chlorine dioxide gas and chlorinated water treatments in reducing Salmonella spp. on green peppersTo successfully evaluate efficacy of antimicrobial agents, it is necessary to develop a standardized inoculation method that best represents naturally existing bacteria on produce. Our objective was tocompare spot, spray, and dip inoculation to determine efficacy of chlorine dioxide (ClO2) gas and chlorinated water treatments in reducing Salmonella spp. on green peppers using a bacterial enumeration technique, cryo-scanning electronic microscopy (CSEM) and fluorescence microscopy (FM). A mixture of five strains of Salmonella spp. was used for inoculation while a green fluorescence protein-labeled Salmonella enteritidiswas used for FM. Peppers were spot-inoculated or spray-inoculated with 7-8 log cfu/cm2Salmonella, or dip-inoculated in 9 log cfu/ml bacterial suspension for 1 min, air-dried for 2 hrs or stored for 1 and 3 days at 4°C, and then treated with 0.3-0.6 mg/l ClO2 gas for 5-10 min or 200 ppm chlorinated water for 10 min, respectively. Bacterial populations were enumerated using tryptic soy agar followed by membrane-transferring plating on bismuth sulphiteor xylose lysine desoxycholateagars. After one day storage, recovered populations among three inoculation methods were not significantly different (P>0.05). After 3 day storage, the population for dip inoculation was the lowest compared to other methods. After 0.6 mg/1 ClO2 gas treatment for 10 min. the ranges of log reductions were 4-6, 3.5-4, and 2-3 log cfu for spot, spray, and dip inoculation, respectively. FM and CLSM studies demonstrated different bacterial distribution and viability after inoculation and ClO2 gas treatment. For 3-day stored samples, log reductions after 200ppm chlorinated water treatment were 3.9±0.3 for spot, 29±0.3 for spray, and 2.8±0.5 for dip. Important factors affecting antimicrobial efficacy of these treatments were identified as inoculation method, storage condition, and time. Results will help improve and ensure the safety of produce by using precisely defined and effective sanitation technologies, such as ClO2 gas treatment.