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Enhanced antimicrobial effect of organic acid washing against foodborne pathogens on broccoli by vacuum impregnation

Kang, Jun-Won, Kang, Dong-Hyun
International journal of food microbiology 2016 v.217 pp. 85-93
Listeria monocytogenes, Salmonella Typhimurium, anti-infective properties, bacteria, broccoli, cell suspension culture, color, dipping, food pathogens, malic acid, sanitizers, texture, titratable acidity, washing
This study was undertaken to evaluate the effect of vacuum impregnation applied to the washing process for removal of Salmonella Typhimurium and Listeria monocytogenes from broccoli surfaces. Broccoli was inoculated with the two foodborne pathogens and treated with simple dipping washing or with vacuum impregnation in 2% malic acid for 5, 10, 20, or 30min. There were two methods of vacuum impregnation: continuous and intermittent. After 30min of 101.3kPa (=14.7psi, simple dipping), 61.3kPa (=8.9psi), and 21.3kPa (=3.1psi) of continuous vacuum impregnation treatment, there were 1.6, 2.0, and 2.4log10CFU/g reductions of S. Typhimurium and 1.5, 1.7, and 2.3log10CFU/g reductions of L. monocytogenes, respectively. After 30min of 101.3, 61.3, and 21.3kPa of intermittent vacuum impregnation treatment, there were 1.5, 2.3, and 3.7log10CFU/g reductions of S. Typhimurium and 1.6, 2.1, and 3.2log10CFU/g reductions of L. monocytogenes, respectively. Scanning electron photomicrographs showed that bacteria tend to attach to or become entrapped in protective sites after simple wash processing (dipping). However, most bacteria were washed out of protective sites after intermittent treatment. Direct treatment of cell suspensions with vacuum impregnation showed that it had no inactivation capacity in itself since there were no significant differences (P≥0.05) between the reduction rates of non- and vacuum impregnation treatment. These results demonstrate that the increased antimicrobial effect of vacuum impregnation can be attributed to increased accessibility of sanitizer and an enhanced washing effect in protected sites on produce. Color, texture and titratable acidity values of broccoli treated with intermittent vacuum impregnation in 2% malic acid for 30min were not significantly (P≥0.05) different from those of untreated samples even though a storage interval was needed for titratable acidity values to be reduced to levels comparable to those of untreated controls.