Antimicrobial efficacy of vacuum impregnation washing with malic acid applied to whole paprika, carrots, king oyster mushrooms and muskmelons

Antimicrobial effect of vacuum impregnation (VI) applied to organic acid washing against Salmonella Typhimurium, Escherichia coli 0157:H7 and Listeria monocytogenes on paprika fruit, carrots, king oyster mushrooms and muskmelons was investigated. Samples were treated with intermittent VI with 21.3 kPa and compared with dipping washing in 2% malic acid. The initial sample pathogen levels were approximately 10(5)-10(7) CFU/cm(2). Enumerations of the three pathogens on paprika and carrots treated with VI washing were reduced to below the detection limit (= 1 logo CFU/cm(2)) after 3-5 min and 15 20 min, respectively. For each time point where populations of the three pathogens were reduced to below the detection limit by VI treatment, populations of 1.2-1.9 log CFU/cm(2) and 2.5 to 2.8 log CFU/cm(2) survived on paprika and carrots, respectively, when subjected to dipping treatment. After 20 min of dipping treatment, surviving populations of the three pathogens ranged from 3.5 to 4.1 and 33 to 4.4 log CFU/cm(2) on king oyster mushrooms and muskmelons, respectively. After 20 min of VI treatment, surviving populations of the three pathogens ranged from 3.0 to 3.6 log and 3.1 to 4.1 log CFU/cm(2), respectively, on king oyster mushrooms and muskmelons. Additionally, there were no significant (P >= 0.05) differences in pathogen reductions between dipping and VI treatment for both king oyster mushrooms and muskmelons. King oyster mushrooms (R-alpha = 6.02 +/- 1.65 mu m) and muskmelons (R-alpha = 11.43 +/- 1.68 mu m) had relatively large roughness values compared to those of paprika (R-alpha = 0.60 +/- 0.10 mu m) and carrots (R-alpha = 2.51 +/- 0.50 mu m). Scanning electron photomicrographs showed many deep protected sites in king oyster mushrooms and muskmelons with many microbes located deep in these sites following VI treatment. Instrumental color, texture and titratable acidity values of paprika and carrots subjected to VI washing treatment with 2% malic acid for 5 and 20 min were not significantly (P >= 0.05) different from those of untreated control samples during 7 day storage. (C) 2017 Published by Elsevier Ltd.