Submitted to: Journal of Food Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2004
Publication Date: 1/1/2005
Citation: Reina, L.D., Breidt, F., Fleming, H.P., Kathariou, S. 2005. Isolation and selection of lactic acid bacteria as biocontrol agents for nonacidified, refrigerated pickles. Journal of Food Science. 70:M7-M11. Interpretive Summary: This research describes the use of lactic acid bacteria to prevent the growth of organisms that cause diseases in foods by bacterial competition. Our objective was to control the bacterial ecology of ready-to-eat vegetable products so that when these foods spoil (as all foods will eventually), lactic acid bacteria which are harmless to humans or even helpful as probiotics will predominate and prevent the growth of dangerous bacteria. This method of insuring food safety by bacterial competition is called biocontrol. We isolated over 100 potential biocontrol bacteria from a non-acidified deli-type pickle product and used this product as a model system for studying biocontrol. The cultures were tested under temperature abuse conditions for the ability to prevent the growth of Listeria monocytogenes in the product. Several lactic acid bacteria isolates showed ideal characteristics for use as biocontrol cultures. These cultures and the methodology used for their isolation and characterization may have broad application for use in ready to eat vegetable products.
Technical Abstract: A deli-type pickle product was used as a model system to study the potential for use of biocontrol to prevent the growth of pathogens in minimally processed fruits and vegetables (MPFV). Fresh pickling cucumbers were blanched at 80 deg C for 15 sec, cooled, and brined to equalize at 2% NaCl in 1.4-L glass jars. Sterile spices and garlic oil were added to prevent microbial contamination from the ingredients. The product was stored at 5 deg C for 3 weeks and then transferred to various abuse temperatures (16, 25, 30 deg C). Bacteria that grew on MMRS (modified MRS) agar plates were isolated, Gram stained, and biochemically characterized by gas production, as well as oxidase and catalase reactions. They were also characterized and putatively identified using molecular techniques. They were grouped according to their intergenic transcribed spacer region (ITS)-PCR and RsaI restriction endonuclease profiles and further identified to species level by sequencing the variable regions V1 and V2 of the 16S rRNA gene. The isolates were also tested for bacteriocin-like production against Gram-positive and Gram-negative bacteria. A total of 118 lactic acid bacteria (LAB) were isolated from the product. Among the LAB identified were Lactococcus, Leuconostoc, Lactobacillus, Weissella, and Enterococcus spp. Six putative isolates (Lactococcus) produced bacteriocin-like activity against other LAB and Listeria. The addition of a bacteriocin-producing LAB or their metabolites, if effective against food pathogens, may improve the safety of minimally processed vegetable products.