Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 1995
Publication Date: N/A
Interpretive Summary: Fresh-cut vegetables provide a desirable media for growth of microorganisms due to open tissues and can possibly harbor food borne pathogens, both are undesirable. A study was made to determine the identity and population of microorganisms on stored fresh-cut spinach, which would be helpful in determining which microorganisms are responsible for deterioration of spinach and to determine if commercially prepared fresh-cut spinach was contaminated with food borne pathogens. Large populations of 7 different types of microorganisms were identified and 4 of them increased sharply during 12 days storage of spinach at 10 degrees C. No Listeria or Salmonella were detected. Scanning electron micrographs of the spinach indicated that most of the microorganisms were inside the leaves, and not on the surface. This information will be useful to to scientists and industry in developing methods to control the microorganisms.
Technical Abstract: The microbial population found on fresh-cut spinach leaves that were stored in gas permeable bags at 10 degrees C for 12 days were examined and identified. The microorganisms consisted of mesophilic aerobic flora, psychrotrophic flora, Pseudomonadaceae, Enterobacteriaceae, Micrococcaceae, lactic acid bacteria and yeasts. Populations of mesophiles, psychrotrophs, ,pseudomonadaceae and Enterobacteriaceae increased sharply during the storage period. The initial concentrations were 1 E+07, 1 E+06, 1 E+06 and 1 E+04 CFU.g-1 respectively. Concentrations reached 1 E+10 for the mesophiles, psychrotrophs and Pseudomonadaceae and 1 E+07 CFU.g-1 for Enterobacteriaceae after 12 days of storage. Micrococcaceae, lactic acid bacteria and yeasts remained constant (1 E+03 to 1 E+04 CFU.g-1). The majority of the bacterial isolates were identified as Pseudomonas fluorescens, Aeromonas caviae and Staphylococcus xylosus. The yeasts, which were most frequently isolated, were classified in the genus Cryptococcus. No pathogens such as Listeria monocytogenes and Salmonella were detected. Observations with low temperature scanning electron microscopy (LTSEM) indicated that the microorganisms were not present on the surface of healthy unbroken leaves. Alternatively, they were found in areas where the cuticle was broken and could be seen infecting the internal palisade parenchyma.