and herbs prepared from plant parts owe some of their desired sensory attributes to these antimicrobials . Like organic acids, these compounds are released from cut tissues and may be lethal to microorganisms naturally occurring or intentionally inoculated onto fruits and vegetables.
Compounds involved in plant defense mechanisms have been classified as prohibitins, inhibitins, postinhibitins, or phytoalexins, depending on preinfec-tion or postinfection factors . These compounds may also kill or inhibit test microorganisms or microflora naturally present on produce. Table 24.4 lists some antimicrobials other than major flavor and aroma compounds that are known to be naturally present in raw fruits and vegetables or produced as a result of breakage of tissues or infections with bacteria and molds. These antimicrobials may interfere with detection and enumeration of bacteria capable of causing human illnesses.
Several studies have investigated inhibitory or lethal activities of naturally occurring antimicrobials against foodborne pathogenic and spoilage microorganisms. A study to compare washing in 0.1% peptone, stomaching, and homogenizing for their influence on recovery of salmonella inoculated onto 26 types of fruits, vegetables, and herbs, revealed that, overall, no significant differences in recovery of the pathogen could be attributed to a particular sample processing method . In an attempt to determine if exposure of salmonella to low pH of tissue fluids as a result of stomaching or homogenizing samples was lethal to the pathogen, the 26 types of produce were arbitrarily separated into groups based on pH. Significantly higher percent recoveries were obtained in produce in the pH 5.53 to 5.99 range compared to produce in lower pH ranges. Reduced percent recoveries from herbs (pH 5.94 to 6.34) were attributed in part to antimicrobials released from plant cells during sample preparation. The mean pH of herbs was 6.08. Lethality caused by antimicrobials other than acids in herbs may have been masked by the minimal inhibitory affect of this slightly acidic pH, causing a reduction in the number
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