Evaluation of current operating standards for chlorine dioxide in disinfection of dump tank and flume for fresh tomatoes.

Standard postharvest unit operations that rely on copious water contact, such as fruit unloading and washing, approach the criteria for a true critical control point in fresh tomato production. Performance data for approved sanitizers that reflect commercial systems are needed to set standards for audit compliance. This study was conducted to evaluate the efficacy of chlorine dioxide (ClO(2)) for water disinfection as an objective assessment of recent industry-adopted standards for dump tank and flume management in fresh tomato packing operations. On-site assessments were conducted during eight temporally distinct shifts in two Florida packinghouses and one California packinghouse. Microbiological analyses of incoming and washed fruit and dump and flume system water were evaluated. Water temperature, pH, turbidity, conductivity, and oxidation-reduction potential (ORP) were monitored. Reduction in populations of mesophilic and coliform bacteria on fruit was not significant, and populations were significantly higher (P < 0.05) after washing. Escherichia coli was near the limit of detection in dump tanks but consistently below the detection limit in flumes. Turbidity and conductivity increased with loads of incoming tomatoes. Water temperature varied during daily operations, but pH and ORP mostly remained constant. The industry standard positive temperature differential of 5.5°C between water and fruit pulp was not maintained in tanks during the full daily operation. ORP values were significantly higher in the flume than in the dump tank. A positive correlation was found between ORP and temperature, and negative correlations were found between ORP and turbidity, total mesophilic bacteria, and coliforms. This study provides in-plant data indicating that ClO(2) can be an effective sanitizer in flume and spray-wash systems, but current operational limitations restrict its performance in dump tanks. Under current conditions, ClO(2) alone is unlikely to allow the fresh tomato industry to meet its microbiological quality goals under typical commercial conditions.

Detection of Shiga toxin-producing Escherichia coli O26, O45, O103, O111, O113, O121, O145, and O157 serogroups by multiplex polymerase chain reaction of the wzx gene of the O-antigen gene cluster.

O-antigens on the surface of Escherichia coli are important virulence factors that are targets of both the innate and adaptive immune system and play a major role in pathogenicity. O-antigens that are responsible for antigenic specificity of the strain determine the O-serogroup. E. coli O26, O45, O103, O111, O113, O121, O145, and O157 have been the most commonly identified O-serogroups associated with Shiga toxin-producing E. coli (STEC) implicated in outbreaks of human illness all over the world. A multiplex polymerase chain reaction assay was developed to simultaneously detect the eight STEC O-serogroups targeting the wzx (O-antigen-flippase) genes of all O-antigen gene clusters. The sensitivity of the multiplex polymerase chain reaction was found to be 10 colony forming units for each O-group when enriched in broth and 100 colony forming units when enriched in artificially inoculated apple juice diluted with tryptic soy broth for 16 h at 37°C. The method can be used for detecting STEC O-groups simultaneously and may be exploited for improving the safety of food products.

Multiplex PCR detection of Shiga toxin-producing Escherichia coli strains belonging to serogroups O157, O103, O91, O113, O145, O111, and O26 experimentally inoculated in beef carcass swabs, beef trim, and ground beef.

Numerous foodborne outbreaks are attributed to Shiga toxin-producing Escherichia coli (STEC) and have been recognized for causing gastrointestinal disease in humans. Beef products have been considered the principal source of STEC. A multiplex PCR assay enabling simultaneous detection of STEC O103, O91, O113, O145, O111, O157, and O26 was developed and evaluated in artificially contaminated beef carcass swabs, beef trim, and ground beef after overnight enrichment. Individual serogroups were experimentally inoculated at low (1 to 10 CFU/ml) and high (11 to 100 CFU/ml) levels, and with a cocktail of strains belonging to two, four, and six serogroups. There was no significant difference in detecting single STEC strains under the different conditions. Only when strains were combined were there significant differences in detection of all cocktail isolates in some of the beef products. To address this issue, four serogroups were experimentally inoculated together at three different estimated levels (10, 10(2), and 10(3) CFU/ml) in all three beef products. Results yielded no significant difference in detecting STEC at the three inoculation levels (10, 10(2), and 10(3) CFU/ml) in trim and carcass swabs, but there was a significant difference in detecting STEC at the lowest levels (10 and 10(2) CFU/ml) in the 80:20 nonirradiated ground beef, and in the detection of STEC in irradiated ground beef. The findings from this study could provide industry and government agencies with a tool to evaluate the prevalence and incidence of STEC in beef products and their processing environments.

Evanescent wave fiber optic biosensor for salmonella detection in food.

Salmonella enterica is a major food-borne pathogen of world-wide concern. Sensitive and rapid detection methods to assess product safety before retail distribution are highly desirable. Since Salmonella is most commonly associated with poultry products, an evanescent wave fiber-optic assay was developed to detect Salmonella in shell egg and chicken breast and data were compared with a time-resolved fluorescence (TRF) assay. Anti-Salmonella polyclonal antibody was immobilized onto the surface of an optical fiber using biotin-avidin interactions to capture Salmonella. Alexa Fluor 647-conjugated antibody (MAb 2F-11) was used as the reporter. Detection occurred when an evanescent wave from a laser (635 nm) excited the Alexa Fluor and the fluorescence was measured by a laser-spectrofluorometer at 710 nm. The biosensor was specific for Salmonella and the limit of detection was established to be 10(3) cfu/mL in pure culture and 10(4) cfu/mL with egg and chicken breast samples when spiked with 10(2) cfu/mL after 2-6 h of enrichment. The results indicate that the performance of the fiber-optic sensor is comparable to TRF, and can be completed in less than 8 h, providing an alternative to the current detection methods.