Whole-Leaf Wash Improves Chlorine Efficacy for Microbial Reduction and Prevents Pathogen Cross-Contamination during Fresh-Cut Lettuce Processing

Abstract: Currently, most fresh-cut processing facilities in the United States use chlorinated water or other sanitizer solutions for microbial reduction after lettuce is cut. Freshly cut lettuce releases significant amounts of organic matter that negatively impacts the effectiveness of chlorine or other sanitizers for microbial reduction. The objective of this study is to evaluate whether a sanitizer wash before cutting improves microbial reduction efficacy compared to a traditional postcutting sanitizer wash. Romaine lettuce leaves were quantitatively inoculated with E. coli O157:H7 strains and washed in chlorinated water before or after cutting, and E. coli O157:H7 cells that survived the washing process were enumerated to determine the effectiveness of microbial reduction for the 2 cutting and washing sequences. Whole-leaf washing in chlorinated water improved pathogen reduction by approximately 1 log unit over traditional cut-leaf sanitization. Similar improvement in the reduction of background microflora was also observed. Inoculated “Lollo Rossa” red lettuce leaves were mixed with noninoculated Green-Leaf lettuce leaves to evaluate pathogen cross-contamination during processing. High level (96.7% subsamples, average MPN 0.6 log CFU/g) of cross-contamination of noninoculated green leaves by inoculated red leaves was observed when mixed lettuce leaves were cut prior to washing in chlorinated water. In contrast, cross-contamination of noninoculated green leaves was significantly reduced (3.3% of subsamples, average MPN ≤−0.3 log CFU/g) when the mixed leaves were washed in chlorinated water before cutting. This result suggests that whole-leaf sanitizing washes could be a practical strategy for enhancing the efficacy of chlorine washes for pathogen reduction and cross-contamination prevention. Practical Application: Freshly cut leafy greens release large amount of organic matter that negatively impact the chlorine washing efficacy. Implementing the primary antimicrobial intervention step of chlorine washing prior to cutting can significantly improve the efficacy of microbial reduction and minimize pathogen cross-contamination.     

建立新型开放的自动化网络

本指出网络开放的重要性和意义,从结构上、设备上和网络的相互关系上分析了开放性,在此基础上,提出一个新型的工业自动化三层模型,作为建立新型自动化网络的基础。按此新三层模型建立的自动化网络,就是一个简单、开放的网络,以保证工业控制系统比较理想地运行。     

Feasibility of colloidal silver SERS for rapid bacterial screening

This study reports the feasibility of citrate-reduced colloidal silver surface-enhanced Raman scattering (SERS) for differentiating three important food borne pathogens, E. coli, Listeria, and Salmonella. FT-Raman and SERS spectra of both silver colloids and colloid-K₃PO₄ mixtures were collected and analyzed to evaluate the reproducibility and stability of silver colloids fabricated in a batch-production process. The results suggest that the reproducibility of the colloids over the batch process is high and that their binding effectiveness remains consistent over a 60-day storage period. Two specific SERS bands at 712 and 390 cm⁻¹ were identified and used to develop simple 2-band ratios for differentiating E. coli-, Listeria-, and Salmonella-colloid mixtures with a 100% success. These results indicate that colloidal silver SERS technique may be a practical alternative method suitable for routine and rapid screening of E. coli, Listeria, and Salmonella bacteria.     

A pilot plant scale evaluation of a new process aid for enhancing chlorine efficacy against pathogen survival and cross-contamination during produce wash

Developing food safety intervention technology that can be readily adopted by the industry often requires test conditions that match as closely as possible to those of commercial food processing operations; yet biosafety risks inherent in pathogen studies constrain most experiments to laboratory settings. In this study, we report the first semi-commercial pilot-scale evaluation of a new process aid, T128, for its impact on enhancing the antimicrobial efficacy of chlorinated wash water against pathogen survival and cross-contamination. A non-pathogenic, BSL-1, strain of Escherichia coli O157:H7 was inoculated onto freshly harvested baby spinach leaves and washed with large amounts of freshly cut un-inoculated iceberg lettuce shreds in wash water with free chlorine periodically replenished, in the presence or absence of T128. Changes in water quality and pathogen survival and cross-contamination were monitored at every 2min intervals for up to 36min for each treatment during the wash operation. Results indicated that the use of T128 did not significantly (P>0.05) influence the rate of wash water deterioration, nor the pathogen populations remaining on the inoculated spinach leaves. However, in the absence of T128 (control), survival of E. coli O157:H7 in wash water and cross-contamination of un-inoculated lettuce frequently occurred when free chlorine in solution dropped below 1mg/l during the wash process. In contrast, the use of T128 significantly reduced the occurrence of E. coli O157:H7 surviving in wash water and of cross-contamination to un-inoculated shredded iceberg lettuce under the same operational conditions, suggesting that the application of T128 in a chlorine-based fresh produce sanitization system could increase the safety margin of process control on fresh-cut operations.     

Development and evaluation of an on-line hide decontamination procedure for use in a commercial beef processing plantt

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/ 100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/100 cm2. The second objective was to evaluate the use of an on-line hide-wash cabinet that used a sodium hydroxide wash and a chlorinated (1 ppm) water rinse. Hides sampled before entering and after exiting the cabinet had aerobic plate counts and Enterobacteriaceae counts that were reduced by 2.1 and 3.4 log CFU/100 cm2, respectively, and the prevalence of E. coli O157 on hides was reduced from 44 to 17% when the cabinet was in use. Preevisceration carcass aerobic plate counts and Enterobacteriaceae counts were both reduced by 0.8 log CFU/100 cm2, and the prevalence of E. coli O157 on preevisceration carcasses was reduced from 17 to 2% when the cabinet was in use. These results support decontamination of hides as an effective means to reduce pathogen contamination of cattle carcasses during processing.     

Characterization of O157:H7 and other Escherichia coli isolates recovered from cattle hides, feces, and carcasses

In a previous study, the seasonal prevalence was reported for stx+ Escherichia coli O157:H7 in feces and on hides and carcasses of cattle at processing. Overall, 1,697 O157:H7 isolates have now been characterized for the incidence of (i) eae(O157), hlyA, stx1, and stx2 in the recovered isolates and (ii) presumptive rough and presumptive nonmotile isolates. Seven O157:H7 isolates (0.4%) lacked stx genes, although they carried eae and hlyA. All but one of the isolates carried both eae and hlyA. Approximately two-thirds of the isolates (64% when one isolate per sample was considered) carried both stx1 and stx2. E. coli O157:H7 cells that harbored both stx1 and stx2 were more often recovered from hides in the fall (79% of the fall hide isolates) and winter (84% of the winter hide isolates) than in the spring (53%) and summer (59%). Isolates recovered from preevisceration carcasses showed a similar but not statistically significant trend. Twenty-three of the 25 O157:H7 isolates carrying stx1 but not stx2 were recovered during summer. Fifteen presumptive rough and 117 presumptive nonmotile stx+ O157:H7 isolates were recovered. Ten (67%) of the presumptive rough isolates were recovered during summer. Ninety-five of the presumptive nonmotile isolates (81%) were recovered during fall. Forty-eight percent of the false-positive isolates (175 of 363) tentatively identified as O157:H7 were O157+ H7- and lacked eae(O157), hlyA, and stx. These data suggest that in beef processing samples (i) there are minor seasonal variations in the prevalence of stx genes among E. coli O157:H7 isolates, (ii) presumptive rough and presumptive nonmotile stx+ O157:H7 isolates are present, (iii) E. coli O157:H7 isolates lacking stx genes may be rare, and (iv) O157+ H7- isolates lacking stx genes can result in many false-positive results.     

Methods for recovering Escherichia coli O157:H7 from cattle fecal, hide, and carcass samples: sensitivity and improvements

The Meats Research Unit (MRU) methods, developed by MRU scientists of the U.S. Meat Animal Research Center, have been used to study the prevalence of Escherichia coli O157:H7 in cattle carcass, hide, and fecal samples. The sensitivity of these methods for recovery of injured E. coli O157:H7 cells from inoculated and uninoculated samples was determined, and potential improvements to these methods were evaluated. When using the conventional MRU methods, 91% of the pre-evisceration carcass samples tested positive for E. coli O157:H7 when inoculated with 5 to 10 CFU, 100% of hide samples tested positive for E. coli O157:H7 when inoculated with 30 to 50 CFU, and 96% of the fecal samples produced positive results when inoculated with 300 to 400 CFU per 10 g. The addition of a phosphate buffer to the tryptic soy broth enrichment improved recovery of E. coli O157:H7 from feces. Using the modified enrichment, 92% of the samples were identified as positive when inoculated with 10 to 30 CFU per 10 g. Substituting a commercially available wash buffer for the phosphate-buffered saline (PBS) plus Tween 20 wash buffer during immunomagnetic separation of hide samples improved recovery of the target organism at lower inoculum concentrations. When comparing uninoculated samples, substituting a PBS buffer plus a zwitterionic detergent for PBS plus Tween 20 also had a positive effect on recovery of E. coli O157:H7 from hide samples. Data presented here indicate that the MRU methods are highly effective at recovering injured E. coli O157:H7 from fecal, hide, and beef carcass samples; however, modifications can be added to increase the sensitivity.     

Effect of a reactive oxygen species-generating system for control of airborne microorganisms in a meat-processing environment

The effectiveness of reactive oxygen species (ROS)-generating AirOcare equipment on the reduction of airborne bacteria in a meat-processing environment was determined. Serratia marcescens and lactic acid bacteria (Lactococcus lactis subsp. lactis and Lactobacillus plantarum) were used to artificially contaminate the air via a six-jet Collison nebulizer. Air in the meat-processing room was sampled immediately after aerosol generation and at various predetermined times at multiple locations by using a Staplex 6 stage air sampler. Approximately a 4-log reduction of the aerial S. marcescens population was observed within 2 h of treatment (P < 0.05) compared to a 1-log reduction in control samples. The S. marcescens populations reduced further by approximately 4.5 log after 24 h of exposure to ROS treatment. Approximately 3-log CFU/m3 reductions in lactic acid bacteria were observed following 2-h ROS exposure. Further ROS exposure reduced lactic acid bacteria in the air; however, the difference in their survival after 24 h of exposure was not significantly different from that observed with the control treatment. S. marcescens bacteria were more sensitive to ROS treatment than the lactic acid bacteria. These findings reveal that ROS treatment using the AirOcare unit significantly reduces airborne S. marcescens and lactic acid bacteria in meat-processing environments within 2 h.     

Effects of low-dose, low-penetration electron beam irradiation of chilled beef carcass surface cuts on Escherichia coli O157:H7 and meat quality

Low-dose, low-penetration electron beam (E-beam) irradiation was evaluated for potential use as an antimicrobial intervention on beef carcasses during processing. The objectives of this study were (i) to assess the efficacy of E-beam irradiation to reduce concentrations of Escherichia coli O157:H7 on a large beef surface and (ii) to evaluate the effect of the treatment on the sensory properties of the product. A 1-kGy dose of E-beam radiation reduced E. coli O157:H7 inoculated onto sections of cutaneous trunci at least 4 log CFU/cm2. In assessing organoleptic impact, flank steak was used as the model muscle. Flank steaks with various levels of penetration by radiation (5, 10, 25, 50, and 75%) were evaluated. None of the flank steak sensory attributes were affected (P > 0.05) by any penetration treatment. Ground beef formulations consisting of 100, 50, 25, 10, 5, and 0% surface-irradiated beef were tested. A trained sensory panel did not detect any difference between the control (0%) and either the 5 or 10% treatments. These results suggest that if chilled carcasses were subjected to low-dose E-beam irradiation, aroma and flavor of ground beef would not be impacted. The data presented here indicate that low-dose, low-penetration E-beam irradiation has potential use as an antimicrobial intervention on beef carcasses during processing and minimally impacts the organoleptic qualities of the treated beef products.