Water reconditioning by high power ultrasound combined with residual chemical sanitizers to inactivate foodborne pathogens associated with fresh-cut products

The suitability of high power ultrasound (HPU, 20 kHz, 0.28 kW/l) combined with residual chemical sanitizers for water reconditioning was studied. A synergetic disinfection effect was observed when HPU was combined with peroxyacetic acid (PAA) or a commercial mix of organic acids and phenolic compounds (OA/PC). In recycled water (RW) with a chemical oxygen demand (COD) of 500 mg O₂/l, PAA inactivated 2 log units of Escherichia coli O157:H7 at concentrations of 3.2, 6.4, 16 mg/l after 7 min, 2 min, 29 s, respectively. The OA/PC or HPU treatments alone needed 26 min treatments to achieve the same reduction. The addition of TiO₂ (5 g/l) to HPU (sonocatalysis) did not improve E. coli O157:H7 inactivation. However, when HPU was combined with a residual concentration of PAA (3.2 mg/l), the total inactivation of E. coli O157:H7 and Salmonella (6 log unit reductions) occurred after 11 min, but for Listeria monocytogenes only 1.7 log reductions were detected after 20 min. When HPU was combined with OA/PC, a synergistic effect for the inactivation of E. coli O157:H7 was also observed, but this sanitizer significantly modified the physical-chemical quality characteristics of the RW. These results show that the residual PAA concentration that can be found in the wash water combined with HPU could result in an environmentally friendlier and toxicologically safer strategy for water reconditioning of the fresh-cut industry. The use of the sanitizer alone requires higher concentrations and/or longer contacts times. Even though the residual PAA in combination with HPU was adequate for water reconditioning, it is not appropriate for the process wash water because this wash water must be instantaneously disinfected.     

Inactivation of Escherichia coli O157:H7 in vitro and on the surface of spinach leaves by biobased antimicrobial surfactants

This study was conducted to evaluate the effect of biosurfactants on the populations of Escherichia coli O157:H7 in suspension and on spinach leaves. Eight surfactants including four soybean oil-based biosurfactants, sodium dodecyl sulfate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), sophorolipid (SO) and thiamine dilauryl sulfate (TDS) at concentrations of 0.1%, 0.5% and 1.0% were tested in bacterial suspension, and the most effective biosurfactants were applied on spinach leaves. Results showed that the soybean oil-based biosurfactants, SDS or Tween 80 did not significantly affect E. coli O157:H7 populations. SO and TDS at concentrations of 1.0% were effective in reducing E. coli O157:H7 populations in bacterial suspension. E. coli O157:H7 with an initial population of 7.1 log CFU/mL was not detectable (detection limit: 1 log CFU/mL) after 1 min in 1.0% TDS or after 2 h in 1.0% SO. On spinach leaves, SO at 1% did not significantly affect E. coli when compared to a water wash during 7 days post-treatment storage at 4 °C. However, TDS (1.0%) wash was as effective as 200 ppm chlorine in reducing population of spot inoculated E. coli O157:H7, achieving 3.1 and 2.7 log CFU/per leaf at day 0, and 1.4 and 1.9 log CFU/leaf at day 7 when compared with a water wash. No apparent change in spinach visual quality was observed. None of treatments caused changes in visual quality of spinach. Electron micrographs suggested ultrastructural damage of bacterial cells such as separation of the outer membrane from the cytoplasmic membrane. Overall, our results showed that SO and TDS may be potential sanitizers in inactivating human pathogens such as E. coli O157:H7 in wash water and on fresh produce.     

Effects of organic load,sanitizer pH and initial chlorine concentration of chlorine-based sanitizers on chlorine demand of fresh produce wash waters

Chlorine-based sanitizers are widely used in fresh produce industry. However, maintaining sufficient free chlorine residual in wash solution in the presence of organic matter is a challenge. The purpose of this study was to evaluate the effects of organic load, sanitizer pH and initial chlorine concentration on chlorine demand of fresh produce wash water. A full factorial design was used to study the chlorine demand of romaine lettuce wash water with different organic load when reacting with NaOCl solution at different pH (2.5, 4.0, 6.0, 8.0 and 9.5) and initial chlorine concentration (50, 75 and 100 mg L⁻¹ free chlorine residual). The results showed that the chlorine demand of lettuce wash water significantly increased (P ≤ 0.05) with increasing organic load. The significant effect (P ≤ 0.05) of initial chlorine concentration on chlorine demand was only detected at high organic load. Increasing the pH of NaOCl from 2.5 to 9.5 led to decrease in the chlorine demand except slight increase from 6.0 to 8.0. Equations for predicting chlorine demand of various fresh produce wash waters at different organic load for different sanitizer pH and initial chlorine concentration were developed, and verified using four types of produce (romaine lettuce, iceberg lettuce, strawberry and grape) and two types of chlorine-based sanitizers (NaOCl and electrolyzed water). Our study demonstrated that organic load, sanitizer pH and initial chlorine concentration all affected the chlorine demand of produce wash water, and chlorine demand prediction equations developed can be used for different types of fresh produce and chlorine-based sanitizers.     

Inactivation effect of newly developed low concentration electrolyzed water and other sanitizers against microorganisms on spinach

The efficacy of newly developed low concentration electrolyzed water (LcEW) was investigated to inactivate the pathogens on spinach leaves as a convenient and safe alternative sanitizer and it was compared to other sanitizers. Spinach leaves were inoculated with Escherichia coli O157:H7 and Listeria monocytogenes and dip treated with deionized water (DIW), LcEW, strong acid electrolyzed water (SAEW), aqueous ozone (AO), 1% citric acid (CA) and sodium hypochlorite solution (NaOCl) for 3 min at room temperature (23 ± 2 °C). For all pathogens, the similar pattern of microbial reduction on spinach was apparent with LcEW and SAEW washing. In the present study, it was found that LcEW inactivated, at maximum, 1.64–2.80 log cfu/g and DIW resulted in lowest reduction, 0.31–0.95 log cfu/g of background or pathogenic microflora present on spinach leaves compared to the unwashed control. The findings of this study indicate that LcEW and SAEW did not differ significantly (P > 0.05) in reducing background or pathogenic microflora on spinach and LcEW may be a promising sanitizer for washing vegetables without environmental pollution instead of using electrolyzed oxidizing (EO) water or SAEW.     

Comparative efficacies of various chemical sanitizers for warewashing operations in restaurants

This study compared the efficacies of two traditional with two experimental sanitizers for use in tableware cleaning operations in restaurants and foodservice operations. This was done by investigating the maximum number of cleaning cycles that a single recommended quantity of each sanitizer could treat and still produce a 5-log bacterial reduction on test tableware items. Cream cheese and whole milk were inoculated with Escherichia coli K12 and Listeria innocua and subsequently used for contamination of the tableware items. These items were washed with automatic (49 °C) and manual (43 °C) dishwashers then treated with electrolyzed-oxidizing water (EO), quaternary ammonium compound, sodium hypochlorite and an acidic sanitizer. For the lowest efficacies, after six and eight manual washing cycles in the same solution, ≥5 log reductions were achieved on both E. coli K12 contaminated trays and plates, respectively, exposed to the chlorine and quaternary ammonium sanitizers. For automatic washing with chlorine sanitizer, the minimum wash cycles for the bacteria were seven and nine for the trays and plates, respectively. For drinking glasses contaminated with bacteria, 14 and 17 washing cycles produced ≥5 log reductions for manual and automatic washings, respectively.     

Efficacy of sanitizers in reducing Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes populations on fresh-cut carrots

Shredded carrots were inoculated with Escherichia coli O157:H7, Salmonella or Listeria monocytogenes and washed for 1 or 2 min with chlorine (Cl; 200 ppm), peroxyacetic acid (PA; 40 ppm) or acidified sodium chlorite (ASC; 100, 200, 500 ppm) under simulated commercial processing conditions. After washed, the carrots were spin dried, packaged and stored at 5 °C for up to 10 days. Bacterial enumeration was significantly (P ⩽ 0.05) reduced by 1, 1.5 and 2.5 log CFU/g after washing with ASC 100, 250 and 500 ppm, respectively. All sanitizers reduced pathogen load below that of tap water wash and unwashed controls. During storage at 5 °C the bacterial load of all treatments increased gradually, but to different extent in different treatments. ASC inhibited bacterial growth more effectively than the other sanitizers and also maintained the lowest pathogen counts (<1 log CFU/g) during storage. Organic matter in the process water significantly (P ⩽ 0.05) reduced the antibacterial efficacy of Cl, but not that of PA or ASC. Therefore, ASC shows the potential to be used as a commercial sanitizer for washing shredded carrots.     

The efficacy of chemical sanitizers on the reduction of Salmonella Typhimurium and Escherichia coli affected by bacterial cell history and water quality

Washing fresh produce with potable water helps to remove microorganisms, providing about a 1- to 2-log reduction, but this process can also pose an opportunity for cross-contamination of bacteria in the washing tank. The objective of this study was to evaluate the efficacy of three chemical sanitizers, sodium hypochlorite, chlorine dioxide, and a silver-copper solution on the reduction of S. Typhimurium and extended-spectrum beta-lactamase (ESBL) E. coli as well as to evaluate the impact bacterial cell history and water quality had on sanitizer efficacy. This was investigated with three scenarios representing different contamination routes and history of cells: (i) on starved and non-starved cells in potable water, (ii) on starved and non-starved cells in lettuce wash water and on lettuce leaf punches, and (iii) on non-starved cells in organically loaded process wash water (PWW). Sodium hypochlorite (NaClO) and chlorine dioxide (ClO₂) were more effective in preventing cross-contamination in the potable water than the silver-copper solution. Starved and non-starved bacterial cells displayed minor differences in their susceptibility to sanitizing agents in the (i) potable water and (ii) lettuce wash water demonstrating that other conditions greater influenced sanitizer efficacy. Particularly, the organic load of the water, wash water temperature, and pathogen attachment and release from the produce were shown to affect a sanitizer's efficacy during washing. Furthermore, results emphasize that chemical sanitizer use should focus more on wash water disinfection, rather than produce decontamination, to prevent pathogenic cross-contamination during processing. Future research should investigate the feasibility of ClO₂ application during pilot-scale processing.     

Microbiological quality of fresh vegetables and fruits sold in Singapore

The aim of this study was to characterise the microbiological quality of selected common fresh vegetables and fruits commercially sold in Singapore in order to provide insight into any potential health hazards associated with consumption of these commodities. A total of 125 samples, collected from major supermarkets and local markets, were tested for aerobic mesophilic and psychrotrophic bacterial counts. One hundred samples were analysed for enumeration of yeasts and moulds, enumeration of coliforms and detection of Escherichia coli O157:H7 and Salmonella spp. Aerobic mesophilic counts ranged from 1.6 to 9.1 log cfu/g, with the lowest and the highest counts recorded for orange and bean sprouts, respectively. The highest level of coliforms was found in bean sprouts and fresh-cut salad, with 50% of samples containing more than 5 log cfu/g. Like coliform counts, the highest counts of yeasts and moulds were obtained in bean sprouts and fresh-cut salads. Fresh-cut salads also had the highest mean psychrotrophic plate count of 4.9 log cfu/g. Although no E. coli O157:H7 or Salmonella spp. was detected in the fruits and vegetables analysed in this study, high bacterial counts, especially in bean sprouts and fresh-cut salad, imply that effective control measures should be implemented to improve the microbiological quality of fresh produce sold in Singapore.     

Effects of spray volume, type of surface tissue and inoculum level on the survival of Escherichia coli on beef sprayed with 5% lactic acid

Membrane, fat and cut muscle surfaces of beef were inoculated with Escherichia coli at numbers about 4, 1 or −1 log cfu/cm². The inoculated meat was sprayed with water or 5% lactic acid at volumes of 0.5, 0.1 or 0.02 ml/cm². Spraying with water reduced the numbers of E. coli on membrane surfaces by up to 1 log unit, but had little effect on the numbers of E. coli on fat or cut muscle surfaces. Spraying with 5% lactic acid reduced the highest numbers of E. coli on membrane surfaces by up to 4 log units; but those numbers on fat or cut muscle surfaces were reduced by ≤1.5 log unit, and the reductions declined with decreasing volumes of 5% lactic acid. With inocula of 1 log cfu/cm², spraying lactic acid in any volume reduced the numbers of E. coli on membrane or fat surfaces by about 1 log unit, and the numbers on cut muscle surfaces by between 0.8 and 0.2 log unit. E. coli were detected in enrichment cultures of samples from all surfaces inoculated with E. coli at −1 log cfu/cm² and sprayed with 5% lactic acid at 0.5 ml/cm². The findings indicate that spraying relatively heavily contaminated cuts or trimmings with 5% lactic acid at ≥0.1 ml/cm² can be expected to reduce numbers of E. coli and, presumably, associated pathogens by between 0.5 and 1 log unit. However, such a treatment is likely to be at best marginally effective for reduce the numbers of these organisms on lightly contaminated product.     

A novel electrochemical device as a disinfection system to maintain water quality during washing of ready to eat fresh produce

Electrolyzed water (EW) is known by its bactericidal efficacy and capability to oxidize organic matter. The present research evaluated the efficacy of recently developed electrolytic cells able to generate higher concentration of reactive oxygen species using lower power and salt concentration than conventional cells. This study tested the inactivation of Escherichia coli O157:H7, the organic matter depletion and trihalomethane (THM) generation by EW in process wash water under dynamic conditions. To achieve this, clean tap water was continuously added up to 60 min with artificial process water with high chemical oxygen demand (COD) inoculated with E. coli O157:H7, in experiments performed in a pilot plant that recirculated water through one electrolytic cell. Plate counts of E. coli O157:H7, COD, THMs, free, combined and total chlorine, pH, temperature and oxidation-reduction potential were determined. Results indicate that the novel electrolysis system combined with minimal addition of NaCl (0.05%) was able to suppress E. coli O157:H7 population build-up and decreased the COD accumulation in the process wash water. THM levels in the water were relatively high but its concentration in the washed product was marginal. Highly effective electrolysis has been proven to reduce the occurrence of foodborne diseases associated to cross-contamination in produce washers without having an accumulation of THMs in the washed product.     

Good agricultural practices in a Brazilian produce plant

A Brazilian produce plant was evaluated according to good agricultural practices (GAPs) using a checklist. The agricultural water was sampled for total and faecal coliform and Escherichia coli counts. Equipment/handler sanitary facilities, the handling of agrochemicals and pesticides, records of the composting process, prior analysis of the irrigation water for the identification of heavy metals and pesticide residues, inadequate temperature control of the raw material storage room, qualified person to manage the operations and periodic training programmes on food manipulation, hygiene and microbiology, were the main critical points found during the inspection. Microbiological analyses of the irrigation water gave counts between 0.3 and 1.2 log MPN/ml for total and faecal coliforms, respectively and absence of E. coli. The results are discussed and the necessary corrections suggested in order to improve process safety.     

Development of a novel economical device to improve post-harvest processing practices on small farms

Consumer demand for fresh produce has increased; however, multiple microbial foodborne outbreaks in the past decade have involved fresh leafy greens. While large farms may process their own leafy greens or use an external processor that uses aqueous sanitizers, small farms may not have these options. Hence, it is important to equip small farmers with simple and effective methods to reduce on-farm pathogen contamination. The goal of this study was to develop a novel device that can improve post-harvest practices on small farms growing leafy greens. A survey was administered to identify farmers' concerns associated with the post-harvest phase of production. The results indicated that most farmers do not wash leafy greens in a sanitizing solution, but would like information on how to improve the safety of their produce. As a result of this survey, a novel sanitizing device was developed to wash, sanitize (with diluted white vinegar containing acetic acid (AA)), and dry leafy greens. The result showed that 1.6% AA for 2 min was effective against coliforms, yeast, mold, and pathogenic surrogates (Listeria, Salmonella, and Escherichia coli). Significant reduction of aerobic bacteria and coliforms were observed at 2.5% AA for 2 min and 1.6% for 2 min treatment at 3 log CFU/g and 2.28 log CFU/g respectively. The use of this device may help farmers wash and sanitize fresh leafy greens effectively, reduce the risk of foodborne pathogen contamination, and improve produce shelf-life.     

Microbiological contamination linked to implementation of good agricultural practices in the production of organic lettuce in Southern Brazil

Interviews were conducted with the owners of three organic lettuce farms in the state of Rio Grande do Sul in southern Brazil using a standardized self-assessment questionnaire to ascertain the status of implementation of good agricultural practices and management systems in place. In addition, on each farm 132 samples (manure, field soil, water, workers' hands and equipment, lettuce seedlings, and crops) were collected during four visits throughout the lettuce crop production cycle and subjected to analysis for hygiene indicators (Escherichia coli, coliforms) and presence of Salmonella and E. coli O157. E. coli O157 was detected twice (in irrigation water and in rinse water) out of 27 analyzed water samples. Salmonella spp. was detected in one out of nine manure samples applied as organic fertilizer. In addition, generic E. coli was frequently present in numbers exceeding 10 cfu/g in manure, manured soil, and lettuce samples or more than 1 cfu/100 ml in water. No E. coli O157 was detected in any of the lettuce samples (n = 36), but Salmonella spp. was detected once in lettuce taken during the crop cycle 2 weeks before harvest. It was demonstrated that the combination of the self-assessment questionnaire and microbiological sampling and analysis could identify weak points in current organic farming practices in this region of southern Brazil. It was noted that manure composting was not adequately controlled and appropriate waiting times before application as an organic fertilizer to crop were not respected. Also the selection of the water source and the sanitary quality of the water used for irrigation were not under control. The washing step (with sanitizer) of lettuce crops at harvest, generally considered a potential reduction step for microbial contamination, was often not verified for its efficiency. This may detract from the sanitary quality of the produce and are risk factors for the introduction of pathogens in the lettuce sent to market. The study, combining interviews, sampling, and analysis, contributed to increasing the farmers' awareness of enteric pathogens as a food safety issue in leafy greens. Further communication and training on good agricultural practices are recommended to remediate the weak points identified in the current management system.     

Effect of organic acids,hydrogen peroxide and mild heat on inactivation of Escherichia coli O157:H7 on baby spinach

Minimally processed baby spinach contaminated with Escherichia coli O157:H7 has been associated with multiple outbreaks of foodborne illnesses recently. Chlorinated water is widely used to wash vegetables commercially, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. This study was conducted to determine the effects of organic acids and hydrogen peroxide alone and in binary combinations with or without mild heat (40 and 50 °C) on the inactivation of Escherichia coli O157:H7 on baby spinach. Baby spinach leaves were dip-inoculated with E. coli O157:H7 to a level of 6 log CFU/g and stored at 4 °C for 24 h before treatment. Individual washing solutions (1% and 2% lactic acid [LA], citric acid [CA], malic acid [MA], tartaric acid [TA], acetic acid [AA], hydrogen peroxide [H₂O₂] as well as binary combinations of LA, CA, MA and H₂O₂ at final concentrations of 1% were used to decontaminate spinach leaves at 22, 40 or 50 °C for 2–5 min to test their efficacy in reducing E. coli O157:H7. Chlorinated water (200 ppm free chlorine) decreased the population of E. coli O157:H7 on baby spinach by only 1.2–1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% LA at 40 °C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7 which is significantly higher than chlorine washing. Washing with LA + CA or LA + HP at 40 °C for 5 min was equally effective against E. coli O157:H7, resulting in a 2.7 log reduction of E. coli O157:H7. The application of mild heat significantly enhanced the efficacy of washing solutions on the inactivation of E. coli O157:H7. There was, however, no significant difference between treatments at 40 °C for 5 min and 50 °C for 2 min. The results suggested that the use of organic acids in combination with mild heat can be a potential intervention to control E. coli O157:H7 on spinach.     

Modeling the growth rates of Escherichia coli spp. and Salmonella Typhimurium LT2 in baby spinach leaves under slow cooling

After field harvest, baby spinaches are transported to the packing shed where they are cooled by forced air systems. If contaminated, the temperature of spinaches will affect the number of pathogens in the leaves, and effective temperature control is critical to restrict their growth. Hence, the need to assess the impact of cooling practices on the growth of pathogens in leafy greens. The Baranyi model was used to describe the experimental data and build a dynamic model to predict microorganism growth rate in baby spinach leaves as function of temperature.Baby spinach leaves, inoculated with 10⁴ CFU/ml of Salmonella Typhimurium LT2 or 10² CFU/ml of an Escherichia coli cocktail, and were maintained at temperatures ranging from 10 to 37 °C for 30 h. At 10–30 °C, the E. coli strains grew significantly more (～2–4 log cycles) than the Salmonella strain (～0.11–2.4 log cycles) while at 37 °C, both bacterial populations increased by ～6 log cycles for 30 h. The growth kinetics of each microorganism followed the Baranyi model. The maximum bacterial population increased with temperature and the values were similar for both bacteria. The theoretical minimum temperature for growth was 5.88 °C and 4.76 °C for Salmonella and E. coli, respectively. The dynamic model was validated with an experimental linear cooling profile (slow cooling) and could be incorporated into a risk assessment tool to evaluate the growth of pathogens in baby spinach during processing and distribution.     

Hygienic quality of head lettuce: Effects of organic and mineral fertilizers

The hygienic quality of head lettuce (Lactuca sativa L.) was investigated after different fertilizer treatments (fresh farmyard manure, composted farmyard manure, stinging nettle extract and calcium ammonium nitrate) in a 2-year field experiment with two trials per year, respectively. For assessment of the hygienic quality the total aerobic bacterial counts, Enterobacteriaceae, coliform bacteria, Escherichia coli and Salmonella were investigated in soil, fertilizer and lettuce samples. Plants were washed with running tap water before analysis. The total aerobic bacterial count, as well as the levels of Enterobacteriaceae and coliform bacteria tended to be slightly higher (not significant) after organic compared to mineral fertilization. No Salmonella was detected in any soil, fertilizer or lettuce sample, while E. coli was randomly detected in low concentrations independent from fertilizer treatment. No higher risk of bacterial contamination due to the use of organic fertilizers was indicated.     

Potential of Escherichia coli as a surrogate indicator for postchill broiler carcasses with high Campylobacter counts

Surrogating Campylobacter contamination level in broiler carcasses with other bacterial indicators, used to evaluate the hygienic status of the slaughterline operations, might be stimulation to the broiler meat industry to improve control of Campylobacter during slaughter. Theoretically, Escherichia coli might have some practical merits as a potential indicator for carcasses contaminated with Campylobacter. This study investigates the correlation between the counts of E. coli and Campylobacter in 231 postchill broiler carcasses. The impact of setting a process hygiene target based on E. coli counts on reducing the frequency of carcasses contaminated with Campylobacter at level of ≥3 log₁₀ CFU/g was also investigated. Almost half (48.9% (46/94)) of the carcasses with enumerable Campylobacter (≥1 log₁₀ CFU/g) had E. coli counts between 3 and 4 log₁₀ CFU/g. In addition, 54.8% (17/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g were correlated with E. coli count range of ≥3 & <4 log₁₀ CFU/g. A theoretical scenario assuming that hygiene and processing measures could allow achieving a target for E. coli that not exceeding 3 log₁₀ CFU/g showed a parallel impact on Campylobacter contamination in broiler carcasses. In such scenario, the overall number of Campylobacter-positive carcasses could be dropped from 40.6% to 12.5%; in addition, 80.6% (25/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g could be eliminated. Findings from this study reveal that a hygiene target based on E. coli count could be used as an indirect sanitary tool for reducing the level of Campylobacter contamination in postchill broiler carcasses.     

Removal of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 biofilms on stainless steel using scallop shell powder

Biofilms on steel surfaces containing Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 continue to threaten dairy and meat processors. In this study, the ability of scallop shell powder (SSP) to remove biofilms formed by these three pathogens on stainless steel plates was examined. Whey powder solution (WPS) and bench wash water (BWW) provided by dairy and meat factories, respectively, were inoculated with L. monocytogenes, S. aureus or E. coli O157:H7 (9 log₁₀ CFU/ml). Stainless steel plates (10 cm²) were placed in the inoculated fluids and incubated at 20 °C at 48 h to form biofilms. After drying and washing in sterile water, the plates were treated with 0.0, 0.25, or 0.50% (w/v) SSP slurries for 1, 5, or 10 min and then quantitatively examined for the three pathogens. Both 0.25 and 0.50% SSP reduced L. monocytogenes on the plates by 4 log CFU/cm² with a 1 min exposure to 0.50% SSP decreasing S. aureus by 5 logs CFU/cm². After 1 min in 0.25 and 0.50% SSP, E. coli O157:H7 populations in WPS and BWW biofilms decreased 4 and 6 log CFU/cm² and 3 and 5 log CFU/cm², respectively. Increasing the concentration of SSP led to significantly increased efficacy against the tested pathogens (P < 0.05). In conclusion, this study showed that SSP slurries could significantly reduce the numbers of L. monocytogenes, S. aureus and E. coli O157:H7 in biofilms on stainless steel surfaces.     

Efficacy of pulsed electric fields for the inactivation of indicator microorganisms and foodborne pathogens in liquids and raw chicken

This study investigated the ability of pulsed electric fields (PEF) to inactivate a range of microorganisms in liquid media and on raw chicken meat. The susceptibilities of ten Campylobacter isolates (seven Campylobacter jejuni isolates and three Campylobacter coli isolates), Escherichia coli (ATCC 25922) and Salmonella Enteritidis (ATCC 13076) to PEF in liquid media were investigated. All Campylobacter isolates tested in liquid were susceptible to PEF treatment (65 kV/cm, 5 μs, 500 Hz) with reductions of between 4.33 and 7.22 log₁₀ CFU/mL observed for the longest treatment (30 s). Significant differences in susceptibility were observed between Campylobacter isolates subjected to equivalent PEF treatments ranging from 2.41 to 5.19 log₁₀ CFU/mL. Campylobacter isolates processed in liquid media were found to be more sensitive to PEF than E. coli and S. Enteritidis (P < 0.05). The application of PEF (3.75 and 15 kV/cm, 10 μs, 5 Hz) to inoculated samples of raw chicken did not result in any significant reductions in total viable counts, Enterobacteriaceae, C. jejuni, E. coli or S. Enteritidis. Therefore, under the conditions used in this study, PEF technology may not be suitable as a food safety intervention measure for the control of microbial contaminants on broilers during processing although it may have potential to reduce contamination of process water (e.g. scald or spin chill water).     

A Turkey survey of hygiene indicator bacteria and Yersinia enterocolitica in raw milk and cheese samples

In this research, a total of 200 dairy (raw milk, cheese) samples obtained from Ankara, were examined for the presence of Yersinia spp., total coliform and Escherichia coli. As expected, raw milk 55% (55/100) were significantly contaminated with Yersinia spp., than cheese samples 14% (14/100). Y. enterocolitica was the most commonly isolated species, and was recovered from 47.3% in raw milk 35.7% in cheese samples. The other Yersinia spp. were identified as Y. frederiksenii (31.0%, 21.4%), Y. kristensenii (12.7%), Y. intermedia (7.2%, 7.1%) and atypical Yersinia spp. (1.8%, 35.7%) in raw milk and cheese samples, respectively. All the samples of cheese examined were negative for Y. kristensenii. All Y. enterocolitica strains tested gave negative results in the autoagglutination tests and crystal violet binding test.Furthermore total coliform bacteria and E. coli were investigated in these samples. According to the analysis results, most of the samples containing Yersinia spp.were found high number of viable count cell total coliform than E. coli. Total coliform bacteria and E. coli, were detected (3.0 × 10⁴ cfu/ml and 1.5 × 10⁴ cfu/ml) in four milk samples containing Y. enterocolitica while, they were detected (2.5 × 10⁴ cfu/ml and 1.0 × 10⁴ cfu/ml) in eight milk samples containing Y. enterocolitica. In the present study, total coliform bacteria and E. coli were detected >1.1 × 10⁵ cfu/g in six cheese samples containing Y. enterocolitica and atypical Yersinia spp. The results indicate that Yersinia spp. is more likely to be isolated from foods with a high level of coliforms than from foods with low coliform counts.