Control of foodborne pathogens on fresh-cut fruit by a novel strain of Pseudomonas graminis

The consumption of fresh-cut fruit has substantially risen over the last few years, leading to an increase in the number of outbreaks associated with fruit. Moreover, consumers are currently demanding wholesome, fresh-like, safe foods without added chemicals. As a response, the aim of this study was to determine if the naturally occurring microorganisms on fruit are “competitive with” or “antagonistic to” potentially encountered pathogens. Of the 97 and 107 isolates tested by co-inoculation with Escherichia coli O157:H7, Salmonella and Listeria innocua on fresh-cut apple and peach, respectively, and stored at 20 °C, seven showed a strong antagonistic capacity (more than 1-log unit reduction). One of the isolates, CPA-7, achieved the best reduction values (from 2.8 to 5.9-log units) and was the only isolate able to inhibit E. coli O157:H7 at refrigeration temperatures on both fruits. Therefore, CPA-7 was selected for further assays. Dose-response assays showed that CPA-7 should be present in at least the same amount as the pathogen to adequately reduce the numbers of the pathogen. From the results obtained in in vitro assays, competition seemed to be CPA-7's mode of action against E. coli O157:H7. The CPA-7 strain was identified as Pseudomonas graminis. Thus, the results support the potential use of CPA-7 as a bioprotective agent against foodborne pathogens in minimally processed fruit.     

Fate of Escherichia coli O157:H7, Salmonella and Listeria innocua on minimally-processed peaches under different storage conditions

Consumption of fresh-cut produce has sharply increased recently causing an increase of foodborne illnesses associated with these products. As generally, acidic fruits are considered ‘safe’ from a microbiological point of view, the aim of this work was to study the growth and survival of Escherichia coli O157:H7, Salmonella and Listeria innocua on minimally-processed peaches. The three foodborne pathogens population increased more than 2 log₁₀ units on fresh-cut peach when stored at 20 and 25 °C after 48 h. At 10 °C only L. innocua grew more than 1 log₁₀ unit and it was the only pathogen able to grow at 5 °C. Differences in growth occurred between different peach varieties tested, with higher population increases in those varieties with higher pH (‘Royal Glory’ 4.73 ± 0.25 and ‘Diana’ 4.12 ± 0.18). The use of common strategies on extending shelf life of fresh-cut produce, as modified atmosphere packaging and the use of the antioxidant substance, ascorbic acid (2% w/v), did not affect pathogens’ growth at any of the temperatures tested (5 and 25 °C). Minimally-processed peaches have shown to be a good substrate for foodborne pathogens’ growth regardless use of modified atmosphere and ascorbic acid. Therefore, maintaining cold chain and avoiding contamination is highly necessary.     

Comparative study of improved vs. traditional apple cultivars and their aptitude to be minimally processed as ‘ready to eat’ apple wedges

The development of fresh-cut apple products requires the reconsideration of cultivar selection because different characteristics are required compared with those characteristics for the fresh market. The aim of this work was to evaluate four improved cultivars (‘Modì’, ‘Ariane’, ‘Fuji Kiku 8’ and ‘Pink Lady’) and to compare these cultivars with traditional cultivars (‘Golden Smoothee’ and ‘Granny Smith’). Cultivars were evaluated according to physicochemical parameters and nutritional, enzymatic, and sensory aspects. Next, the cultivars were peeled, cut, treated with different antioxidant treatments, packaged in polypropylene trays and stored at 4 °C. After seven days of storage, physicochemical parameters and visual assessment were determined. As whole apples, the improved cultivars were notable for their sensory characteristics. Moreover, two of them (‘Modì’ and ‘Ariane’) presented the highest amount of total phenols and vitamin C, respectively. After processing and storage, certain of the improved cultivars presented better aptitude for minimal processing. For instance, ‘Modì’ showed high suitability, and ‘Fuji Kiku 8’ was notable for its sensory quality after seven days of refrigerated storage. Among antioxidant treatments that were assayed, 40 g/L NatureSeal^® demonstrated the best results in terms of physicochemical parameters, visual assessment and sensory quality.     

Effects of packaging type and storage temperature on the growth of foodborne pathogens on shredded ‘Romaine’ lettuce

Fresh produce can be a vehicle for the transmission of pathogens capable of causing human illnesses and some of them can grow on fresh-cut vegetables. The survival and growth of Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes inoculated onto shredded lettuce was determined under modified atmosphere packaging conditions, at various storage temperatures. We also monitored changes in pH and gas atmospheres within the packages and the growth of psychrotrophic and mesophilic microorganisms. After pathogen inoculation, shredded lettuce was packaged in films of different permeability and stored at 5 and 25 °C. After 10 days at 5 °C populations of E. coli O157:H7 and Salmonella decreased approximately 1.00 log unit while L. monocytogenes increased about 1.00 log unit, in all package films. Moreover, the pathogens level increased between 2.44 and 4.19 log units after 3 days at 25 °C. Psychrotrophic and mesophilic bacteria had similar growth at both temperatures with higher populations in air than in the other atmospheres. The composition of the storage atmosphere within the packaging of lettuce had no significant effect on the survival and growth of the pathogens used in this study at refrigeration temperatures. The results obtained can be considered as a warning indicator, which reinforces the necessity for corrective measures to avoid contamination of vegetables.     

Antagonistic effect of Pseudomonas graminis CPA-7 against foodborne pathogens in fresh-cut apples under simulated commercial conditions

Recently, we reported that the application of the strain CPA-7 of Pseudomonas graminis, previously isolated from apple, could reduce the population of foodborne pathogens on minimally processed (MP) apples and peaches under laboratory conditions. Therefore, the objective of the present work was to find an antioxidant treatment and a packaging atmosphere condition to improve CPA-7 efficacy in reducing a cocktail of four Salmonella and five Listeria monocytogenes strains on MP apples under simulated commercial processing. The effect of CPA-7 application on apple quality and its survival to simulated gastric stress were also evaluated. Ascorbic acid (2%, w/v) and N-acetyl-l-cysteine (1%, w/v) as antioxidant treatments reduced Salmonella, L. monocytogenes and CPA-7 recovery, meanwhile no reduction was observed with NatureSeal^® AS1 (NS, 6%, w/v). The antagonistic strain was effective on NS-treated apple wedges stored at 10 °C with or without modified atmosphere packaging (MAP). Then, in a semi-commercial assay, efficacy of CPA-7 inoculated at 10⁵ and 10⁷ cfu mL⁻¹ against Salmonella and L. monocytogenes strains on MP apples with NS and MAP and stored at 5 and 10 °C was evaluated. Although high CPA-7 concentrations/populations avoided Salmonella growth at 10 °C and lowered L. monocytogenes population increases were observed at both temperatures, the effect was not instantaneous. No effect on apple quality was detected and CPA-7 did not survived to simulated gastric stress throughout storage. Therefore, CPA-7 could avoid pathogens growth on MP apples during storage when use as part of a hurdle technology in combination with disinfection techniques, low storage temperature and MAP.     

Transfer of Listeria innocua from contaminated compost and irrigation water to lettuce leaves

Many foodborne outbreaks of some pathogens such as Escherichia coli O157:H7, Salmonella or Listeria have been associated with the consumption of contaminated vegetables. Contaminated manure and polluted irrigation water are probable vehicles for the pathogens. The aim of this study was to determine the potential transfer of Listeria innocua from soil fertilized with contaminated compost or irrigated with contaminated water to the edible parts of lettuce grown on these soils together with its survival in lettuce and in soil under field conditions during two different seasons. Moreover, its survival on lettuce sprinkled with contaminated irrigation water was evaluated. L. innocua survived in soil samples for 9 weeks at high concentrations, 10⁵ cfu gdw⁻¹ in fall and 10³ cfu gdw⁻¹ in spring. Pathogen survived better in fall, indicating an important influence of temperature and humidity. L. innocua population in lettuce leaves was very high on lettuce leaves after sprinkling, but decreased to undetectable levels at field conditions. There was also transfer of L. innocua from soil contaminated with compost or irrigated with contaminated water to lettuce leaves, mainly to the outer ones. Survival profiles of L. innocua on lettuce and soil samples contaminated either by application of contaminated compost or surface irrigation water was similar. Our results indicated that contaminated compost and contaminated irrigation water can play an important role in the presence of foodborne pathogens on vegetables.     

Inactivation of Salmonella and Escherichia coli O157:H7 on artificially contaminated alfalfa seeds using high hydrostatic pressure

Alfalfa sprouts contaminated with Salmonella and Escherichia coli O157:H7 have been implicated in several outbreaks of foodborne illnesses in recent years. The seed used for sprouting appears to be the primary source of pathogens. Seed decontamination prior to sprouting presents a unique challenge for the sprouting industry since cells of the pathogenic survivors although undetectable after sanitizing treatments, can potentially multiply back to hazardous levels. The focus of this study was to therefore test the efficacy of high hydrostatic pressure to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Pressure treatment of 600 MPa for up to 25 min at 20 °C could not result in complete inactivation of Salmonella. High-pressure treatment was then carried out either at sub-ambient (4 °C) or elevated (40, 45 and 50 °C) temperatures to test the ability of high pressure to eliminate Salmonella. Pressure treatment at 4 and 20 °C did not deliver any satisfactory inactivation of Salmonella while high pressure at elevated temperatures achieved complete kill. Pre-soaking seeds prior to high-pressure treatment also enhanced pressure inactivation of Salmonella but at the expense of seed viability. High-pressure treatment of 500 MPa for 2 min at 45 °C was able to eliminate wild-type Salmonella and E. coli O157:H7 strains without bringing about any appreciable decrease in the seed viability.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Comparative efficacy of Zataria multiflora Boiss., Origanum compactum and Eugenia caryophyllus essential oils against E. coli O157:H7, feline calicivirus and endogenous microbiota in commercial baby-leaf salads

Ready-to-eat salads using baby-leaf and multi-leaf mixes are one of the most promising developments in the fresh-cut food industry. There is great interest in developing novel decontamination treatments, which are both safe for consumers and more efficient against foodborne pathogens. In this study, emulsions of essential oils (EOs) from Origanum compactum (oregano), Eugenia caryophyllus (clove), and Zataria multiflora Boiss (zataria) were applied by spray (0.8 ml) after the sanitizing washing step. The aim was to investigate their ability to control the growth of potentially cross-contaminating pathogens and endogenous microbiota in commercial baby leaves, processed in a fresh-cut produce company. Zataria EO emulsions of 3%, 5% and 10% reduced Escherichia coli O157:H7 by 1.7, 2.2 and 3.5 log cfu/g in baby-leaf salads after 5 days of storage at 7 °C. By contrast, reductions in E. coli O157:H7 counts remained the same when clove was applied at concentrations of 5% and 10% (2.5 log cfu/g reduction). Oregano (10%) reduced inoculated E. coli O157:H7 counts in baby-leaf salads by a maximum of 0.5 log cfu/g after 5 days of storage. Zataria showed strong antimicrobial efficacy against E. coli O157:H7 and also against the endogenous microbiota of baby-leaf salads stored for 9 days. Feline calicivirus (FCV), a norovirus surrogate, survived on inoculated baby-leaf salads during refrigerated storage (9 days at 7 °C) regardless of treatment. Refrigeration temperatures completely annulled the effectiveness of the EOs against FCV inoculated in baby-leaf salads as occurred in FCV cultures. This study shows that EOs, and zataria in particular, have great potential use as an additional barrier to reduce contamination-related risks in baby-leaf salads. However, further research should be done into foodborne viruses in order to improve food safety.     

Detection of Escherichia coli via VOC profiling using secondary electrospray ionization-mass spectrometry (SESI-MS)

Escherichia coli O157:H7 (EC O157:H7), as well as its recently emerging non-O157 relatives, are a notorious group of pathogenic bacteria associated with foodborne outbreaks. In this study, we demonstrated that secondary electrospray ionization mass spectrometry (SESI-MS) could be a rapid and accurate detection technology for foodborne pathogens. With SESI-MS volatile organic compound (VOC) profiling, we were able to detect and separate a group of eleven E. coli strains from two major foodborne bacteria, Staphylococcus aureus and Salmonella Typhimurium in three food modeling media. In addition, heatmap analysis of relative peak intensity show that there are six core peaks (m/z of 65, 91, 92, 117, 118 and 119) present and at a similar intensity in all eleven E. coli strains at the experimental conditions we tested. These peaks can be considered conserved VOC biomarkers for E. coli species (robustly produced after just 4 h of growth). Bacterial strain-level differentiation was also attempted via VOC profiling, and we found that EC O157:H7 and EC O145 were differentiable from all other EC strains under the conditions investigated.     

Evaluation of Penicillium expansum isolates for aggressiveness, growth and patulin accumulation in usual and less common fruit hosts

Experiments were carried out in vivo and in vitro with four isolates of Penicillium expansum (I 1, E 11, C 28 and I 12) to evaluate their aggressiveness, growth and patulin accumulation in both usual (pears and apples) and less common hosts (apricots, peaches, strawberries and kiwifruits) of the pathogen. The 75% of isolates showed the ability to cause blue mould in all tested hosts. In particular, C 28 and I 1 were the most and the least aggressive isolates, respectively (52.9 and 10.6% infection and 20.7 and 15.4 mm lesion diameters). ‘Candonga’ strawberries and ‘Pinkcot’ apricots showed the largest lesion diameters (29.8 and 25.3 mm), followed by ‘Conference’ pears, ‘Spring Crest’ peaches and ‘Abate Fetel’ pears. With the exception of ‘Candonga’ strawberries, the formation of colonies and mycelial growth of P. expansum isolates on fruit puree agar media (PAMs) was stimulated in comparison to a standard growth medium (malt extract agar, MEA). Two of the most aggressive isolates in our assays (I 12 and C 28) showed the greatest accumulation of patulin both in vitro and in vivo, while the least aggressive isolate (I 1) produced patulin only in a few growth media and cvs. Patulin concentration on fruit PAMs was higher than patulin detected in infected fruit tissues. Apple PAMs were the more favorable substrates for patulin accumulation in vitro (maximum concentration 173.1 and 74.1 μg/mL in ‘Pink Lady and ‘Golden Delicious’ PAMs, respectively) and ‘Pink Lady’ apples inoculated with the isolate E 11 showed the greatest accumulation of patulin in the whole in vivo assay (33.9 μg/mL). However, infected tissue of cv Golden Delicious showed lower average accumulation of patulin (1.7 μg/mL) than that of cv Pink Lady (19.1 μg/mL), and no significant differences in patulin concentrations were found among ‘Golden Delicious’ apples and tested cvs of pears, kiwifruits and strawberries. Peaches were highly susceptible to patulin accumulation, showing average concentrations of 27.4 and 18.6 μg/mL in vitro and in vivo, respectively. Apricots were also consistently positive for patulin accumulation, both in vitro (average values of 20.1 μg/mL) and in vivo (average values of 9.4 μg/mL). Our study showed the potential of some less common hosts of P. expansum (in particular peaches and apricots) to support patulin production, indicating that a steady monitoring of patulin contamination should be carried out in fruit substrates other than apples and pears.     

Application of high hydrostatic pressure to decontaminate green onions from Salmonella and Escherichia coli O157:H7

Consumption of fecally contaminated green onions has been implicated in several major outbreaks of foodborne illness. The objectives of this study were to investigate the survival and growth of Salmonella and Escherichia coli O157:H7 in green onions during storage and to assess the application of high hydrostatic pressure (HHP) to decontaminate green onions from both pathogens. Bacterial strains resistant to nalidixic acid and streptomycin were used to inoculate green onions at low (∼1 log cfu/g) and high (∼2 log cfu/g) inoculum levels which were then kept at 4 or 22 °C for up to 14 days. Both pathogens grew to an average of 5-6 log cfu/g during storage at 22 °C and the bacterial populations were fairly stable during storage at 4 °C. High-pressure processing of inoculated green onions in the un-wetted, wetted (briefly dipped in water) or soaked (immersed in water for 30 min) conditions at 250-500 MPa for 2 min at 20 °C reduced the population of Salmonella and E. coli O157:H7 by 0.6 to >5 log cfu/g, depending on the pressure level and sample wetness state. The extent of pressure inactivation increased in the order of soaked > wetted > un-wetted state. The pressure sensitivity of the pathogens was also higher at elevated treatment temperatures. Overall, after pressure treatment at 400-450 MPa (soaked) or 450-500 MPa (wetted) for a retention time of 2 min at 20-40 °C, wild-type and antibiotic-resistant mutant strains of Salmonella and E. coli O157:H7 inoculated on green onions were undetectable immediately after treatment and throughout the 15-day storage at 4 °C. The pressure treatments also had minimal adverse impact on most sensorial characteristics as well as on the instrumental color of chopped green onions. This study highlights the promising applications of HHP to minimally process green onions in order to alleviate the risks of Salmonella and E. coli O157:H7 infections associated with the consumption of this commodity.     

Evaluation of wash treatments for survival of foodborne pathogens and maintenance of quality characteristics of fresh-cut apple slices

A commercial and three experimental wash treatments for fresh-cut apple slices were evaluated for their ability to affect survival of foodborne pathogens and to maintain quality characteristics measured instrumentally and by sensory analysis. For each apple variety (Fuji and Granny Smith), instrumental firmness, cut surface color, and sensory scores for firmness and flavor of fresh-cut apple slices treated with the commercial and experimental wash solutions were similarly maintained during storage (6 days at 5°C). Prior to their use with apple slices, all three experimental wash solutions reduced the survival of Salmonella serovar Typhimurium and Vibrio cholera by 5 logs or more and the experimental solution at pH 2.0 also reduced survival of Escherichia coli O157:H7, Listeria monocytogenes and Shigella flexneri by at least 5 logs, whereas the commercial wash solution had antibacterial activity only against V. cholera. During treatment of apple slices, the wash solutions changed compositionally over time as indicated by a decrease in conductivity, increases in soluble solids content and osmolality, and changes in pH; and they lost their antibacterial activity. Keeping microbial safety in view, wash solutions should not be reused on multiple batches of sliced apples. Instead, alternative washing strategies that maintain the antimicrobial properties of the wash solutions need to be developed for fresh-cut apple slices.     

The effects of temperature,chlorine and acids on the survival of Listeria and Salmonella strains associated with uncooked shrimp carapace and cooked shrimp flesh

The purpose of this study was to assess the influence of the association of Listeria and Salmonella with shrimp surfaces on the effects of temperature, chlorine and acids on their survival. Planktonic, attached and colonized cells of Listeria monocytogenes Scott A, L. monocytogenes V7, Salmonella Senftenberg 1734b and S. Typhimurium ATCC 14028 were challenged with high (50°, 60° and 70 °C) and low (4 °C) temperature, 100 ppm sodium hypochlorite solution, and acetic, hydrochloric and lactic acids (pH 4.0). Attached and colonized Listeria and Salmonella showed significantly greater (p < 0.05) resistance to heat (∼1.3–2.6 fold increase in D-values), hypochlorite (∼6.6 ≥ 40.0 fold) and acids (∼4.0–9.0 fold) than their planktonic counterparts. There were no significant differences (p > 0.05) in the survival of planktonic, attached or colonized cells of Listeria and Salmonella stored under refrigerated conditions. The association of Listeria and Salmonella with shrimp surfaces enhances their resistance to heat, chlorine and acids. Both attachment to, and subsequent colonization of, shrimp surfaces by pathogens may reduce the efficacy of methods used in their control. Strategies to reduce attachment of these pathogens to shrimp are required to assure safety of this product.     

Individual and combined application of dry heat with high hydrostatic pressure to inactivate Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Alfalfa sprouts are recurrently implicated in outbreaks of food-borne illnesses as a result of contamination with Salmonella or Escherichia coli O157:H7. In the majority of these outbreaks, the seeds themselves have been shown to be the most likely source of contamination. The aims of this study were to comparatively assess the efficacy of dry heat treatments alone or in conjunction with high hydrostatic pressure (HHP) to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Dry heat treatments at mild temperatures of 55 and 60 °C achieved ≤1.6 and 2.2 log CFU/g reduction in the population of Salmonella spp. after a 10-d treatment, respectively. However, subjecting alfalfa seeds to more aggressive temperatures of 65 °C for 10 days or 70 °C for 24 h eliminated a ∼5 log population of Salmonella and E. coli O157:H7. We subsequently showed that the sequential application of dry heating followed by HHP could substantially reduce the dry heating exposure time while achieving equivalent decontamination results. Dry heating at 55, 60, 65 and 70 °C for 96, 24, 12 and 6 h, respectively followed by a pressure treatment of 600 MPa for 2 min at 35 °C were able to eliminate a ∼5 log CFU/g initial population of both pathogens. Finally, we evaluated the impact of selected treatments on the seed germination percentages and yield ratios and showed that dry heating at 65 °C for 10 days did not bring about any considerable decrease in the germination percentage. However, the sprout yield of treated alfalfa seeds was reduced by 21%. Dry heating at 60 and 65 °C for 24 and 12 h respectively followed by the pressure treatment of 600 MPa for 2 min at 35 °C did not significantly (P > 0.05) affect the germination percentage of alfalfa seeds although a reduction in the sprouting yield was observed.     

Multiplex fiber optic biosensor for detection of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica from ready-to-eat meat samples

Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica are the most common foodborne bacterial pathogens and are responsible for many outbreaks. Therefore, multiplex detection of these three using a single assay platform is highly desirable. The objective was to develop and optimize a fiber optic sensor for simultaneous detection of these three from food. The streptavidin coated optical waveguides were immobilized with biotinylated polyclonal antibodies and exposed to the bacterial suspensions or enriched food samples for 2 h. Pathogens were detected after reacting with Alexa-Fluor 647-labeled monoclonal antibodies. Ready-to-eat beef, chicken and turkey meats were inoculated with each pathogen (∼100 cfu/25 g), enriched in SEL (Salmonella, E. coli, Listeria), a multipathogen selective enrichment broth for 18 h and tested with the biosensor. The biosensor was able to detect each pathogen, individually or in a mixture with very little cross-reactivity. The limit of detection for the sensor was ∼10³ cfu/ml for all three pathogens. Furthermore, the biosensor successfully detected each pathogen, grown in a mixture from enriched meat samples under 24 h. The pathogen presence was further verified by PCR and immunofluorescence assay. The multiplex fiber optic sensor shows promise for detection of the three pathogens if present in the same sample eliminating the use of multiple single pathogen detection platforms.     

Microbiological and physicochemical quality of fresh-cut apple enriched with the probiotic strain Lactobacillus rhamnosus GG

The effectiveness as protective culture of the probiotic Lactobacillus rhamonosus GG (L. rham. GG) against Salmonella and Listeria monocytogenes on minimally-processed apples throughout storage as well as its effect on apple quality and natural microflora was evaluated. Survival to subsequent exposure to gastric stress was also reported. Apples were cut into wedges and dipped in a solution containing Salmonella and L. monocytogenes (10⁵ cfu mL⁻¹) and/or L. rham. GG (10⁸ cfu mL⁻¹). Apple wedges were packed and stored at 5 and 10 °C. Periodically, microbial population, bacterial survival to gastric stress and quality of apple wedges were evaluated. Although Salmonella was not affected by co-inoculation with L. rham. GG, L. monocytogenes population was 1-log units lower in the presence of L. rham. GG. L. rham. GG population maintained over recommended levels for probiotic action (10⁶ cfu g⁻¹) along storage, however, viable cells after gastric stress were only above this level during the first 14 days. Pathogen survival after gastric stress was <1% after 7 days at 5 °C. Moreover, apple wedges quality was not affected by L. rham. GG addition. Thus, L. rham. GG could be a suitable probiotic for minimally-processed apples capable to reduce L. monocytogenes growth; nevertheless shelf life should not be higher to 14 days to guarantee the probiotic effect.     

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus in vitro were investigated. Cranberry concentrate at various concentrations was prepared in distilled water (DW) or Brain Heart Infusion (BHI) broth. Pathogens were inoculated in each sample and incubated at 21 and 4 °C for 0, 1, 5, 7, and 24 h (DW samples) and 0, 1, 3, and 5 days (BHI samples). Transmission electron microscopy (TEM) was used to study the effects of cranberry concentrate on cellular structure of pathogens. DW results showed that S. Typhimurium and L. monocytogenes were reduced to non-detectable levels at 5 h in 100 μl/ml treatment at 21 and 4 °C. At 24 h, no target pathogens were detected from the 100 μl/ml treatment. BHI data indicated that the 100 μl/ml treatment reduced the four pathogens by 3-8 log CFU/ml compared with the control on Day 5 at 21 and 4 °C. TEM revealed damage to the bacterial cell walls and membranes. Cranberry concentrate has antibacterial effects on the four foodborne pathogens. Based on potential health benefits and proven antimicrobial effects, American cranberry concentrate may have dual applications as a food preservative.     

Dual effectiveness of sodium chlorite for enzymatic browning inhibition and microbial inactivation on fresh-cut apples

The dual effectiveness of sodium chlorite for browning inhibition and microbial inactivation on fresh-cut apples was investigated and compared to other anti-browning and antimicrobial agents. Results indicate that sodium chlorite significantly (P < 0.001) inhibited the browning reaction of fresh-cut Red Delicious apples stored at 5 °C for 14 days. This treatment also significantly reduced polyphenol oxidase activities. Treatments with acidified sodium chlorite, calcium chloride, or calcium ascorbate exhibited strong inhibition on apple browning during the early storage, these treatment effects diminished after 7 days in storage. Combining calcium chloride with sodium chlorite further significantly (P < 0.001) improved the firmness of apple slices, and browning inhibition during storage. Additionally, treatments with acidified sodium chlorite, sodium chlorite, or the combination of sodium chlorite and calcium chloride significantly (P < 0.001) reduced Escherichia coli populations on fresh-cut apples by 3.0, 3.6, and 3.9 log cfu g⁻¹ over the water control. The dual effectiveness of sodium chlorite to inhibit enzymatic browning and inactivate E. coli may allow this compound to achieve a prominent role in improving the quality and safety of products in the fresh-cut apple and other food industries.     

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice with gaseous ozone

This research was initiated to assess the efficacy of gaseous ozone for inactivation Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice. Juice samples with solids content of 18, 36, and 72 °Brix inoculated with a culture cocktail of three foodborne pathogens were treated with gaseous ozone at a flow rate of 3.0 L/min and an ozone generation rate of 0.10, 0.90, 3.51, and 5.57 g/h for 0.5, 1, 5, and 10 min, respectively. The inactivation kinetics of gaseous ozone on foodborne pathogens conformed to the Weibull model. The time required to achieve a 5 log reduction (t_5d) was estimated using the parameters of the Weibull model. The t_5d increased with increasing solids content of apple juice. The ozone generation rate did not impart a significant effect (p > 0.05) on t_5d. Gaseous ozone is effective at inactivating foodborne pathogens in apple juice but the efficacy is dependent on the solids content of the juice sample.