Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N₂ or without flushing with N₂, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly ( P > 0.05). Flushing packages of lettuce with 100% N₂ followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua , strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes , it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N₂ flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.     

Effects of storage atmosphere on Listeria monocytogenes and competing microflora using a surface model system

A solid-surface model system was used to study the effects of gas atmospheres encountered in modified atmosphere packaging of vegetables on the survival and growth of Listeria monocytogenes and competing micro-organisms. The effects of increasing CO₂ levels (from 5% to 20%), 100% N₂ and 3% O₂ were determined. The model system allowed for estimation of the growth of L. monocytogenes alone or in the presence of competing microflora. CO₂ concentrations of 5–10% (with 5% O₂ in N₂) had no inhibitory effect, by comparison with air, on the growth and survival of pure cultures of L. monocytogenes . At 20% CO₂ population densities were reduced up to day 8, but the final population densities reached were not. An atmosphere of 100% N₂ allowed survival of pure cultures of L. monocytogenes , but populations did not significantly change ( P  > 0.05) during storage, whereas a low O₂ (3%, balance N2) atmosphere allowed significant growth ( P  < 0.05) of L. monocytogenes . Growth and inhibitory activities of Enterobacter cloacae and E. agglomerans were inversely related to the concentration of CO₂. By contrast, the growth and anti-listerial activities of Leuconostoc citreum increased with elevated CO₂ concentrations. In the low O₂ atmosphere, L. monocytogenes grew considerably better in the presence of populations from the indigenous microflora of lettuce than when in pure culture. The results indicate that the gas atmospheres present within modified atmosphere packages of minimally processed vegetables may affect the interactions between the pathogen and the natural competitive microflora sufficiently to indirectly enhance L. monocytogenes growth.     

Thermal Inactivation of Salmonella Senftenberg and Listeria innocua in Beef/Turkey Blended Patties Cooked via Fryer and/or Air Convection Oven

ABSTRACT: Beef/turkey blended patties, containing 10⁷ to 10⁸ cfu/g of Salmonella Senftenberg or Listeria innocua , were battered and breaded. The effect of frying (177 °C) and air convection cooking (288 °C) on thermal inactivation of S. Senftenberg and L. innocua was evaluated. A model was obtained to correlate product internal temperature with frying and oven cooking time. Cooking method significantly affected thermal history and subsequently the thermal inactivation of S. Senftenberg and L. innocua. The effect of frying time interacted with oven cooking time. Increasing frying time reduced the oven cooking time. Mathematical models were developed to correlate the survival rate of S. Senftenberg or L. innocua with frying and oven cooking time.     

Effects of acid adaptation on the survival of Listeria monocytogenes on modified atmosphere packaged vegetables

The survival and growth of Listeria monocytogenes and L. innocua on ready-to-use (RTU) packaged vegetables (lettuce, swedes, dry coleslaw mix, bean-sprouts) were studied. The effects of acid adaptation of Listeria spp. on their survival during subsequent storage were also investigated. Listeria innocua behaviour was similar to that of L. monocytogenes on all vegetables examined. The survival and growth patterns of Listeria varied with the packaged product. Populations on packaged lettuce and swedes significantly increased ( P  < 0.05, by 1–1.5 log cycles) during a 14-day storage period. During the same period, Listeria counts gradually decreased (by 1–1.5 log cycles) on coleslaw mix. Acid adaptation enhanced survival of Listeria spp. during storage in packages of vegetables which had relatively high in-pack CO₂ levels (i.e. 25% in packaged coleslaw, bean-sprouts). It is concluded that adapting listerial cells to mildly acidic conditions rendered cultures more resistant to relatively high (25–30%) CO₂ atmospheres.     

Evaluation of Listeria innocua as a suitable indicator for replacing Listeria monocytogenes during ripening of Camembert cheese

The suitability of Listeria innocua for use as an indicator for replacing Listeria monocytogenes during the cheese-making and ripening of Camembert cheese was evaluated. Pasteurized whole milk inoculated with either L. innocua or L. monocytogenes was used to make Camembert cheese, which were ripened in three stages. All cheese was ripened in three stages: room temperature (∼20 °C) and relative humidity of 60% for 36 h; 12 °C and relative humidity of 93% for 2 weeks; and 7 °C and relative humidity of 85% for 3 weeks. Results showed that population values of L. innocua and L. monocytogenes on day 1 were 7.16 and 6.11 log₁₀ CFU/g, respectively, which declined to 6.54 and 5.45 log₁₀ CFU/g, respectively, during subsequent 20 days. Thereafter, L. innocua and L. monocytogenes populations increased to 7.38 and 6.06 log₁₀ CFU/g on day 35 of ripening, respectively. During ripening, surface and interior of cheeses were analysed for populations of L. innocua and L. monocytogenes , respectively. The data were collected on day 1, 5, 10, 15, 20, 25, 30, and 35 of ripening. Generally, the growth of L. innocua and L. monocytogenes is faster in surface than in centre. Top centre, bottom centre and bottom surface locations had similar population values during ripening. There were no significant differences ( P  > 0.05) between batch and section of cheese. The ripening time and locations had significant effect ( P  < 0.05) on the survival and growth of L. innocua and L. monocytogenes . The trends of survival and growth of L. innocua and L. monocytogenes were similar. These results indicated that L. innocua can be considered as an indicator for L. monocytogenes during ripening of Camembert cheese.     

INFLUENCE OF WASHING TREATMENT ON NATIVE MICROFLORA AND ESCHERICHIA COLI POPULATION OF INOCULATED CANTALOUPES

The influence of chlorine or hydrogen peroxide treatment on populations of Escherichia coli 25922 on the external surface of inoculated cantaloupe was investigated. Surface treatment with 70% EtOH, followed by immersion in 10⁸ CFU/mL E. coli inoculum deposited an average of 4.4 log₁₀CFU/cm² cell population on the cantaloupe surface. The efficncy of washing inoculated cantaloupe was dependent on storage interval between inoculation and treatment. Dipping the cantaloupes in solutions containing 1000 mg/L chlorine or 5% peroxide for 5 min, within 24 h of inoculation, caused a 2 log₁₀ CFU/cm² reduction of the indigenous surface microflora and a 3–4.0 log₁₀ CFU/cm² reduction in E. coli. The efficacy was less when the interval between inoculation and treatment exceeded 24 h. Chlorine appeared in be a better antimicrobial agent than hydrogen peroxide against F. coli ATCC 25922 inoculated on cantaloupe surfaces while hydrogen peroxide was better in reducing surface microflora of cantaloupe.     

Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products

ABSTRACT:  The impact of sodium nitrite (NaNO₂) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO₂) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 × 10³ L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 °C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 °C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 × 10⁴ to 1 × 10⁵ CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO₂ (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX^® System (DuPont™ Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria -positive food samples and were consistently superior to and significantly different ( P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.     

Effect of Steam- and Hot-Water Post-Process Pasteurization on Microbial and Physical Property Measures of Fully Cooked Vacuum-Packaged Chicken Breast Strips

ABSTRACT: The microbial inactivation was conducted using fully cooked chicken breast strips that were surface-inoculated with Listeria innocua (10⁷ colony forming unit per gram product), vacuum packaged, and treated by steam or hot water at 88 °C for 10 to 35 min. The studies for physical properties were conducted using uninoculated products that were treated for 25 to 35 min. Both steam and hot water treatments were effective in inactivating L. innocua in the packaged products. No significant difference was found on the survivors of L. innocua between steam and hot water treatments. No significant difference was found on water activity and shear force among the treated and untreated products. However, significant difference was found on expressible and total moisture among treated and untreated products. This study showed that post process pasteurization with hot water or steam lowered microbial populations but affected the water purge from the products.     

Evaluation of liquid smoke treated ready-to-eat (RTE) meat products for control of Listeria innocua M1

ABSTRACT:  Liquid smoke fractions (S1, S2, S3, and S4) were applied on ready-to-eat (RTE) meat products to control the growth of inoculated Listeria innocua M1. Turkey rolls and roast beef products were dipped in liquid smoke, surface inoculated with L. innocua M1 (10² CFU/25 cm² RTE meat surface), vacuum packaged, and stored at 4 °C. Section 8.5 of USDA's detection and isolation procedure for L. monocytogenes was employed in conjunction with a Micro-ID™ system for L. innocua M1 identification (ID). Products treated with smoke fractions S1, S2, and S3 were negative for L. innocua M1 at 2 and 4 wk during incubation at 4 °C. Products treated with S4 were positive for L. innocua M1 immediately following inoculation and after storage for 2 and 4 wk. Smoke fractions S1, S2, and S3 exhibited pH values lower than 4.6, acidity values higher than 1.5%, and carbonyl concentrations higher than 110 mg/mL. All liquid smoke fractions contained similar phenol concentrations (0.3 to 0.6 mg/mL), suggesting that phenols may have a limited role in the bactericidal effects of liquid smoke fractions against specific microorganisms.     

Inactivation of Listeria monocytogenes on Beef Bologna and Cheddar Cheese Using Polyvinyl-idene Chloride Films Containing Sorbic Acid

ABSTRACT: Polyvinylidene chloride (PVDC, Saran^R F-310) films containing sorbic acid (0%, 1.5%, and 3.0% w/v) were prepared with use of a solvent-casting method and were then placed between slices of commercially produced beef bologna that were previously surface-inoculated with L. monocytogenes at 10³ or 10⁵ CFU/g. In addition, cubes of commercial Cheddar cheese were surface-inoculated to contain 10³ or 10⁵ Listeria monocytogenes colony-forming units (CFU) /g and then wrapped with the sorbic acid-containing films. Films containing 1.5% and 3.0% (w/ v) sorbic acid prevented growth of L. monocytogenes on bologna slices with populations as much as 7.1 logs lower after 28 d of storage at 4 °C compared with the sorbic acid-free controls. In contrast, numbers of Listeria remained relatively stable on Cheddar cheese with populations decreasing < 1.3 logs after 35 d of storage. With use of the sorbic acid-containing films, common spoilage organisms were also inhibited on both products. After 28 d of contact with bologna and Cheddar cheese, these films retained 7% and 60% of their original sorbic acid content, respectively, with the control film retaining 85% of its original sorbic acid content. Given these findings, sorbic acid-containing films may be useful in enhancing the safety and shelf-life of ready-to-eat delicatessen products.     

THE EFFECT OF AEROBIC MESOPHILIC MICROFLORAL LEVELS ON THE ISOLATION OF INOCULATED LISTERIA MONOCYTOGENES STRAIN LM82 FROM SELECTED FOODS

The effect of aerobic mesophilic microfloral concentration on the isolation of Listeria monocytogenes LM82 was studied in 31 (18 cheeses and 7 noncheese) retail foods having standard plate counts of 10¹ to 10⁸ colony forming units (CFU)/g. Foods were spiked with L. monocytogenes and enriched at 30°C for 24 h in a selective enrichment broth used in a U.S. Food and Drug Administration method. Inoculum levels for isolation on modified McBride agar ranged from 0.1 to > 5 × 10³ with a geometric mean value of 5 inoculated CFU/g or 1.4 CFU/g. Pure Enterococcus (Streptococcus) faecalis ( 0 to 6 × 10⁶ inoculated CFU/mL ) in the absence of food matrix had no effect on the enrichment of L. monocytogenes. Ease of isolation of LM82 was independent of the food microflora concentration both generally and in the specific food type of 9 Brie cheeses. Competition, when it occurs, therefore, may be due to specific bacterial competitors rather than bacterial numbers .     

SURVIVAL OF SALMONELLA TYPHIMURIUM, LISTERIA MONOCYTOGENES AND INDICATOR BACTERIA ON COOKED UNCURED TURKEY LOAF STORED UNDER VACUUM AT 3°C

Sterile slices of cooked uncured turkey loaf were inoculated with 10⁶ CFU of either Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Enterococcus faecalis, Citrobacter freundii, Klebsiella pneumoniae, or Enterobacter cloacae. Inoculated samples were vacuum-packaged and stored at 3 ± 1°C. Microorganisms were enumerated at 0, 3, 6, 9, 12, and 15 days on nonselective media . K. pneumoniae exhibited the least cold-tolerance with a log₁₀ 1.70 decrease in numbers. The coliforms E. cloacae, E. coli, and C. freundii had a survival pattern similar to that of S. typhimurium, with population decreases of log₁₀ 0.65, 0.82, 1.13, and 0.79, respectively . E. faecalis and L. monocytogenes were significantly more cold-resistant, with a decrease of log₁₀ 0.20 and no significant change in numbers, respectively. Survival of E. faecalis was not significantly (p < 0.01) different than that of L. monocytogenes, suggesting the use of enterococci as indicators of L. monocytogenes contamination of processed meats .     

Quality of Shredded Carrots as Affected by Packaging Film and Storage Temperature

ABSTRACT: Different packaging films and storage temperatures were used to establish a range of equilibrium modified atmospheres for storage of shredded carrots. Quality and storage-life of the packaged shredded carrots were determined using sensory evaluation, microbial counts, and a range of physical tests. Minimal processing steps such as peeling and shredding caused physical damage, physiological stress, and enhanced microbial growth, leading to a reduced shelf life when compared to the whole vegetable. A P-plus microporous film (CO₂ permeability of 29 X 10³mL.m ^-2.d ^-1.atm ^-1) was the most suitable for the storage of shredded carrots. Findings indicated that deterioration in these products was triggered by the depletion of oxygen more than by the rise in carbon dioxide.     

Elimination of Listeria monocytogenes in soft and red smear cheeses by irradiation with low energy electrons

Soft and red smear cheeses are frequently contaminated by Listeria monocytogenes , sometimes at relatively high concentration (< 10⁵ CFUg^-1). This bacterium is radiosensitive (D₁₀ value of approximately 0.45 kGy) but irradiation of the whole cheese by X-rays induced off-flavours when the dose exceeded 1.0 kGy. Irradiation could be effective in eliminating L. monocytogenes only from lightly contaminated cheeses (> 10²CFU g^-1).
L. monocytogenes appears only in the rind (where the pH is greater than 6.3) and never grows in the core of the cheese. Under these conditions, a specific irradiation of the rind after ripening, with a low-energy electron beam at relatively high doses (up to 3.0 kGy), allows the total elimination of L. monocytogenes in heavily contaminated samples (10⁵-10⁶ CFU g^-1) without noticeable modifications of the organoleptic properties of the cheese.     

Identification of Listeria innocua surrogates for Listeria monocytogenes in hamburger patties

ABSTRACT:  Listeria innocua M1 has been used by many researchers as a nonpathogenic thermal processing surrogate for Listeria monocytogenes . However, L. innocua M1 has been criticized because its thermal survivability characteristics are not as closely parallel to L. monocytogenes as some would like in a variety of foods and processing conditions. The present study was conducted to compare multiple L. innocua and L. monocytogenes strains to validate L. innocua M1 as the ideal surrogate under high-temperature thermal processing conditions for L. monocytogenes . The D - and z -values of L. innocua M1, L. innocua strain SLCC 5639 serotype (6a), SLCC 5640 (6b), SLCC 2745 (4ab), and L. monocytogenes F4243 (4b) were calculated for raw hamburger patties. Hamburger patties were inoculated with 10^7–8 CFU/g of L. monocytogenes or L. innocua . Samples were heat treated at 4 temperatures (62.5 to 70 °C). At each temperature, the decimal reduction time ( D -value) was obtained by linear regression of survival curves. The D - and z -values were determined for each bacterium. The D -values of L. innocua and L. monocytogenes serotypes ranged from 3.17 to 0.13 min at 62.5 to 70 °C, and the z -values of L. innocua and L. monocytogenes were 7.44 to 7.73 °C. Two of the 4 L. innocua serotypes used in this experiment have the potential for use as surrogates in hamburger meat with varying margins of safety. L. innocua M1 should serve as the primary nonpathogenic surrogate with the greatest margin of safety in verifying a new thermal process to destroy L. monocytogenes .     

Incorporation of the Antilisterial Bacteriocin-like Inhibitory Substance from Pediococcus parvulus VKMX133 into Film-forming Protein Matrices with Different Hydrophobicity

ABSTRACT: The antilisterial bacteriocin-like inhibitory substance (BLIS) produced by Pediococcus parvulus VKMX133 was incorporated into protein film matrices of ethanol-soluble corn zein (CZ), and water-soluble whey protein isolate (WPI). Various BLIS concentrations were added to film-forming solutions (FFS), cast, dried, and cut in circular sections (28.27 mm²). Antimicrobial activity of films was evaluated by measuring inhibition zones against Listeria innocua ATCC 33090 on tryptic soy broth (TSB) agar. BLIS released from films into water at 10 °C was determined. Film effectiveness was evaluated by measuring the reduction of L. innocua population (10⁸ colony-forming units [CFU]/mL) in peptone water where film sections were immersed. Film topography was analyzed by scanning electron microscopy (SEM). The minimum BLIS concentration in FFS to generate films with antimicrobial activity was 833 and 3333 arbitrary units per milliliter (AU/mL) for CZ and WPI, respectively. BLIS released into water was detected only for CZ films. Antimicrobial CZ films were more effective in reducing L. innocua population than WPI films at the same BLIS concentrations. SEM showed that surface topography was porous for CZ and more closed and compact for WPI films. BLIS can be entrapped into film protein matrices to produce edible antimicrobial packaging. However, BLIS inhibitory action against L. innocua and release were dependent on film nature and topography, and probably on hydrophobic and electrostatic interactions arising between the protein matrices and BLIS. High concentration of bacteriocin in films does not necessarily improve their effectiveness against L. innocua.     

USE OF MEAT ISOLATE, LACTOBACILLUS BAVARICUS MN, TO INHIBIT LISTERIA MONOCYTOGENES GROWTH IN A MODEL MEAT GRAVY SYSTEM

The ability of Lactococcus lactis 11454 , Pediococcus pentosaceus 43200 and Lactobacillus bavaricus MN, originally isolated from dairy, vegetable, and meat products, respectively, to inhibit growth of Listeria monocytogenes Scott A in a model beef gravy was examined. In the first series of experiments, where the lactic acid bacteria and L. monocytogenes were inoculated at levels of 10⁵ CFU/mL and 10³ CFU/mL, respectively only L. bavaricus inhibited listerial growth at 10C. Subsequent experiments using L. bavaricus MN confirmed that the inhibition was caused by a bacteriocin, occurred at temperatures at low as 4C, and could be initiated by 10³ CFU/mL L. bavaricus in the presence of L. monocytogenes at levels 10-fold higher. Although the inhibitory agent was protease-sensitive and inhibition occurred in the absence of a fermentable carbohydrate, the presence of acid enhanced efficacy of the bacteriocin .     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

Modelling the competitive growth of Listeria monocytogenes and Listeria innocua in enrichment broths

The overgrowth of Listeria innocua in enrichment broths designed for the isolation of Listeria monocytogenes is believed to result from two factors: a selective growth advantage of L. innocua, and/or an inhibitory interspecies interaction. The generation times of 13 isolates of L. innocua and L. monocytogenes were determined in Brain Heart Infusion (BHI) and a variety of enrichment media. No significant differences were found in growth characteristics between either species in the various media, suggesting that the growth advantage of L. innocua in enrichment media was not as significant as previously described. Kinetic analysis of mixed cultures of L. monocytogenes and isolates of L. innocua producing a variety of inhibitory activities demonstrated the possibility of an inhibitory interaction between these two species resulting in the overgrowth of the enrichment culture with L. innocua. Modelling the evolution of the ratio between two populations in an enrichment process was used to analyze the impact of a selective growth advantage in L. innocua in an enrichment process for growth of L. monocytogenes. These findings support the widely held view that an overgrowth of L. innocua in the enrichment process can result from both a selective growth advantage as well as the production of inhibitory compounds. From a practical perspective, these interactions can result in an increase in false negatives.     

Inhibition of foodborne pathogens by native microflora recovered from fresh peeled baby carrot and propagated in cultures

ABSTRACT:  The inhibitory effect of fresh peeled baby carrot and associated microflora on the viability and growth of Listeria monocytogenes , Yersinia enterocolitica , Salmonella enterica , Escherichia coli O157:H7, and Pseudomonas marginalis was investigated. The population of viable L. monocytogenes was reduced by more than 2 logs following the dipping of sliced baby carrots in the bacterial suspension for 2 min. However, other pathogens subjected to the same treatment showed no reduction in the population. Surface sanitization of baby carrots reduced the number of native microflora and in turn increased the growth of each pathogen on this commodity by 2 to 3 logs. Filter-sterilized carrot homogenates exhibited no antimicrobial activity and were capable of supporting the growth of each pathogen to a density of over 2 × 10⁹ CFU/mL. However, the growth of each pathogen in carrot homogenates containing microflora recovered from baby carrot and propagated in tryptic soy broth was reduced 2 to 3 logs after incubation at 28 °C for 2 d. On pepper disks, which have no antilisterial activity and very low levels of background microflora, the addition of carrot microflora also reduced the growth of each pathogen 2 to 4 logs after 2 d at 20 °C. The reduction was dependent upon the ratio between the number of carrot microflora and pathogen tested. The growth of L. monocytogenes or Y. enterocolitica on pepper disks containing carrot microflora was almost completely stopped after storage at 8 °C for 8 d. The inhibitory effect of baby carrots on pathogens is in part due to the antimicrobial activity of carrot tissue and in part due to the antagonistic action of associated microflora.