Viability of Salmonella and Listeria monocytogenes in delicatessen salads and hummus as affected by sodium content and storage temperature

A study was conducted to determine survival and growth behavior of Salmonella and Listeria monocytogenes in commercially prepared mayonnaise-based potato salad, macaroni salad, and coleslaw and in hummus (initial mean pH values were 4.80 to 4.94, 4.18 to 4.31, 3.87, and 4.50 to 4.52, respectively) as affected by sodium concentration (133 to 364, 190 to 336, 146 to 272, and 264 to 728 mg/100 g, respectively) and storage at 4 or 10°C for up to 27 days. Salmonella did not grow in any of the test products. Initial populations (2.02 to 2.38 log CFU/g) decreased in coleslaw to undetectable levels (<1 CFU/25 g) within 13 days and in most formulations of macaroni salad within 20 to 27 days. Salmonella survived in highest numbers in potato salad and hummus. The presence of added sodium in macaroni salad stored at 4°C and hummus stored at 4 or 10°C appeared to protect Salmonella against inactivation. L. monocytogenes, at an initial population of 1.86 to 2.23 log CFU/g, did not grow in test products, but with the exception of coleslaw containing sodium at a concentration used in the standard (control) recipe, this pathogen was detected by direct plating (≥ 1.0 log CFU/g) in all products stored at 4 or 10°C for 27 days. L. monocytogenes populations were significantly (P < 0.05) lower in potato salad and hummus with no added sodium than in test products with added sodium after storage at 4°C. Sodium concentration did not markedly affect aerobic plate counts over the 27-day storage period. Results confirm that the acidic pH of mayonnaise-based salads and hummus is a major factor preventing growth and influencing rates of inactivation of Salmonella and L. monocytogenes. In the absence of added sodium, death of these bacteria may be more rapid. However, in general decreasing or increasing the sodium concentration in selected delicatessen salad and hummus recipes does not markedly affect the behavior of Salmonella and L. monocytogenes when products are stored at 4 or 10°C for up to 27 days.     

Growth or Survival of Listeria monocytogenes in Ready-to-Eat Meat Products and Combination Deli Salads During Refrigerated Storage

Growth or survival of Listeria monocytogenes in cold‐smoked salmon; sliced, cooked ham; sliced, roasted turkey; shrimp salad; and coleslaw obtained at retail supermarkets stored at 5 °C, 7 °C, or 10 °C (41 °F, 45 °F, or 50 °F, respectively) for up to 14 d was evaluated. Cold‐smoked salmon, ham, and turkey were obtained in case‐ready, vacuum packages. All food products were stored aerobically to reflect additional handling within the retail supermarket. Cold‐smoked salmon, ham, and turkey supported the growth of L. monocytogenes at all 3 storage temperatures. Fitted growth curves of initial populations (about 3 log₁₀ colony‐forming units [CFU]/g) in cold‐smoked salmon, ham, and turkey stored at 5 °C achieved maximal growth rates of 0.29, 0.45, and 0.42 log₁₀ CFU/g growth per day, respectively. Storage at 10 °C increased the estimated maximal growth rate of the pathogen by 0.56 to 1.08 log₁₀ CFU/ g growth per day compared with storage at 5 °C. A decline in populations of L. monocytogenes was observed in shrimp salad and coleslaw, and the rate of decline was influenced by storage temperature. Retention of viability was higher in shrimp salad than in coleslaw, where populations fell 1.2, 1.8, and 2.5 log₁₀ CFU/g at 5 °C, 7 °C, and 10 °C, respectively, after 14 d of storage. Inability of shrimp salad and coleslaw to support the growth of L. monocytogenes may be attributed to the acidic pH (4.8 and 4.5, respectively) of the formulations used in this study. Results show that the behavior of L. monocytogenes in potentially hazardous ready‐to‐eat foods is dependent upon the composition of individual food products as well as storage temperature.     

Growth potential of Salmonella enterica in thirty-four different RTE vegetable salads during shelf-life

Thirty-four different ready-to eat (RTE) vegetable salads were inoculated with a cocktail of three Salmonella enterica strains, and stored under a modified atmosphere for up to 168 h at 4, 7, 12 and 16°C. Eighteen (18) of the salad samples comprised of two or more vegetable ingredients (also referred to as MV RTE salads), and 16 were made up of single vegetable ingredients (SV RTE salads). Generally, the growth potential of inoculated S. enterica varied depending on temperature and type of RTE vegetable salad. The higher temperature was generally more favourable for the growth of S. enterica. Among all 34 salad samples, 5, 11, 18 and 24 salad samples supported the growth of Salmonella at 4, 7, 12 and 16°C, respectively. All salads consisting of multiple vegetable ingredients except two: one comprised of carrots, lettuce and beetroot and another comprised of white cabbage and purple cabbage, supported the growth of Salmonella at high temperatures (either 12 or 16 or both 12 and 16°C). Although the growth of Salmonella was variable in the different types of RTE salads, and growth was generally low at 4°C, Salmonella exhibited consistently minimal growth in some vegetable salads such as those comprised of carrots, lettuce and beetroot, carrots, beetroots, cabbage and cucumber, as well as one comprised of beetroot and corn at all temperature conditions tested.     

Statistical distributions describing microbial quality of surfaces and foods in food service operations

Data on the microbial quality of food service kitchen surfaces and ready-to-eat foods were collected over a period of 10 years in Rutgers University dining halls. Surface bacterial counts, total aerobic plate counts, and total and fecal coliform counts were determined using standard methods. Analysis was performed on foods tested more than 50 times (primarily lunch meats and deli salads) and on surfaces tested more than 500 times (36 different surfaces types, including pastry brushes, cutting boards, and countertops). Histograms and statistical distributions were determined using Microsoft Excel and Palisades Bestfit, respectively. All data could be described by lognormal distributions, once data above and below the lower and upper limits of detection were considered separately. Histograms for surfaces counts contained one peak near 1 CFU/4 cm2. Surfaces with higher levels of contamination tended to be nonmetal, with the exception of buffalo chopper bowls, which commonly had high counts. Mean counts for foods ranged from 2 to 4 log CFU/g, with shrimp salad, roast beef, and bologna having higher means. Coleslaw, macaroni salad, and potato salad (all commercially processed products, not prepared in the dining halls) had lowest overall means. Coliforms were most commonly found in sealeg salad (present in 61% of samples) and least commonly found in coleslaw (present in only 7% of samples). Coliform counts (when present) were highest on average in shrimp salad and lowest in coleslaw. Average coliform counts for most products were typically between 1 and 2 log most probable number per gram. Fecal coliforms were not typically found in any deli salads or lunch meats.     

Dynamic predictive model for the growth of Salmonella spp. in liquid whole egg

Abstract: A dynamic model for the growth of Salmonella spp. in liquid whole egg (LWE) (approximately pH 7.8) under continuously varying temperature was developed. The model was validated using 2 (5 to 15 °C; 600 h and 10 to 40 °C; 52 h) sinusoidal, continuously varying temperature profiles. LWE adjusted to pH 7.8 was inoculated with approximately 2.5–3.0 log CFU/mL of Salmonella spp., and the growth data at several isothermal conditions (5, 7, 10, 15, 20, 25, 30, 35, 37, 39, 41, 43, 45, and 47 °C) was collected. A primary model (Baranyi model) was fitted for each temperature growth data and corresponding maximum growth rates were estimated. Pseudo‐R² values were greater than 0.97 for primary models. Modified Ratkowsky model was used to fit the secondary model. The pseudo‐R² and root mean square error were 0.99 and 0.06 log CFU/mL, respectively, for the secondary model. A dynamic model for the prediction of Salmonella spp. growth under varying temperature conditions was developed using 4th‐order Runge–Kutta method. The developed dynamic model was validated for 2 sinusoidal temperature profiles, 5 to 15 °C (for 600 h) and 10 to 40 °C (for 52 h) with corresponding root mean squared error values of 0.28 and 0.23 log CFU/mL, respectively, between predicted and observed Salmonella spp. populations. The developed dynamic model can be used to predict the growth of Salmonella spp. in LWE under varying temperature conditions. Practical Application: Liquid egg and egg products are widely used in food processing and in restaurant operations. These products can be contaminated with Salmonella spp. during breaking and other unit operations during processing. The raw, liquid egg products are stored under refrigeration prior to pasteurization. However, process deviations can occur such as refrigeration failure, leading to temperature fluctuations above the required temperatures as specified in the critical limits within hazard analysis and critical control point plans for the operations. The processors are required to evaluate the potential growth of Salmonella spp. in such products before the product can be used, or further processed. Dynamic predictive models are excellent tools for regulators as well as the processing plant personnel to evaluate the microbiological safety of the product under such conditions.     

Enterotoxin C2 Production by S. aureus in Entree Salads

Staphylococcus aureus strain 361 was inoculated into salads containing chicken, macaroni, potato, or artificially flavored soy product. Egg was added to some. The pH averaged 6.2 in the control made with water dressing rather than vinegar, 4.7 with home-style cooked salad dressing, and 4.9 with commercial salad dressing. Following incubation at 37°C for 8 or 24 hr, pH, total counts, and enterotoxin C₂ were determined. Enterotoxin was detected at 8 hr in all macaroni and potato dressing types. At 8 hr, enterotoxin was not detected in most soy product or chicken salads. By 24 hr the lowest levels were in the soy product salads but all products contained toxin. When the inoculum level was reduced below the 10⁵ CFU per g used in the main study, enterotoxin production was delayed but occurred at 8 hr if the inoculum level was 10³.     

Inactivation of Salmonella spp. on tomatoes by plant molecules

The efficacy of carvacrol (CAR), trans-cinnamaldehyde (TC), eugenol (EUG) and β-resorcylic acid (BR) as a wash treatment for reducing Salmonella spp. on tomatoes was investigated. Plum tomatoes inoculated with a six-serotype mixture of Salmonella (10⁸ CFU) were subjected to washing in sterile deionized water (control) or deionized water containing chlorine (100 ppm), CAR (0.25 and 0.75%), TC (0.5 and 0.75%), EUG (0.25 and 0.75%), or BR (0.75 and 1.0%) for 15 sec, 1 min, and 3 min. The plant molecules were more effective (P < 0.05) in reducing Salmonella on tomatoes compared to washing in water and chlorine. Both concentrations of CAR and TC, and 0.75% EUG decreased Salmonella counts on tomatoes by ~ 6.0 log CFU/ml at 1 min. Both concentrations of BR decreased the pathogen on tomatoes to undetectable levels at 3 min of exposure. Washing of tomatoes in deionized water and chlorine for 3 min reduced Salmonella by ca. 2.0 and 4.0 log CFU/ml, respectively. No Salmonella was detected in the wash water containing the plant molecules or chlorine, whereas a substantial population of the pathogen survived in the control wash water. Moreover, none of the dipping treatments had any effect on the red color of tomatoes (P > 0.05). Results indicate that CAR, TC, EUG and BR could effectively be used to kill Salmonella on tomatoes, but additional studies on sensory and quality characteristics of tomatoes treated with plant molecules are warranted.     

Enhanced elimination of Salmonella Typhimurium and Campylobacter jejuni on chicken skin by sequential exposure to ultrasound and peroxyacetic acid

The present study investigated the effects of combined ultrasound (37 kHz, 380 W for 5 min) and peroxyacetic acid (PAA; 50–200 ppm) treatment on the reduction of Salmonella Typhimurium and Campylobacter jejuni on chicken skin. Ultrasound was not sufficient to inactivate S. Typhimurium (0.48 log CFU/g reduction) or C. jejuni (0.25 log CFU/g reduction), whereas PAA significantly (p < .05) reduced S. Typhimurium (0.93–1.59 log CFU/g reduction) and C. jejuni (0.77–1.52 log CFU/g reduction). However, maximum reductions of 2.21 and 2.08 log CFU/g were observed for S. Typhimurium and C. jejuni, respectively, for combined treatment with 5 min of ultrasound and 200 ppm PAA. Our results indicate that a combination of ultrasound treatment for 5 min and 200 ppm PAA was more effective in reducing S. Typhimurium and C. jejuni compared to the individual treatments, without significantly affecting the color or texture of the chicken skin, thus, demonstrating its potential to increase the microbial safety during poultry processing.     

Development of multiplex loop-mediated isothermal amplification-RFLP (mLAMP-RFLP) to detect Salmonella spp. and Shigella spp. in milk

A multiplex loop-mediated isothermal amplification-RFLP (mLAMP-RFLP) was developed and validated for simultaneous detection of Salmonella strains and Shigella strains in milk. In this system, two sets of LAMP primers were designed to specifically target invA of Salmonella spp. and ipaH of Shigella spp. Under isothermal conditions at 63 °C, ladder pattern of DNA bands could be amplified within 60 min in the presence of genomic DNAs of Salmonella strains and Shigella strains, which could be distinguished between Salmonella spp. and Shigella spp. simultaneously based on the different ladder pattern of DNA bands and subsequent restriction enzyme analysis. The overall analysis time was approximately 20 h including the enrichment of the bacterial cells, which greatly saved detection time. The sensitivity of mLAMP was found to be 100 fg DNA/tube with genomic DNAs of Salmonella strains and Shigella strains, comparatively, multiplex PCR was 1 pg DNA/tube. The mLAMP allowed the detection of milk sample artificially contaminated by Salmonella strains and Shigella strains at initial inoculation levels of approximate 5 CFU/10 mL. In conclusion, the mLAMP described here can potentially facilitate simultaneous monitoring of Salmonella and Shigella in a large number of food samples, which could be used as a primary screening method and as a supplement to classical detection method.     

Microbiological changes in mayonnaise-based salads during storage

Within 6 h of manufacture of coleslaw, Florida, potato, Spanish and vegetable salads the concentration of acetic acid in the mayonnaise component decreased by absorption into the plant tissue, and the pH increased. Except in Spanish salad, where the concentration of acetic acid remained at an inhibitory level, these changes allowed the growth of microorganisms in salads stored at 10°C, but not at 5°C, and emphasized the need for careful control of temperature during the distribution and sale of these products.     

Inactivation of Salmonella enterica serovar Typhimurium and Quality Maintenance of Cherry Tomatoes Treated with Gaseous Essential Oils

The antimicrobial activity of the essential oils (EOs) from cinnamon bark, oregano, mustard, and of their major components cinnamaldehyde, carvacrol, and allyl isothiocyanate (AIT) was evaluated as a gaseous treatment to reduce Salmonella enterica serovar Typhimurium in vitro and on tomatoes. In vitro tests showed that mustard EO and AIT had the greatest inhibition of Salmonella, followed by cinnamon EO and cinnamaldehyde, while oregano and carvacrol showed the least inhibition. Scanning electron microscopy images of S. Typhimurium on tomatoes suggest that the EOs and their major components damaged the bacteria, and the damage was more obvious after posttreatment storage at 10 °C for 4 and 7 d. Salmonella on inoculated tomatoes was reduced by more than 5 log colony forming units (CFU)/g by mustard EO and AIT, by 4.56 and 3.79 log CFU/g following cinnamon EO and cinnamaldehyde treatments, respectively, and 1.54 and 3.37 log CFU/g after oregano EO and carvacrol treatments, respectively. Mustard EO and AIT induced discoloration, softening, and loss of the vitamin C and lycopene during 21 d of storage at 10 °C, while treatment with cinnamon EO and cinnamaldehyde did not result in significant changes in tomato quality. Tomatoes treated with oregano EO had better quality than nontreated samples after storage. Therefore, treatment with cinnamon and oregano EO and their major components appeared to be feasible for inactivation of Salmonella on tomatoes and maintaining quality.     

Growth potential of Listeria monocytogenes strains in mixed ready-to-eat salads

In this study, a microbiological challenge test in three artificially contaminated retail mixed mayonnaise-based ready-to-eat salads stored at refrigerator temperatures (3 °C and 7 °C) for 48 h was carried out. Shrimp-tomato salad, smoked ham salad and garlic cheese salad were separately contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes, Enterobacteriaceae, staphylococci and total plate count (CFU/g) was determined. Listeria monocytogenes growth potential in the salads was calculated and evaluated.A significant increase in total plate count and L. monocytogenes count throughout storage of all three investigated salads was found. Enterobacteriaceae levels were high at the beginning in all salads but significantly (p < 0.05) decreased throughout the experiment depending on the temperature.All investigated L. monocytogenes strains demonstrated growth at both temperatures but expressed different growth potential. Especially garlic cheese salad and smoked ham salad were able to support the growth of Listeria. Shrimp-tomato salad supported growth the least. The growth potential increased with the increasing temperature and exceeded 0.5 log₁₀ CFU/g in many cases. If the potential for growth is > 0.5 log₁₀ CFU/g, food products can potentially endanger human health. Reference strain (ATCC 7644) showed the least growth potential almost in all cases in comparison with strains isolated from frozen pollock loins and from thermally treated specialty sausage containing preservatives. To eliminate the occurrence of microbiological risks, the shelf-life of the studied salads was estimated.     

Development of a rapid FLISA detection of Salmonella spp. based on CdTe/ZnS quantum dots

Salmonella pathogen is old and difficult to control in food safety. The study was aimed to develop a sensitive and rapid CdTe/ZnS quantum dots (QDs) mediated fluorescence-linked immunosorbent assay (FLISA) of Salmonella spp. The optical properties and structure of the CdTe/ZnS QDs were characterized by UV–Vis absorption spectroscopy and transmission electron microscopy. The emission peak wavelength is 575 nm. The CdTe/ZnS QDs-labeled secondary antibody (goat anti-rabbit IgG) was formed by biotin-avidin system. The detection limits of S. Enteritidis and artificial simulated samples are 1.0 × 10³ CFU/ml and 1.78 × 10³ CFU/ml, respectively. The study of FLISA stability shows that the antibody with QDs had very good activity when it was stored in the dark at 4°C for at least 35 days. The FLISA provides a new and easy-operated method for the rapid detection of Salmonella spp. and has broad application in food safety.     

Effect of Cold Atmospheric Plasma processing on quality and shelf-life of ready-to-eat rocket leafy salad

The effect of Cold Atmospheric Plasma (CAP) on ready-to-eat (RTE), fresh cut, leafy rocket salad (ready-to-eat arugula leaves packed in pouches of 125 g) was investigated, aiming at quality retention and shelf-life extension. CAP was generated via a surface dielectric barrier discharge source and its efficiency on rocket leaves was evaluated at different processing times through microbial, texture, pH value and colour analyses. A reduction of 0.57 to 1.02 log CFU/g was observed for the total microbial load after processing times ranging from 5 to 20 min, respectively. A CAP processing time of 10 min was considered as optimum, for a sufficient reduction of the microbial load while maintaining colour and texture. The shelf-life of the optimum CAP-processed rocket stored at 2-9 °C was estimated through analysis of specific quality parameters. Pseudomonas spp. growth (higher count of approximately 7.0 log CFU/g) was considered to be the dominant deterioration factor. The shelf-life of the CAP-treated leafy rocket salad was estimated as 116, 84 and 55 h compared to 63, 57 and 37 h for the control samples after storage at 2, 5 and 9 °C, respectively.Industrial relevanceSpoilage of fresh-cut vegetables due to microbial growth has a significant economic impact causing food waste by reducing the shelf-life of the products and posing a risk for the public health through possible foodborne illnesses. As a result, there is a real need to seek for alternative methods for preservation of fresh produce. Cold Atmospheric Plasma technology could potentially be applied for microbial load reduction of leafy salads. The proposed protocol along with the device used for Surface Dielectric Barrier Discharge treatment, could be a potential solution for extending the shelf-life of significantly perishable fresh produce.     

Fate of Escherichia coli O157:H7 in coleslaw during storage

An outbreak of Escherichia coli O157:H7 infection associated with the consumption of coleslaw in several units of a restaurant chain prompted a study to determine the fate of the pathogen in two commercial coleslaw preparations (pH 4.3 and 4.5) held at 4, 11, and 21 degrees C for 3 days. At an initial population of 5.3 log10 CFU/g of coleslaw, E. coli O157:H7 did not grow in either coleslaw stored at the three temperatures. Rather, the population of E. coli O157:H7 decreased by 0.1 to 0.5 log10 CFU/g within 3 days. The greatest reduction (0.4 and 0.5 log10 CFU/g) in population occurred at 21 degrees C, whereas only slight decreases (0.1 to 0.2 log10 CFU/g) occurred at 4 and 11 degrees C. A pH of 4.3 to 4.5 of coleslaw had little effect on reducing E. coli O157:H7 populations. Results suggest that the tolerance of E. coli O157:H7 to acid pH, not temperature abuse, is a major factor influencing the pathogen's fate in restaurant-prepared coleslaw.     

Efficacy of Aqueous and Alcohol-Based Quaternary Ammonium Sanitizers for Reducing Salmonella in Dusts Generated in Almond Hulling and Shelling Facilities

ABSTRACT: Large volumes of fine particulate matter or “dust” (soil, hulls, and shells) generated when hulls and shells are removed from almond kernels complicate cleaning and sanitation procedures in the huller-sheller (HS) environment. This study evaluated the efficacy of 3 aqueous quaternary ammonium sanitizers (AQuats) and an isopropyl alcohol-based quaternary ammonium sanitizer (IPAQuat) for reducing Salmonella in dust collected from 2 HS facilities. Dust (1 g) was thoroughly mixed with 1 to 2 mL of inoculum (1 to 5 log CFU/g) before adding 1 to 7 mL of water, an AQuat (200 or 1000 ppm), or IPAQuat (200 ppm, 58.6% isopropyl alcohol) and incubated at 15 and 30 °C for up to 21 d. At either 15 or 30 °C increases in Salmonella populations in the dust were not significantly different following addition of either water or AQuats. No significant differences were observed upon water or AQuat addition, either among the 3 AQuats tested, the concentration or volume of AQuat, or the initial level of Salmonella. When IPAQuat was added to dust inoculated at 1 to 7 log CFU/g, Salmonella levels were reduced to less than 1.3 log CFU/g after treatment and after incubation at 30 °C for 48 h. IPAQuat was an effective sanitizer compared to the AQuats, even in the presence of high levels of organic material. Recent large-scale outbreaks of salmonellosis with low-moisture foods have increased concerns regarding their safety. Little research or guidance is available on appropriate cleaning and sanitation programs for these food types. This research is focused on an evaluation of sanitation options for low-moisture foods, in particular almonds. The information should be applicable and useful to the nut industry and to other low-moisture foods. Practical Application: Recent large-scale outbreaks of salmonellosis with low-moisture foods have increased concerns regarding their safety. Little research or guidance is available on appropriate cleaning and sanitation programs for these food types. This research is focused on an evaluation of sanitation options for low-moisture foods, in particular almonds. The information should be applicable and useful to the nut industry and to other low-moisture foods.     

Effect of Product Dimensions and Surface Browning Method on Salmonella Contamination in Frozen,Surface‐Browned,Breaded Chicken Products Treated with Antimicrobials

Not‐ready‐to‐eat breaded chicken products formulated with antimicrobial ingredients were tested for the effect of sample dimensions, surface browning method and final internal sample temperature on inoculated Salmonella populations. Fresh chicken breast meat portions (5 × 5 × 5 cm), inoculated with Salmonella (7‐strain mixture; 5 log CFU/g), were mixed with (5% v/w total moisture enhancement) (i) distilled water (control), (ii) caprylic acid (CAA; 0.0625%) and carvacrol (CAR; 0.075%), (iii) CAA (0.25%) and ε‐polylysine (POL; 0.5%), (iv) CAR (0.15%) and POL (0.5%), or (v) CAA (0.0625%), CAR (0.075%) and POL (0.5%). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments. The mixtures were then ground and formed into 9 × 5 × 3 cm (150 g) or 9 × 2.5 × 2 cm (50 g) portions. The products were breaded, browned in (i) an oven (208 °C, 15 min) or (ii) deep fryer (190 °C, 15 s), packaged, and stored at –20 °C (8 d). Overall, maximum internal temperatures of 62.4 ± 4.0 °C (9 × 2.5 × 2 cm) and 46.0 ± 3.0 °C (9 × 5 × 3 cm) were reached in oven‐browned samples, and 35.0 ± 1.1 °C (9 × 2.5 × 2 cm) and 31.7 ± 2.6 °C (9 × 5 × 3 cm) in fryer‐browned samples. Irrespective of formulation treatment, total (after frozen storage) reductions of Salmonella were greater (P < 0.05) for 9 × 2.5 × 2 cm oven‐browned samples (3.8 to at least 4.6 log CFU/g) than for 9 × 5 × 3 cm oven‐browned samples (0.7 to 2.5 log CFU/g). Product dimensions did not (P ≥ 0.05) affect Salmonella reductions (0.6 to 2.8 log CFU/g) in fryer‐browned samples. All antimicrobial treatments reduced Salmonella to undetectable levels (<0.3 log CFU/g) in oven‐browned 9 × 2.5 × 2 cm samples. Overall, the data may be useful for the selection of antimicrobials, product dimensions, and surface browning methods for reducing Salmonella contamination.     

Effect of carvacrol and thymol on Salmonella spp. biofilms on polypropylene

The present study evaluated the effects of carvacrol and thymol against Salmonella spp. biofilm on polypropylene. The efficacy of the compounds was assessed by quantifying Salmonella spp. cells during and after biofilm formation on polypropylene and performing scanning electron microscopy. During biofilm formation, carvacrol and thymol, at subinhibitory concentrations, reduced bacterial counts about 1–2 log, while established Salmonella spp. biofilms were reduced about 1–5 log by carvacrol and thymol, at MIC or 2× MIC. The greatest reduction in carvacrol‐treated biofilms, about 5 log, was observed with 156 and 312 μg mL^?1 (MIC and 2× MIC) in established Salmonella Typhimurium ATCC 14028 biofilms. Thymol showed the greatest reduction, about 4 log, at 624 μg mL^?1 (2× MIC) against mature Salmonella Enteritidis biofilm. Carvacrol and thymol reduced the number of Salmonella spp. cells on polypropylene, suggesting their potential for the control of Salmonella spp. biofilms.     

The antimicrobial properties of chitosan in mayonnaise and mayonnaise-based shrimp salads

The potential for using chitosan glutamate as a natural food preservative in mayonnaise and mayonnaise-based shrimp salad was investigated. Mayonnaise containing 3 g/liter of chitosan combined with acetic acid (0.16%) or lemon juice (1.2 and 2.6%) was inoculated with log 5 to 6 CFU/g of Salmonella Enteritidis, Zygosaccharomyces bailii, or Lactobacillus fructivorans and stored at 5 and 25 degrees C for 8 days. In mayonnaise containing chitosan and 0.16% acetic acid, 5 log CFU/g of L. fructivorans were inactivated, and numbers remained below the sensitivity limit of the plate counting technique for the duration of the experiment. Z. bailii counts were also reduced by approximately 1 to 2 log CFU/g within the first day of incubation at 25 degrees C, but this was followed by growth on subsequent days, giving an overall growth delay of 2 days. No differences in counts of Z. bailii in mayonnaise stored at 5 degrees C or of Salmonella Enteritidis stored at either temperature were observed. In mayonnaise containing lemon juice at both 1.2 and 2.6%, no substantial differences were observed between the controls and the samples containing chitosan. In shrimp salads stored at 5 degrees C, the presence of a coating of chitosan (9 mg/g of shrimp) inhibited growth of the spoilage flora from approximately log 8 CFU/g in the controls to log 4 CFU/g throughout 4 weeks. However, at 25 degrees C, chitosan was ineffective as a preservative. The results demonstrated that chitosan may be useful as a preservative when combined with acetic acid and chill storage in specific food applications.     

Listeria monocytogenes Inhibition in Refrigerated Vacuum Packaged Turkey Bologna by Chemical Additives

Sliced cooked turkey bologna with various additive formulations was surface-inoculated with Listeria monocytogenes (2.06–2.75 log CFU/g), vacuum packaged, and stored at 4°C. Sodium acetate was most inhibitory against growth of L. monocytogenes, followed by sodium lactate and potassium sorbate, while sodium bicarbonate allowed a maximum net growth of 6.78 log CFU/g, not significantly different (p>0.05) from the control (6.43 log CFU/g). Addition of 0.5% sodium acetate, 2.0% sodium lactate, or 0.26% potassium sorbate may significantly (p<0.05) decrease growth of L. monocytogenes in refrigerated turkey bologna surface-inoculated after thermal processing and slicing.