Antimicrobial Effects of Nisin,Essential Oil,and γ‐Irradiation Treatments against High Load of Salmonella typhimurium on Mini‐carrots

This study aimed at using essential oil (EO) alone or combined EO with nisin and γ‐irradiation to control Salmonella Typhimurium during the refrigerated storage of mini‐carrots. Peeled mini‐carrots were inoculated with S. Typhimurium at a final concentration of approximately 7 log CFU/g. Inoculated samples were coated by 5 different coating solutions: (i) nisin solution at final concentration of 10³ IU/mL; (ii) mountain savory EO solution at 0.35%; (iii) carvacrol solution at 0.35%; (iv) mountain savory EO at 0.35% plus nisin solution of 10³ IU/mL; or (v) carvacrol at 0.35% plus nisin solution of 10³ IU/mL. Coated mini‐carrots were then irradiated at 0.5 or 1.0 kGy and compared to an unirradiated control sample. Samples were kept at 4 °C and microbial analyses were conducted at days 1, 3, 6, and 9. The results showed that mini‐carrots coated by carvacrol plus nisin solution or mountain savory EO plus nisin solution in combination with irradiation at 1.0 kGy completely eliminated S. Typhimurium to under the detection limit during the storage. Thus, the combined treatments using carvacrol plus nisin or mountain savory EO plus nisin coating solution and irradiation at 1.0 kGy could be used as an effective method for controlling S. Typhimurium in mini‐carrots.     

Inhibition of Listeria monocytogenes by Nisin Combined with Grape Seed Extract or Green Tea Extract in Soy Protein Film Coated on Turkey Frankfurters

The objective of this study was to evaluate the inhibitory effect of grape seed extract (GSE), green tea extract (GTE), nisin and their combinations (nisin with either GSE or GTE) against Listeria monocytogenes. The inhibitory effect of these natural compounds was evaluated in phosphate buffer solution (PBS) medium containing approximately 10⁹ colony‐forming units (CFU/mL) of L. monocytogenes. The effectiveness of these compounds in a meat model system was evaluated by surface inoculation (approximately 10⁶ CFU/g) of L. monocytogenes onto turkey frankfurters. The inoculated frankfurters were dipped into soy protein film‐forming solutions with and without the addition of antimicrobial agents (GSE 1% or GTE 1% or nisin 10000 IU or combinations). Samples were stored at either 4 °C or 10 °C. The inhibitory effects of edible coatings were evaluated on a weekly basis for 28 d. The greatest inhibitory effect was observed in the PBS medium containing GSE (1%) and nisin (10000 IU/mL), which caused a 9‐log cycle reduction of L. monocytogenes population after 3 h incubation at 37 °C. In the meat system, the L. monocytogenes population (7.1 CFU/g) was decreased by more than 2 log cycle after 28 d at 4 °C and 10 °C, in the samples containing nisin (10000 IU) combined with either GSE (1%) or GTE (1%). This research has demonstrated that the use of an edible film coating containing both nisin and natural extracts is a promising means of controlling the growth and recontamination of L. monocytogenes on ready‐to‐eat meat products.     

The antimicrobial effect of thyme essential oil, nisin and their combination against Escherichia coli O157:H7 in minced beef during refrigerated storage

The antimicrobial effect of thyme essential oil (EO) at supplementation levels of 0.3%, 0.6% or 0.9%, nisin at 500 or 1000 IU/g, and their combination, on Escherichia coli O157:H7 was examined in both tryptic soy broth (TSB) and minced beef meat. EO at 0.3% possessed a weak antibacterial activity against the pathogen in TSB, whereas at 0.9% showed unacceptable organoleptic properties in minced meat. Thus, only the level of 0.6% of EO was further examined against the pathogens in minced meat. Treatment of minced beef meat with EO at 0.6% showed an inhibitory activity against E. coli O157:H7 during storage at 10 °C, but not at 4 °C. Treatment of minced beef meat or TSB with nisin at 500 or 1000 IU/g did not show any antibacterial activity against E. coli O157:H7. The combination of EO at 0.6% and nisin at 500 or 1000 IU/g showed an additive effect against the pathogen, which was higher during storage at 10 °C than at 4 °C.     

Inhibition of Listeria innocua in hummus by a combination of nisin and citric acid

The effect of nisin or citric acid or combinations of these two inhibitors on the inactivation of a cocktail of three Listeria innocua strains was investigated in a model brain heart infusion (BHI) broth and hummus (chickpea dip). In BHI broth, citric acid had a limited ability to inhibit L. innocua growth. Nisin initially reduced L. innocua concentrations by about 3 log cycles; however, L. innocua reached concentrations similar to those of the control after 5 days at 22 degrees C. In combination, the effects of 500 IU/ml nisin and 0.2% citric acid were synergistic and resulted in complete elimination of L. innocua in the BHI broth. The inhibition of L. innocua by nisin (500 or 1,000 IU/g), citric acid (0.1, 0.2, or 0.3%), or their combinations also was evaluated in hummus. Citric acid alone did not affect L. innocua growth or the aerobic bacterial plate count. A combination of 1,000 IU/g nisin and 0.3% citric acid was somewhat effective (approximately 1.5-log reduction) in controlling the concentration of L. innocua and the aerobic plate count for up to 6 days. This combination also may be useful, in addition to proper hygienic practices, for minimizing the growth of the pathogen Listeria monocytogenes in hummus.     

Antimicrobial Activity of Citric, Lactic, Malic, or Tartaric Acids and Nisin-incorporated Soy Protein Film Against Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella gaminara

ABSTRACT: We studied the effectiveness of partial replacement of glycerol with citric, lactic, malic, and tartaric acids on the antimicrobial activities of nisin (205 IU/g protein)-incorporated soy protein film against Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella gaminara. S. gaminara inoculated into 2.6% malic acid-incorporated films and lactic acid-incorporated films with nisin (5.7 and 3.4 log number colony-forming units (CFU)/mL, respectively) and without nisin (3.2 and 3.0 log number CFU/mL, respectively) had fewer survivors than HCl-incorporated film with and without nisin (8.6 and 7.9 log number CFU/mL, respectively). Malic acid (2.6%)-incorporated soy protein film had the fewest survivors of L. monocytogenes, S. gaminara , and E. coli O157:H7 (5.5, 3.0, and 6.8 log number CFU/mL, respectively) and has the potential to inhibit a wide spectrum of microbes in product application.     

Inhibition of Listeria monocytogenes and Salmonella by Combinations of Oriental Mustard,Malic Acid,and EDTA

The antimicrobial activities of oriental mustard extract alone or combined with malic acid and EDTA were investigated against Salmonella spp. or Listeria monocytogenes at different temperatures. Five strain Salmonella or L. monocytogenes cocktails were separately inoculated in Brain Heart Infusion broth containing 0.5% (w/v) aqueous oriental mustard extract and incubated at 4 °C to 21 °C for 21 d. For inhibitor combination tests, Salmonella Typhimurium 02:8423 and L. monocytogenes 2–243 were individually inoculated in Mueller Hinton broth containing the mustard extract with either or both 0.2% (w/v) malic acid and 0.2% (w/v) EDTA and incubated at 10 °C or 21 °C for 10 to 14 d. Mustard extract inhibited growth of the L. monocytogenes cocktail at 4 °C up to 21 d (2.3 log₁₀ CFU/mL inhibition) or at 10 °C for 7 d (2.4 log₁₀ CFU/mL inhibition). Salmonella spp. viability was slightly, but significantly reduced by mustard extract at 4 °C by 21 d. Although hydrolysis of sinigrin in mustard extract by both pathogens was 2 to 6 times higher at 21 °C than at 4 °C to 10 °C, mustard was not inhibitory at 21 °C, perhaps because of the instability of its hydrolysis product (allyl isothiocyanate). At 21 °C, additive inhibitory effects of mustard extract with EDTA or malic acid led to undetectable levels of S. Typhimurium and L. monocytogenes by 7 d and 10 d, respectively. At 10 °C, S. Typhimurium was similarly susceptible, but combinations of antimicrobials were not more inhibitory to L. monocytogenes than the individual agents.     

Evaluation of overhead spray-applied sanitizers for the reduction of Salmonella on tomato surfaces

Abstract: Efficacy of sanitizers in an overhead spray and brush roller system was examined for reducing Salmonella on unwaxed, mature green tomatoes. Surface inoculated tomatoes were treated in the overhead spray system for 5, 15, 30, and 60 s. A sodium hypochlorite (NaOCl) study tested NaOCl (25, 50, and 100 mg/L) against a water control. A sanitizer study examined NaOCl (100 mg/L), chlorine dioxide (ClO₂; 5 mg/L), peroxyacetic acid (PAA; 80 mg/L), and water. The overhead spray system was also compared to a scale‐model flume. All NaOCl concentrations were significantly more effective at removing Salmonella than water and achieved at least a 3‐log₁₀ CFU/mL reduction at different treatment times (P < 0.05). NaOCl (100 mg/L) achieved a 4 ± 1.8 log₁₀ CFU/mL reduction at 15 s. In the sanitizer study, NaOCl, ClO₂, and PAA achieved at least a 3‐log₁₀ CFU/mL reduction at 15 s and between 3.9 and 5.5 log₁₀ CFU/mL reductions at 30 to 60 s. NaOCl (100 mg/L) in the overhead spray system significantly reduced more Salmonella than in the flume at 15 to 60 s. NaOCl flume treatment only reached a 1.3 ± 1.1 log₁₀ CFU/mL reduction at 15 s. Results of this study demonstrate the ability of sanitizers in the laboratory model overhead spray system to reduce Salmonella on tomato surfaces. An overhead spray system could be implemented instead of flumes to achieve higher pathogen reduction with less water and sanitizer use, thereby lowering packing costs. Practical Application: The use of a non‐recirculating, overhead spray brush roller system could offer a cost effective and efficacious way of washing tomatoes. The use large communal dump tanks in tomato processing has been suspected as a source of contamination in the tomato processing process. If effective, the brush roller system could augment or possible replace currently used dump tanks.     

Evaluation of Antibacterial Activity of Whey Protein Isolate Coating Incorporated with Nisin,Grape Seed Extract,Malic Acid,and EDTA on a Turkey Frankfurter System

ABSTRACT: The effectiveness of whey protein isolate (WPI) coatings incorporated with grape seed extract (GSE), nisin (N), malic acid (MA), and ethylenediamine tetraacetic acid (EDTA) and their combinations to inhibit the growth of Listeria monocytogenes, E. coli O157:H7, and Salmonella typhimurium were evaluated in a turkey frankfurter system through surface inoculation (approximately 10⁶ CFU/g) of pathogens. The inoculated frankfurters were dipped into WPI film forming solutions both with and without the addition of antimicrobial agents (GSE, MA, or N and EDTA, or combinations). Samples were stored at 4 °C for 28 d. The L. monocytogenes population (5.5 log/g) decreased to 2.3 log/g after 28 d at 4 °C in the samples containing nisin (6000 IU/g) combined with GSE (0.5%) and MA (1.0%). The S. typhimurium population (6.0 log/g) was decreased to approximately 1 log cycles after 28 d at 4 °C in the samples coated with WPI containing a combination of N, MA, GSE, and EDTA. The E. coli O157:H7 population (6.15 log/g) was decreased by 4.6 log cycles after 28 d in samples containing WPI coating incorporated with N, MA, and EDTA. These findings demonstrated that the use of an edible film coating containing nisin, organic acids, and natural extracts is a promising means of controlling the growth and recontamination of L. monocytogenes, S. typhimurium, and E. coli O157:H7 in ready‐to‐eat poultry products.     

Antimicrobial Effects of Lactoferrin, Lysozyme, and the Lactoperoxidase System and Edible Whey Protein Films Incorporating the Lactoperoxidase System Against Salmonella enterica and Escherichia coli O157:H7

Lactoferrin (LF), lysozyme (LZ), the lactoperoxidase system (LPOS), and edible whey protein isolate (WPI) films incorporating LPOS were studied for inhibition of Salmonella enterica and Escherichia coli O157:H7. Antimicrobial effects of LF (5 to 40 mg/mL), LZ (1 to 20 mg/mL), and LPOS (0.5% to 5.0% [w/v] [0.03–.25 g/g, dry basis]) were examined by measuring turbidity of antimicrobial‐containing media after inoculation and by examining cell inhibition by WPI films incorporating LPOS (LPOS‐WPI films) on an agar recovery medium. Elastic modulus (EM), tensile strength (TS), percent elongation (%E), oxygen permeability (OP), and Hunter L, a and b of WPI films incorporating 0.03 to 0.25 g/g of LPOS were compared with those of plain WPI films without LPOS. The growth of S. enterica and E. coli O157:H7 (4 log colony‐forming units [CFU]/mL) in tryptic soy broth (TSB) was not prevented by LF at ≥20 and ≥40 mg/mL, respectively. S. enterica and E. coli O157:H7 in TSB were not inhibited by LZ at ≥ 6 and ≥ 20 mg/mL, respectively. LPOS at concentrations of 2.75% (w/v) and 1.0% (w/v) reduced S. enterica and E. coli O157:H7 to below the limit of detection (1 CFU/mL) in TSB, respectively. LPOS‐WPI films (0.15 g/g) completely inhibited S. enterica and E. coli O157:H7 (4 log CFU/cm²), inoculated either onto agar before placing the film disc or onto top of the film disc. Incorporation of 0.25 g/g of LPOS decreased EM, TS, and %E. The oxygen barrier property of WPI films was improved with the incorporation of LPOS at 0.15 to 0.25 g/g.     

Salmonella sensitivity to sodium hypochlorite and citric acid in washing water of lettuce residues

Salmonella spp. is one of the main lettuce pathogens and should be inactivated during the disinfection of these vegetables before consumption. In minimally processed vegetable industries, residues of organic matter can prevent the inactivation of this pathogen by disinfectants. The objective of the present work was to evaluate the inactivation of Salmonella isolated from organic lettuce to sodium hypochlorite (25 and 50 ppm) and citric acid (0.5 and 1%) in washing water added with lettuce residues. To do so, a washing water with lettuce residues was elaborated, and Salmonella was added in the order of 10⁶ CFU/ml. Thereafter, each sanitizer was added separately to evaluate its effect on reducing Salmonella counts. After 1, 2, 3, 4, 5, 10, and 15 min of contact with the sanitizers, serial dilutions using neutralizer (0.5% sodium thiosulfate) were performed and each dilution was sown in Xylose-Lysine-Desoxycholate medium. Total aerobic mesophilic counts of wash water with lettuce residues before testing (without Salmonella) and after 15 min of exposure to each sanitizer (with Salmonella) were also performed. In addition, the free chlorine still present in the samples after the contact of sodium hypochlorite with lettuce residues for 15 min. The results demonstrated that 50 and 25 ppm sodium hypochlorite could reduce 6 log CFU/ml of Salmonella in 1 and 3 min of contact, respectively, while 0.5 and 1% citric acid was able to reduce 1.26 and 1.74 log CFU/ml respectively from the same microorganism within 15 min of contact. The total aerobic mesophilic counts of the wash water before being tested were, on average, 1.5 log CFU/ml. After addition of Salmonella, with 15 min of contact with the sanitizer, the results of total counts showed the same magnitude as the Salmonella counts. Organic matter may have reacted with the free chlorine present, reducing chlorine concentrations, since values of 30.4 ppm were observed when the initial concentration should be 50 and 17.1 ppm when the initial concentration should be 25 ppm. Based on the results, sodium hypochlorite demonstrated a greater microbial reduction capacity in wash water with lettuce residues, indicating that it is more appropriate to avoid cross-contamination between batches during sanitation of lettuce in washing tanks.     

Biodegradable polylactic acid polymer with nisin for use in antimicrobial food packaging

ABSTRACT:  Biodegradable polylactic acid (PLA) polymer was evaluated for its application as a material for antimicrobial food packaging. PLA films were incorporated with nisin to for control of foodborne pathogens. Antimicrobial activity of PLA/nisin films against Listeria monocytogenes , Escherichia coli O157:H7, and Salmonella Enteritidis were evaluated in culture media and liquid foods (orange juice and liquid egg white). Scanned electron micrograph and confocal laser microscopy revealed that nisin particles were evenly distributed in PLA polymer matrix on the surface and inside of the PLA/nisin films. PLA/nisin significantly inhibited growth of L . monocytogenes in culture medium and liquid egg white. The greatest inhibition occurred at 24 h when the cell counts of L. monocytogenes in the PLA/nisin samples were 4.5 log CFU/mL less than the controls. PLA/nisin reduced the cell population of E. coli O157:H7 in orange juice from 7.5 to 3.5 log at 72 h whereas the control remained at about 6 log CFU/mL. PLA/nisin treatment resulted in a 2 log reduction of S. Enteritidis in liquid egg white at 24 °C. After 21 d at 4 °C the S. Enteritidis population from PLA/nisin treated liquid egg white (3.5 log CFU/mL) was significantly less than the control (6.8 log CFU/mL). E. coli O157:H7 in orange juice was more sensitive to PLA/nisin treatments than in culture medium. The results of this research demonstrated the retention of nisin activity when incorporated into the PLA polymer and its antimicrobial effectiveness against foodborne pathogens. The combination of a biopolymer and natural bacteriocin has potential for use in antimicrobial food packaging.     

Inhibition of Listeria monocytogenes by food antimicrobials applied singly and in combination

Abstract: Combining food antimicrobials can enhance inhibition of Listeria monocytogenes in ready-to-eat (RTE) meats. A broth dilution assay was used to compare the inhibition of L. monocytogenes resulting from exposure to nisin, acidic calcium sulfate, ɛ-poly-L-lysine, and lauric arginate ester applied singly and in combination. Minimum inhibitory concentrations (MICs) were the lowest concentrations of single antimicrobials producing inhibition following 24 h incubation at 35 °C. Minimum bactericidal concentrations (MBCs) were the lowest concentrations that decreased populations by ≥3.0 log₁₀ CFU/mL. Combinations of nisin with acidic calcium sulfate, nisin with lauric arginate ester, and ɛ-poly-L-lysine with acidic calcium sulfate were prepared using a checkerboard assay to determine optimal inhibitory combinations (OICs). Fractional inhibitory concentrations (FICs) were calculated from OICs and were used to create FIC indices (FIC_Is) and isobolograms to classify combinations as synergistic (FIC_I < 1.00), additive/indifferent (FIC_I= 1.00), or antagonistic (FIC_I > 1.00). MIC values for nisin ranged from 3.13 to 6.25 μg/g with MBC values at 6.25 μg/g for all strains except for Natl. Animal Disease Center (NADC) 2045. MIC values for ɛ-poly-L-lysine ranged from 6.25 to 12.50 μg/g with MBCs from 12.50 to 25.00 μg/g. Lauric arginate ester at 12.50 μg/g was the MIC and MBC for all strains; 12.50 mL/L was the MIC and MBC for acidic calcium sulfate. Combining nisin with acidic calcium sulfate synergistically inhibited L. monocytogenes; nisin with lauric arginate ester produced additive-type inhibition, while ɛ-poly-L-lysine with acidic calcium sulfate produced antagonistic-type inhibition. Applying nisin along with acidic calcium sulfate should be further investigated for efficacy on RTE meat surfaces. Practical Application: This study demonstrates the potential for combinations of antimicrobials to result in greater pathogen inhibition as compared to the application of a single antimicrobial. The data presented in this study can aid the food industry in developing more efficient and effective application of antimicrobials. These findings should also prompt further studies validating the inhibitory effect of combinations of antimicrobials on ready-to-eat surfaces.     

Inactivation of Listeria innocua and Escherichia coli in carrot juice by combining high pressure processing,nisin, and mild thermal treatments

This study explored the effectiveness of high pressure (200–500 MPa) alone or in combination with mild thermal treatments (35 and 50 °C) and nisin (25 and 50-ppm) on the inactivation of L. innocua and E. coli in carrot juice. Processing at 500 MPa at 20 °C for 2 min without nisin resulted in 4- and 5-log CFU/mL reduction of L. innocua and E. coli, respectively while incorporating 25-ppm nisin at same pressure and temperature rendered 7-log CFU/mL reduction. There was synergism between high pressure, nisin, and heat in all treatments to inactivate both microorganisms. After a 28-d of refrigerated storage, total plate counts were <2-log CFU/mL in carrot juice treated with combination of 300 MPa and 25-ppm nisin at 35 °C. All combinations resulted in less intense use of pressure, i.e. more energy efficient, cost effective processes while attaining high quality juices. The results of this study suggest that by using selected combinations of high pressure, nisin and mild temperatures, safe, clean-label, high-quality juices can be produced.Industrial relevanceThe results from this study show a synergistic effect on the inactivation of L. innocua and E. coli in carrot juice from the combined application of HPP, nisin, and mild temperatures. By replacing the use of HPP alone by these combinations will allow the use of reduced pressures over shorter period of times to process low-acid juices, lowering energy requirements and increasing throughput. This study will aid the beverage processing industry in the development of clean label juice products with fresh-like quality attributes and using considerable less energy to conventional processing.     

The effect of EDTA and trisodium phosphate,alone and in combination with nisin,on the growth of Arcobacter butzleri in culture

Arcobacter butzleri is a common contaminant of foods of animal origin and there is increasing evidence linking the organism to human illness. This study investigated the effectiveness of ethylene diamine tetra-acetic acid (EDTA) and trisodium phosphate (TSP) alone and in combination with nisin, on the growth of A. butzleri in culture. At 1 mM, 5 mM, 10 mM and 20 mM, EDTA inhibited growth, both alone and combined with 500 IU ml⁻¹nisin, but only at 20 mM did the addition of nisin produce a statistically significant difference compared with EDTA alone (4·3 log₁₀and 5·6 log₁₀reduction respectively). Short-term simultaneous exposure with EDTA and 500 IU ml⁻¹nisin was more effective than sequential treatment on both logarithmically growing and stationary phase cells.Growth of A. butzleri was inhibited by 0·5 mM TSP with simultaneous treatment being more effective than sequential treatment. After 10 min simultaneous treatment, only at 40 mM TSP (but not at lower concentrations) was there a statistically significant difference between TSP treatment alone and TSP plus 500 IU ml⁻¹nisin (5·2 log₁₀compared with 7·7 log₁₀reduction).Thirty-minute treatment with 20 mM EDTA or 10 min with 10% TSP at 4°C, followed by incubation in the presence of 500 IU ml⁻¹nisin, resulted in no viable cells being recovered after 24 h (>99·9% cell kill) indicating that a multiple hurdle approach is the most effective method of reducing growth and survival of A. butzleri in culture.     

Hurdle Effect of Antimicrobial Activity Achieved by Time Differential Releasing of Nisin and Chitosan Hydrolysates from Bacterial Cellulose

We investigated the combined antimicrobial effect of nisin and chitosan hydrolysates (CHs) by regulating the antimicrobial reaction order of substances due to differential releasing rate from hydroxypropylmethylcellulose‐modified bacterial cellulose (HBC). The minimum inhibitory concentration of nisin against Staphylococcus aureus and that of CHs against Escherichia coli were 6 IU and 200 μg/mL, respectively. Hurdle and additive effects in antimicrobial tests were observed when nisin was used 6 h before CH treatment against S. aureus; similar effects were observed when CH was used before nisin treatment against E. coli. Simultaneously combined treatment of nisin and CHs exhibited the low antimicrobial effect. HBC was then selected as the carrier for the controlled release of nisin and CHs. A 90% inhibition in the growth of S. aureus and E. coli was achieved when 30 IU‐nisin‐containing HBC and 62.5 μg/mL‐CH‐containing HBC were used simultaneously. The controlled release of nisin and CHs by using HBC minimized the interaction between nisin and CHs as well as increased the number of microbial targets.     

The effect of nisin and garlic (Allium sativum L.) essential oil separately and in combination on the growth of Listeria monocytogenes

In the present study, the anti-listerial activity of the nisin and garlic (Allium sativum L.) essential oils (GO) alone and in combination was investigated at different temperatures (20 and 30 °C), pH (6.8, 5.6 and 4.8) and NaCl concentrations (0, 0.5, 2.5 and 4.5 g/100 mL). Minimum inhibitory concentrations (MICs) against Listeria monocytogenes were assessed for the nisin and essential oil. Furthermore, for combinations of the antimicrobials, the Differences in Population (DP) method were used to determine their effect. Both essential oil and nisin possessed considerable antimicrobial effects on the microorganism. The MICs for nisin and GO were 12.5 IU/mL and 100 μg/mL, respectively. Regardless of NaCl concentration and temperature, the anti-listerial activity of both GO and nisin was strongly influenced by pH. Moreover, at the same temperature, and regardless of pH value, the growth of the organism was also affected by increasing NaCl concentration. In combination, the DP was related strongly to the agent’s concentration and media pH. Meanwhile, among all combined systems, the effect of the combination (EC) of nisin with GO at 30 °C, pH 5.6 and 0 g/100 mL NaCl, showed significant anti-listerial activity (P ≤ 0.05).     

Attachment and Biofilm Formation by Selected Strains of Salmonella enterica and Entrohemorrhagic Escherichia coli of Fresh Produce Origin

This study compared the abilities of selected Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) strains of fresh produce origin to form biofilms on polystyrene surface and to attach to alfalfa and bean sprouts. Each of the 7 S. enterica and 4 EHEC inocula (2 mL; 10⁷ CFU/mL) was placed in 6 different broths in 24‐well polystyrene tissue culture plates at 28 °C for 1 to 7 d. Developed biofilms were quantified using the crystal violet binding assay. In a separate experiment, alfalfa and mung bean sprouts (5 g) were exposed to 25 mL inocula (10⁷ CFU/mL) of S. enterica or EHEC at 22 °C for 2 h with shaking at 40 rpm. Contaminated sprouts were thoroughly rinsed and homogenized in 0.1% peptone water, and bacteria attached to sprouts were enumerated. Biofilm mass accumulated on polystyrene surface increased with incubation time (P < 0.05). Among the microbiological media used, LB no salt (NaCl) broth better supported biofilm development (P < 0.05). Two EHEC strains formed more biofilms than the Salmonella and other two EHEC strains (P < 0.05). However, more Salmonella cells (5.66 log CFU/g) attached to sprouts than EHEC cells (3.46 log CFU/g). Both Salmonella and EHEC attached in higher numbers to mung bean, than alfalfa, sprouts (P < 0.05).     

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.     

Decontamination of Salmonella enterica Typhimurium on green onions using a new formula of sanitizer washing and pulsed UV light (PL)

Pathogenic bacteria such as Salmonella and Shigella flexneri have been linked to green onion contamination. This study was conducted to evaluate decontamination of Salmonella Typhimurium using a new formula of sanitizer washing (0.4 mg/mL thymol and five new formula sanitizers including 300 ppm H₂O₂ + 4% SDS, 2 mg/mL citric acid + 4% SDS, 0.2 mg/mL thymol + 4% SDS, 0.2 mg/mL thymol + 2 mg/mL citric acid and 0.2 mg/mL thymol + 2 mg/mL acetic acid), pulsed UV light (PL) as well as synergy between the sanitizer wash and PL. New formula sanitizers based on decontamination efficacy of single washing solutions (organic acids, hydrogen peroxide (H₂O₂), essential oil or surfactant) were applied to decontaminate spot inoculated green onions. PL, the novel technique, alone has been applied to inactivate Salmonella on both dip and spot inoculated green onions. Salmonella inactivation of PL–new formula sanitizer combinations on dip inoculated green onions was investigated for their potential synergy. As a result, for spot inoculated green onions, 0.4 mg/mL thymol individually and the five new formula sanitizers all achieved higher log reduction of Salmonella (4.5–5.3 log 10 CFU/g reduction) than the 200 ppm chlorine washing. These new formulas of sanitizer would be potential alternatives to chlorine. The 5 s dry PL (4.6 log 10 CFU/g) or 60 s wet PL treatment (3.6 log 10 CFU/g) was better or comparable as chlorine washing. The sanitizer combinations did not provide significantly higher log reduction than PL, and PL has the potential of being used in the green onion industry for decontamination purpose. For dip inoculated green onions, none of our treatment provided > 0.8 log 10 CFU/g (0.6–0.8 log 10 CFU/g) reduction of Salmonella. As a result, the PL–new formula sanitizer combinations had no or minimal synergy to inactivate Salmonella dip inoculated on green onions.     

Control of Listeria monocytogenes on the Surface of Refrigerated, Ready-to-eat Chicken Coated with Edible Zein Film Coatings Containing Nisin and/or Calcium Propionate

ABSTRACT: This study investigated the effect of nisin added to zein film coatings (Z) coated onto ready-to-eat chicken against L. monocytogenes. L. monocytogenes inoculated chicken samples were dipped into Z dissolved in propylene glycol (ZP) or ethanol (ZE), with and without added nisin (N) (1000 IU/g) and/or 1% calcium propionate (CP) then stored at 4 °C or 8 °C for 24 d. After 16 d at 4 °C the growth of L. monocytogenes (6.8 log CFU/g) was suppressed by 4.5 to 5 log CFU/g and at 2.7 log CFU/g counts were maintained at a nondetectable level from day 0 to day 24 with ZEN, ZPNCP, or ZENCP. Zein film coatings with nisin can prevent the growth of L. monocytogenes on ready-to-eat chicken.