Effect of Curing Method and Freeze-Thawing on Subsequent Growth of Listeria monocytogenes on Cold-Smoked Salmon

The presence of the foodborne pathogen Listeria monocytogenes on cold-smoked salmon is a major concern for the seafood industry. Understanding processing and postprocessing handling factors that affect the ability of this pathogen to grow on cold-smoked salmon is critical for developing effective control strategies. In this study, we investigated the effect of curing method and freeze-thawing of cold-smoked salmon on (i) physicochemical properties and (ii) subsequent growth of genetically diverse strains of L. monocytogenes (inoculated after freeze-thawing) and endogenous lactic acid bacteria. The majority of the measured physicochemical properties were unaffected by freezing and thawing. Overall, wet-cured cold-smoked salmon had higher pH, water activity, and moisture, as well as lower fat, water-phase salt, and phenolic content compared with dry-cured cold-smoked salmon. The curing method and freeze-thawing did not affect growth of endogenous lactic acid bacteria. Freeze-thawing cold-smoked salmon prior to inoculation led to pronounced growth of L. monocytogenes at 7°C. The increase in cell density between days 0 and 30 was significantly (P = 0.0078) greater for cold-smoked salmon that was frozen and thawed prior to inoculation compared with nonfrozen cold-smoked salmon. On dry-cured, freeze-thawed cold-smoked salmon, L. monocytogenes had a lag phase ranging from 3.7 ± 0.1 to 11.2 ± 1.4 days compared with salmon that was wet cured and freeze-thawed, on which L. monocytogenes began to grow within 24 h. Variation in growth among L. monocytogenes strains was also observed, indicating the significance of assessing multiple strains. Further efforts to understand the impact of processing and postprocessing handling steps of cold-smoked salmon on the growth of genetically diverse L. monocytogenes will contribute to improved challenge study designs and data. This, in turn, will likely lead to more reliable and unbiased risk assessments and control measures.     

Use of commercially available antimicrobial compounds for prevention of Listeria monocytogenes growth in ready-to-eat minced tuna and salmon roe during shelf life

Listeria monocytogenes found in minced tuna and fish roe can cause listeriosis. These products are classified in category B according to the Codex Alimentarius Commission, i.e., ready-to-eat foods in which L. monocytogenes growth can occur. We investigated the effectiveness of nisin and other commercially available antimicrobial compounds (lysozyme, ε-polylysine, and chitosan) for prevention of L. monocytogenes growth during the expected shelf life of raw minced tuna and salmon roe products. Food samples inoculated with L. monocytogenes were incubated with each antimicrobial at 10°C for 7 days or at 25°C for 12 h. Nisaplin (an antimicrobial containing nisin) effectively inhibited L. monocytogenes growth in minced tuna at 500 ppm and in salmon roe at 250 ppm within their standard shelf lives. The effective concentration of each antimicrobial was determined: 2,000 ppm for ART FRESH 50/50 (containing lysozyme) and SAN KEEPER No. 381 (containing ε-polylysine) and 10,000 ppm for SAN KEEPER K-3 (containing chitosan).     

Listeria monocytogenes inhibition by whey protein films and coatings incorporating lysozyme

The effects of whey protein isolate (WPI) films and coatings incorporating lysozyme (LZ) on the inhibition of Listeria monocytogenes both in and on microbial media, as well as on cold-smoked salmon, were studied. The antimicrobial effects of LZ were examined using various growth media by turbidity and plate counting tests. Disc-covering and disc-surface-spreading tests were also used to evaluate the effects of WPI films incorporating LZ. Smoked salmon was used as a model food to test the antimicrobial effects of WPI coatings incorporating LZ, both initially and during storage at 4 and 10 degrees C for 35 days. Tensile properties (elastic modulus, tensile strength, and percentage of elongation), oxygen permeability, and color (Hunter L, a, and b) of WPI films with and without LZ were also compared. LZ inhibited L. monocytogenes in broth and on agar media. The number of cells surviving after LZ treatments depended on the type of media. WPI films incorporating 204 mg of LZ per g of film (dry basis) inhibited the growth of a preparation of 4.4 log CFU/cm2 L. monocytogenes. WPI coatings prepared with 25 mg of LZ per g of coating solution initially inactivated more than 2.4, 4.5, and 3.0 log CFU/g of L. monocytogenes, total aerobes, and yeasts and molds in smoked salmon samples, respectively. The WPI coatings incorporating LZ efficiently retarded the growth of L. monocytogenes at both 4 and 10 degrees C. The anti-L. monocytogenes effect of LZ-WPI coating was more noticeable when the coating was applied before inoculation than when the coating was applied after inoculation. Significantly higher elastic modulus values and lower percentage of elongation and oxygen permeability values were measured with the WPI films incorporating LZ than with the plain WPI films.     

Edible chitosan films on ready-to-eat roast beef for the control of Listeria monocytogenes

The use of chitosan as an edible film was evaluated for its antimicrobial activity against Listeria monocytogenes (LM) on the surface of ready-to-eat (RTE) roast beef. L. monocytogenes, decimally diluted to give an initial inoculation of >6.50logCFU/g, was inoculated onto the surface of RTE roast beef cubes, and air-dried. The samples were dipped into chitosan (high or low molecular weights) solutions dissolved with acetic or lactic acid at 0.5% (w/v) or 1% (w/v) then bagged and refrigerated at 4 degrees C. The bacterial counts were determined on days 0, 7, 14, 21, and 28. The samples were spread plated onto modified Oxford agar plates and incubated at 37 degrees C for 48h. An initial 6.50logCFU/g of L. monocytogenes inoculated onto the surface of the non-coated RTE roast beef increased too >10logCFU/g by day 28. On day 14, L. monocytogenes counts were significantly different for all the chitosan-coated samples from the control counts by 2-3logCFU/g and remained significantly different on day 28. Our results have shown that the acetic acid chitosan coating were more effective in reducing L. monocytogenes counts than the lactic acid chitosan coating. Our study indicated that chitosan coatings could be used to control L. monocytogenes on the surface of RTE roast beef.     

Reducing levels of Listeria monocytogenes contamination on raw salmon with acidified sodium chlorite

The antimicrobial activity of acidified sodium chlorite (ASC) against Listeria monocytogenes in salmon was studied. Raw salmon (whole fish and fillets) inoculated with L. monocytogenes (10(3) CFU/cm2 or 10(4) CFU/g) were washed with ASC solution (50 ppm) for 1 min and stored at -18 degrees C for 1 month (whole salmon) or in ice for 7 days (fillets). L. monocytogenes populations were determined for whole salmon after frozen storage and for fillets on days 1, 3, 5, and 7 of storage. A wash with ASC solution followed by ASC glazing did not reduce L. monocytogenes on the skin of whole salmon during frozen storage. However, the wash resulted in an L. monocytogenes reduction of 0.5 log CFU/g for salmon fillets. The populations of L. monocytogenes in fillets increased slowly during ice storage, but the growth of these populations was retarded by ASC ice. By day 7, the populations were 0.25 log units smaller in fillets stored in ASC ice and 0.62 log units smaller in fillets that had been washed with ASC solution and stored in ASC ice than in control fillets. Treatment with ASC also reduced total plate counts (TPCs) by 0.43 log CFU/cm2 on the skin of whole salmon and by 0.31 log CFU/g in fillets. The TPCs for skin decreased during frozen storage but increased gradually for fillets stored at 5 degrees C or in ice. However, TPCs of ASC-treated samples were lower than those for controls at any point during the study. Washing with ASC solution significantly (P < 0.05) reduced TPCs on the skin of whole salmon and in fillets, as well as L. monocytogenes in fillets. The antimicrobial activity of ASC was enhanced when salmon was washed with ASC solution and stored in ASC ice.     

Inhibition of Listeria monocytogenes on bologna sausages by an antimicrobial film containing mustard extract or sinigrin

The ability of Listeria (L.) monocytogenes to convert glucosinolates into antimicrobial isothiocyanates was investigated. Mustard glucosinolates in pure (sinigrin) or extract forms (sinigrin, oriental; sinalbin, yellow mustard) were used in broth media and in a polyvinyl polyethylene glycol graft copolymer (PPG) packaging film with bologna to examine their value as antimicrobial precursors for the control of L. monocytogenes viability and extension of bologna shelf-life at 4 °C. During broth tests with deodorized (myrosinase-inactivated) mustard extracts (10 d at 20 °C) or with purified sinigrin (21 d at 20 °C) L. monocytogenes was only inhibited when exogenous myrosinase was added. None the less, the organism was able to hydrolyze almost half the pure sinigrin by 21 d in tests without added enzyme. Reductions in sinigrin levels were measured by reversed-phase liquid chromatography, and in the absence of L. monocytogenes or added myrosinase the glucosinolate was stable. When pure sinigrin, oriental or yellow mustard extracts were incorporated in PPG films containing 3, 5 and 6% (w/w) of the corresponding glucosinolate and used to package bologna inoculated with 4 log CFU/g L. monocytogenes, the pathogen became undetectable in bologna packed with the oriental mustard extract at 52 d storage and remained undetectable at 70 d. The yellow mustard extract was less inhibitory and the pure sinigrin was not antimicrobial. L. monocytogenes numbers reached >7 log CFU/g in the film and untreated controls at 17 d storage. At 35 d storage, samples packed with control film contained sufficient numbers of lactic acid bacteria (LAB) (>7 log CFU/g) to be considered spoiled, whereas treatments containing mustard or sinigrin remained <7 log CFU/g LAB for ≤ 70 d. L. monocytogenes played a key role in exerting control over its own viability in bologna by hydrolysis of the glucosinolate in the oriental mustard film, but other antimicrobials in treatments may have contributed.     

Antimicrobial chitosan-lysozyme (CL) films and coatings for enhancing microbial safety of mozzarella cheese

ABSTRACT:  This study investigated the antimicrobial activities of chitosan-lysozyme (CL) composite films and coatings against tested microorganisms inoculated onto the surface of Mozzarella cheese. CL film-forming solutions (FFS) with a pH of 4.4 to 4.5 were prepared by incorporating 0% or 60% lysozyme (per dry weight of chitosan) into chitosan FFS with or without a pH adjustment to 5.2. Sliced cheese was subjected to 3 CL package applications: film, lamination on a multilayer coextruded film, and coating. Cheese was inoculated with Listeria monocytogenes , Escherichia coli , or Pseudomonas fluorescens at 10⁴ CFU/g, or with mold and yeast at 10² CFU/g. Inoculated cheese was individually vacuum packaged and stored at 10 °C for sampling at 1, 7, and 14 d for bacteria, and at 10, 20, and 30 d for fungi. Inoculated bacteria survived but failed to multiply in untreated cheese during storage. Treated cheese received 0.43‐ to 1.25‐, 0.40‐ to 1.40‐, and 0.32- to 1.35-log reductions in E . coli , P. fluorescens , and L . monocytogenes , respectively. Incorporation of 60% lysozyme in chitosan FFS showed greater antimicrobial effect than chitosan alone on P. fluorescens and L . monocytogenes . The pH adjustment only affected the antimicrobial activity on L . monocytogenes , with lower pH (unadjusted) showing greater antimicrobial effect than pH 5.2. Mold and yeast increased to 10⁵ CFU/g in untreated cheese after 30 d storage. Growth of mold was completely inhibited in cheese packaged with CL films, while 0.24‐ to 1.90‐ and 0.06‐ to 0.50-log reductions in mold populations were observed in cheese packaged with CL-laminated films and coatings, respectively. All CL packaging applications resulted in 0.01- to 0.64-log reduction in yeast populations.     

复合抗菌膜对腊肉品质的影响

采用羧甲基纤维素(CMC)与明胶制作复合型抗菌膜用于腊肉的防腐保鲜。以膜的水蒸气透过率、膜的厚度和透光度为主要指标,对膜液的组成进行优化,以此为基础加入适量的山梨酸钾,制备出具有良好性能的复合型抗菌膜。结果表明,将CMC与明胶以质量比1:2的比例配制成质量浓度10g/L的成膜液,添加质量分数0.4%的甘油和0.08%的山梨酸钾制成复合抗菌膜,对腊肉进行涂膜保鲜够延缓腊肉的腐败速度,延长贮藏时间。     

Nisin treatment to enhance the efficacy of gamma radiation against Listeria monocytogenes on meat

Treatment of meat with gamma radiation for inactivation of foodborne pathogens might cause undesirable quality changes in the product. The objective of the present study was to use nisin for enhancing the lethality of gamma radiation against Listeria monocytogenes, so that moderate doses of radiation can effectively eliminate the pathogen on meat. Cubes of raw meat (10 g each) were inoculated with L. monocytogenes (10(7)CFU/g) and treated with nisin (10(3) IU/g), gamma radiation (0.25 to 1.5 kGy), or combinations of these treatments. Meat was analyzed for L. monocytogenes survivors immediately after treatment and during storage at 4 °C for up to 72 h. Nisin treatment alone inactivated L. monocytogenes by 1.2 log CFU/g. Gamma radiation caused dose-dependent inactivation of the pathogen. Treatment with combinations of nisin and gamma radiation resulted in an additive antimicrobial effect when inoculated meat was tested during the first 24 h and in a synergistic effect when tested after 72 h of storage at 4 °C. When L. monocytogenes was inoculated onto meat at low levels (4×10(3) CFU/g), treated with nisin (10(3) IU/g), and then irradiated (1.5 kGy) and stored at 4 °C for 72 h, the pathogen's most probable number was <0.03/g, indicating that such a combination is potentially effective in eliminating L. monocytogenes in meat.     

Studies on the pathogenesis and survival of different culture forms of Listeria monocytogenes to pulsed UV-light irradiation after exposure to mild-food processing stresses

The effects of mild conventional food-processing conditions on Listeria monocytogenes survival to pulsed UV (PUV) irradiation and virulence-associated characteristics were investigated. Specifically, this study describes the inability of 10 strains representative of 3 different culture forms or morphotypes of L. monocytogenes to adapt to normally lethal levels of PUV-irradiation after exposure to sub-lethal concentrations of salt (7.5% (w/v) NaCl for 1 h), acid (pH 5.5 for 1 h), heating (48 °C for 1 h) or PUV (UV dose 0.08 μJ/cm(2)). Findings showed that the order of increasing sensitivity of L. monocytogenes of non-adapted and stressed morphotypes to low pH (pH 3.5 for 5 h, adjusted with lactic), high salt (17.5% w/v NaCl for 5 h), heating (60 °C for 1 h) and PUV-irradiation (100 pulses at 7.2 J and 12.8 J, equivalent to UV doses of 2.7 and 8.4 μJ/cm(2) respectively) was typical wild-type smooth (S/WT), atypical filamentous rough (FR) and atypical multiple-cell-chain (MCR) variants. Exposure of L. monocytogenes cells to sub-lethal acid, salt or heating conditions resulted in similar or increased susceptibility to PUV treatments. Only prior exposure to mild heat stressing significantly enhanced invasion of Caco-2 cells, whereas subjection of L. monocytogenes cells to combined sub-lethal salt, acid and heating conditions produced the greatest reduction in invasiveness. Implications of these findings are discussed. This constitutes the first study to show that pre-exposure to mild conventional food-processing stresses enhances sensitivity of different culture morphotypes of L. monocytogenes to PUV, which is growing in popularity as an alternative or complementary approach for decontamination in the food environment.     

Adaptive growth responses of Listeria monocytogenes to acid and osmotic shifts above and across the growth boundaries

The effect of acid and osmotic shifts on the growth of Listeria monocytogenes was evaluated at 10°C. Two types of shifts were tested: (i) within the range of pH and water activity (a(w)) levels that allow growth of L. monocytogenes and (ii) after habituation at no-growth conditions back to growth-permitting conditions. A L. monocytogenes cheese isolate, with high survival capacity during cheesemaking, was inoculated (10(2) CFU/ml) in tryptic soy broth supplemented with 0.6% yeast extract at six pH levels (5.1 to 7.2; adjusted with lactic acid) and 0.5% NaCl (a(w) 0.995), or four a(w) levels (0.995 to 0.93, adjusted with 0.5 to 10.5% NaCl) at pH 7.2 and grown to early stationary phase. L. monocytogenes was then shifted (at 10(2) CFU/ml) to each of the aforementioned growth-permitting pH and a(w) levels and incubated at 10°C. Shifts from no-growth to growth-permitting conditions were carried out by transferring L. monocytogenes habituated at pH 4.9 or a(w) 0.90 (12.5% NaCl) for 1, 5, and 10 days to all pH and a(w) levels permitting growth. Reducing a(w) or pH at different levels in the range of 0.995 to 0.93 and 7.2 to 5.1, respectively, decreased the maximum specific growth rate of L. monocytogenes. The lag time of the organism increased with all osmotic downshifts, as well as by the reduction of pH to 5.1. Conversely, any type of shift within pH 5.5 to 7.2 did not markedly affect the lag times of L. monocytogenes. The longer the cells were incubated at no-growth a(w) (0.90), the faster they initiated growth subsequently, suggesting adaptation to osmotic stress. Conversely, extended habituation at pH 4.9 had the opposite effect on subsequent growth of L. monocytogenes, possibly due to cell injury. These results suggest that there is an adaptation or injury rate induced at conditions inhibiting the growth of the pathogen. Thus, quantifying adaptation phenomena under growth-limiting environments, such as in fermented dairy and meat products or products preserved in brine, is essential for reliable growth simulations of L monocytogenes during transportation and storage of foods.     

Validation of food-grade salts of organic acids as ingredients to control Listeria monocytogenes on pork scrapple during extended refrigerated storage

This study was conducted to investigate control of Listeria monocytogenes on pork scrapple during storage at 4°C. In phase I, scrapple was formulated, with or without citrate-diacetate (0.64%), by a commercial processor to contain various solutions or blends of the following antimicrobials: (i) lactate-diacetate (3.0 or 4.0%), (ii) lactate-diacetate-propionate (2.0 or 2.5%), and (iii) levulinate (2.0 or 2.5%). Regardless of whether citrate-diacetate was included in the formulation, without the subsequent addition of the targeted antimicrobials pathogen levels increased ca. 6.4 log CFU/g within the 50-day storage period. In the absence of citrate-diacetate but when the targeted antimicrobials were included in the formulation, pathogen numbers increased by ca. 1.3 to 5.2 log CFU/g, whereas when citrate-diacetate was included with these antimicrobials, pathogen numbers increased only by ca. 0.7 to 2.3 log CFU/g. In phase II, in the absence of citrate-diacetate, when the pH of the lactate-diacetate-propionate blend (2.5%) was adjusted to pH 5.0 or 5.5 pathogen numbers remained unchanged (≤0.5 log CFU/g increase) over 50 days, whereas when citrate-diacetate was included with the lactate-diacetate-propionate blend adjusted to pH 5.0 or 5.5, pathogen numbers decreased by 0.3 to 0.8 log CFU/g. In phase III, when lower concentrations of the lactate-diacetate-propionate blend (1.5 or 1.94%) were adjusted to pH 5.5, pathogen numbers increased by ca. 6.0 and 4.7 log CFU/g, respectively, whereas when the mixture was adjusted to pH 5.0, pathogen numbers increased by ≤0.62 log CFU/g. Thus, scrapple formulated with lactate-diacetate-propionate (1.5 and 1.94% at pH 5.0) is an unfavorable environment for outgrowth of L. monocytogenes.     

Effect of nisin and its combination with sodium chloride on the survival of Listeria monocytogenes added to raw buffalo meat mince

Antilisterial activity of nisin (Nisaplin), alone at concentrations of 400 and 800 IU/g and in combination with 2% sodium chloride was incorporated in raw buffalo meat mince. Samples of the raw meat mince were inoculated with 10(3) colony forming units (cfu)/g of L. monocytogenes and stored at 4°C for 16 days and at 37°C for 36 h. Initial estimates of pH, extract release volume, mesophilic and psychrophilic counts were found to be 5.74, 48 ml, 3.5×10(5) and 1.0×10(5) cfu/g of meat, respectively. The growth of L. monocytogenes in the treated groups was significantly (P<0.05) inhibited compared to the control group. The degree of inhibition increased with increasing concentration of nisin and decreasing storage temperature. Addition of 2% sodium chloride in combination with nisin increased the efficacy of nisin at both storage temperatures. The pH in the treated groups remained significantly lower (P<0.01) than in the control groups at both 4 and 37°C.     

Reduction of Listeria monocytogenes in Raw Catfish Fillets by Essential Oils and Phenolic Constituent Carvacrol

The antimicrobial activity of various essential oils and carvacrol was determined on fresh raw catfish fillets against a 4-strain Listeria monocytogenes mixture representing serotypes 1/2b, 3b, 4b, and 4c that were predominantly isolated from catfish processing environments. Thyme oil, oregano oil and carvacrol exhibited concentration and time dependent responses in broth against L. monocytogenes; for example 0.5% concentrations resulted in 4 log CFU/mL reduction within 30 min whereas 0.1% concentrations required more than 24 h for the same level of reduction. Lemon, orange, and tangerine oils, at 0.5% showed listeriostatic effect in which 4 log CFU/mL of the initial L. monocytogenes load was unchanged at 4 °C in 10 d whereas 1% concentrations were listericidal in a time dependent manner. Apart from carvacrol, efficacy of tested essential oils in reducing L. monocytogenes and total microbial load from catfish fillet was very limited. Dipping treatment of catfish fillets in 2% carvacrol solution for 30 min at 4 °C reduced L. monocytogenes to an undetectable level from their initial load of 5 log CFU/g and reduced total microbial load from catfish fillets by approximately 5 log CFU/g. In sensory analysis trained panelist preferred control samples over 2% carvacrol treated samples implying potential limitation in applicability of carvacrol for fillet treatments.     

Antimicrobial effects of corn zein films impregnated with nisin, lauric acid, and EDTA

Bacterial growth during food transport and storage is a problem that may be addressed with packaging materials that release antimicrobials during food contact. In a series of five experiments, EDTA, lauric acid (LA), nisin, and combinations of the three antimicrobial agents were incorporated into a corn zein film and exposed to broth cultures of Listeria monocytogenes and Salmonella Enteritidis for 48 h (sampled at 2, 4, 8, 12, 24, and 48 h). Four experiments used starting cultures of 10(8) CFU/ml in separate experiments tested against each bacterium; the fifth experiment examined the inhibitory effect of selected antimicrobial agents on Salmonella Enteritidis with an initial inoculum of 10(4) CFU/ml. L. monocytogenes cell numbers decreased by greater than 4 logs after 48 h of exposure to films containing LA and nisin alone. No cells were detected for L. monocytogenes (8-log reduction) after 24-h exposure to any film combination that included LA. Of all film agent combinations tested, none had greater than a 1-log reduction of Salmonella Enteritidis when a 10(8)-CFU/ml broth culture was used. When a 10(4) CFU/ml of Salmonella Enteritidis initial inoculum was used, the films with EDTA and LA and EDTA, LA, and nisin were bacteriostatic. However, there was a 5-log increase in cells exposed to control within 24 h. The results demonstrate bacteriocidal and bacteriostatic activity of films containing antimicrobial agents.     

普鲁兰多糖/槐糖脂抑菌保鲜膜的制备

目的:为替代传统不可再生塑料保鲜膜,采用经济环保原料制作性能优良的抑菌保鲜膜,并确定其最佳配方。方法:在最佳成膜条件下,采用单因素实验分析普鲁兰多糖、槐糖脂和甘油浓度对成膜性能的影响,并考察了槐糖脂的抑菌浓度。在此基础上设计正交实验,确定抗菌保鲜膜原料的最佳配比,并验证膜液及保鲜膜的保鲜性能。结果:槐糖脂对金黄色葡萄球菌抑制效果显著(p<0.01),2.4 g/L时达到100%抑制;对大肠杆菌和白色假丝酵母菌菌有不同程度的抑制作用,4.0 g/L时抑菌率分别为28.75%和14.53%。确定了膜液的最佳配方为普鲁兰多糖18 g/L、槐糖脂3.6 g/L、甘油8.75 g/L。该膜液及所成的抗菌保鲜膜对樱桃的保鲜效果与对照组相比效果显著(p<0.01)。结论:将槐糖脂生物表面活性剂作为可抗菌保鲜膜的原料,为绿色抗菌保鲜膜的制备工艺提供新的理论依据。     

Effects of slightly acidic low concentration electrolyzed water on microbiological, physicochemical, and sensory quality of fresh chicken breast meat

Anticmicrobial effect of slightly acidic low concentration electrolyzed water (SlALcEW) and strong acidic electrolyzed water (StAEW) on fresh chicken breast meat was evaluated in this study. Meat samples each of 10 ± 0.2 g in weight and 2.5 × 2.5 cm2 in size were experimentally inoculated with Listeria monocytogenes (ATCC 19115) and Salmonella Typhimurium (ATCC 14028) and subjected to dipping treatment (22 ± 2 °C for 10 min) with SlALcEW and StAEW. Shelf-life study was conducted for inoculated and noninoculated meat samples treated with SlALcEW and StAEW at storage temperatures of 5, 15, and 25 °C. Dipping treatment with electrolyzed water significantly (P < 0.05) reduced the background and inoculated pathogens compared to untreated controls. The reduction of 1.5 to 2.3 log CFU/g was achieved by SlALcEW and StAEW against background flora, L. monocytogenes and Salmonella Typhimurium. There was no significant difference (P > 0.05) between the SlALcEW and StAEW treatments efficacy. Comparing treated samples to untreated controls showed that SlALcEW and StAEW treatments extended the shelf life of chicken meat at different temperatures with marginal changes of sensory quality. Although SlALcEW and StAEW treatments showed similar antimicrobial effects but SlALcEW was more beneficial in practical application for its semineutral pH and low chlorine content. PRACTICAL APPLICATION: Food safety issues have led to development of new sanitizers to eliminate spoilage and pathogenic organisms in food. This study provides the foundation for further application of slightly acidic low concentration electrolyzed water (SlALcEW) as a sanitizing agent in meat industry. SlALcEW can be produced on site on demand and no chemicals are necessary except NaCl solution. It does not leave any residue in food due to low chlorine concentration and it is safe to handle for its semineutral pH.     

Package systems and storage times serve as postlethality controls for Listeria monocytogenes on whole-muscle beef jerky and pork and beef smoked sausage sticks

To validate how packaging and storage reduces Listeria monocytogenes on whole-muscle beef jerky and smoked pork and beef sausage sticks, four packaging systems (heat sealed [HS] without vacuum, heat sealed with oxygen scavenger, nitrogen flushed with oxygen scavenger [NFOS], and vacuum) and four ambient temperature storage times were evaluated. Commercially available whole-muscle beef jerky and smoked pork and beef sausage sticks were inoculated with a five-strain L. monocytogenes cocktail, packaged, and then stored at 25.5 °C until enumerated for L. monocytogenes at 0, 24, 48, and 72 h and 30 days after packaging. The interaction of packaging and storage time affected L. monocytogenes reduction on jerky, but not on sausage sticks. A >2-log CFU/cm(2) reduction was achieved on sausage sticks after 24 h of storage, regardless of package type, while jerky had <2-log reductions for all packaging types. At 48 h, log reductions were similar (P. 0.05) for all types of jerky packaging, ranging from 1.26 to 1.72 log CFU/cm(2); however, at 72 h, mean L. monocytogenes reductions were >2 log CFU/cm(2), except for NFOS (1.22-log CFU/cm(2) reduction). Processors could package beef jerky in HS packages with oxygen scavenger or vacuum in conjunction with a 24-h holding time as an antimicrobial process to ensure a >1-log CFU/cm(2) L. monocytogenes reduction or use a 48-h holding time for HS- or NFOS-packaged beef jerky. A >3-log CFU/cm(2) mean reduction was observed for all beef jerky and sausage stick packaging systems after 30 days of 25.5 °C storage.     

Survival of Listeria monocytogenes during the manufacture and ripening of Turkish white cheese

Listeria monocytogenes was enumerated during the manufacture and ripening of Turkish White cheese with particular reference to a) pasteurized milk, b) cheese milk after inoculation with L. monocytogenes (0 h), c) after curd formation (2 h), d) curd after pressing (6 h), e) curd after pH was reduced (17 h), f) curd after salting (32 h), and g) cheeses during ripening. Cheeses were also examined periodically for total solids, moisture and salt contents, pH values and aerobic plate count. An increase in the number of L. monocytogenes was observed during manufacture. Following salting and throughout the storage period, numbers of L. monocytogenes decreased at a rate depending on the salt concentration, starter activity and storage time. The initial microbial number had a significant (P < 0.01) effect on the survival of L. monocytogenes during the storage period.     

Control of Listeria monocytogenes and Salmonella anatum on the surface of smoked salmon coated with calcium alginate coating containing oyster lysozyme and nisin

ABSTRACT:  This study investigated the antimicrobial effect of oyster lysozyme with or without nisin added to calcium alginate (CaAlg) coated on the surface of smoked salmon against Listeria monocytogenes and Salmonella anatum . L. monocytogenes or S. anatum inoculated smoked salmon samples (1 g) were dipped into CaAlg with either oyster lysozyme (OysL) or hen egg white lysozyme (HEWL), with or without added nisin (N), then stored at 4 °C for 35 d. Our results indicated that the effectiveness of oyster lysozyme or hen egg white lysozyme was enhanced when added to calcium alginate coatings. After 35 d at 4 °C the growth of L. monocytogenes and S. anatum was suppressed in the range of 2.2 to 2.8 log CFU/g with CaAlgNOysL or CaAlgNHEWL coatings compared to the control nontreated samples. There was no significant difference between oyster lysozyme and hen egg white lysozyme treatments against L. monocytogenes or S. anatum inoculated on the surface of salmon. Calcium alginate coatings containing lysozyme with nisin or without could be used to reduce the growth of L. monocytogenes and S. anatum on the surface of ready-to-eat smoked salmon at refrigerated temperatures.