Survival and growth of Listeria species in a model ready-to-use vegetable product containing raw and cooked ingredients as affected by storage temperature and acidification

Summary The survival and growth of Listeria monocytogenes and L. innocua strains inoculated onto cooked sweet corn and fresh bean sprouts packed individually, and as components of a combination product, were examined at refrigeration and mild abuse temperatures. Growth rates were both temperature and vegetable dependent. Maximal growth rates (1.14 ± 0.1log CFU/day) were identified on cooked sweet corn at 12 °C. The inclusion of cooked sweet corn did not significantly increase ( P > 0.05) the growth rate or final Listeria population density of bean sprouts stored at 8 °C and 12 °C. The sensory quality of bean sprouts was relatively temperature independent for the initial 48 h of storage, but was maximized (4 days shelf life) at 3 °C. Acidification of sweet corn to pH 5, particularly with citric acid, slowed Listeria growth and could be an additional hurdle to supplement temperature in maintaining the safety of minimally processed vegetable combination products.     

Utilization of Zein Coating and Sorbic Acid to Reduce Listeria monocytogenes Growth on Cooked Sweet Corn

Several proteins, lipids and waxes were tested as edible coatings on sweet corn. Only zein, a natural constituent of corn, gave a continuous adhesive and stable coating with satisfactory sensory properties. After 8 days at 10 °C, the population of L. monocytogenes was 10‐fold lower on coated sweet corn than on non‐coated sweet corn indicating a barrier effect of zein coating. Sorbic acid was incorporated in the coating at a concentration required to inhibit L. monocytogenes growth (approximately 1 mg sorbic acid/g of sweet corn). The inhibitory concentration was the same for both coated and non‐coated sweet corn. Zein coating therefore did not improve the preservative effect of sorbic acid.     

Nisin和柠檬酸对鲜切皇冠梨储藏期间单增李斯特菌生长的影响

分别采用0.05mg/m L乳酸链球菌素(Nisin)、0.3%柠檬酸复配溶液和自来水清洗接种单增李斯特菌(LM)的鲜切皇冠梨,将清洗后的鲜切皇冠梨分别于4、12、24℃的条件下储藏,以未清洗的样品为对照,测定储藏过程中LM的生长情况。结果显示Nisin和柠檬酸清洗能显著降低(p<0.05)鲜切皇冠梨中LM的初始带菌量。在4℃储藏过程中,Nisin和柠檬酸清洗的鲜切皇冠梨中LM数量没有明显变化(p>0.05),自来水清洗和未清洗的鲜切样品中LM数量略有升高。在12℃和24℃储藏期间,三种处理方式的鲜切皇冠梨LM数量均显著上升(p<0.05)。Nisin和柠檬酸复配清洗处理结合低温储藏能有效控制鲜切皇冠梨中LM的生长。      

利用玉米粉产柠檬酸黑曲霉的筛选

以从土壤中分离的黑曲霉为出发菌种,经过紫外线和DES的诱变处理,得到了一株能利用玉米粉为原料的黑曲霉菌株AS35.经过摇瓶发酵柠檬酸的对照试验,结果表明:该菌株能够较好地利用玉米粉,产酸能力达8.6%,原料转化率达66.2%,较原始菌种大大提高.     

Application of the Weibull model to describe inactivation of Listeria monocytogenes and Escherichia coli by citric and lactic acid at different temperatures

Inactivation of Listeria monocytogenes and Escherichia coli by citric (10‐150 g L^?1) and lactic (1‐60 mL L^?1) acids at different temperatures (4, 20, 40 °C) has been investigated. Bactericidal effect of both acids was dependent on time and temperature of exposure and acid concentration. Survival curves of L. monocytogenes treated by lactic acid were concave downward and those treated by citric acid were linear. On the other hand, survival curves of E. coli treated by both organic acids were concave upward. Shape of survival curves depended on the type of acid but not on the treatment temperature. A mathematical model based on the Weibull distribution accurately described the kinetics of inactivation of both microorganisms by both acids. This model allowed quantification and comparison of the acid resistance of L. monocytogenes and E. coli. Lactic acid was more effective than citric acid and E. coli was more sensitive to both acids than L. monocytogenes. Copyright © 2006 Society of Chemical Industry     

Antimicrobial activity of lauric arginate-coated polylactic acid films against Listeria monocytogenes and Salmonella typhimurium on cooked sliced ham

A novel type of environmentally friendly packaging with antibacterial activity was developed from lauric arginate (LAE)-coating of polylactic acid (PLA) films after surface activation using a corona discharge. Scanning electron microscopy (SEM)-based analysis of the LAE/PLA films confirmed the successful coating of LAE on the PLA surface. The mechanical properties of the LAE/PLA films with different levels of LAE-coating (0% to 2.6%[w/w]) were essentially the same as those of the neat PLA film. The antibacterial activity of the LAE/PLA films against Listeria monocytogenes and Salmonella enterica Serovar Typhimurium (S. Typhimurium) was confirmed by a qualitative modified agar diffusion assay and quantitative JIS Z 2801:2000 method. Using the LAE/PLA film as a food-contact antimicrobial packaging for cooked cured ham, as a model system, suggested a potential application to inhibit L. monocytogenes and S. Typhimurium on ham with a 0.07% (w/w) LAE coating on the PLA when high transparency is required, as evidenced from the 2 to 3 log CFU/tested film lower pathogen growth after 7 d storage but even greater antibacterial activity is obtained with a LAE coating level of 2.6% (w/w) but at the cost of a reduced transparency of the finished product. This article shows how we can simply develop functional green packaging of PLA for food with effective and efficient antimicrobial activity by use of LAE coating on the surface via corona discharge. PRACTICAL APPLICATION: The effectiveness of an innovative antimicrobial LAE-coated PLA film against foodborne pathogens was demonstrated. Importantly, the application of the LAE to form the LAE-coated PLA film can be customized within current film manufacturing lines.     

Combined use of bacteriocin‐producing strains to control Listeria monocytogenes regrowth in raw pork meat

Avoiding the presence of Listeria in meat and dairy products is a major challenge for the food industry. In this work, a Lactobacillus curvatus strain producing the bacteriocin sakacin P and a Pediococcus acidilactici strain producing another bacteriocin, pediocin AcH, were used as starter cultures under laboratory conditions in a Listeria‐seeded raw‐pork‐meat matrix, which was then stored for 6 weeks at 4 °C. At 1 week intervals during the storage period, the antilisterial activity was evaluated. When either strain was added alone, the Listeria monocytogenes cfu count initially dropped from 10² cfu g^?1 to an undetectable level by the end of week 1 or 2, but this was followed by a rebound (regrowth) 1 week later. When both strains were added together to the meat matrix, rebound was delayed, Listeria remaining undetected from the end of week 1 to the end of week 5. A rebound was observed 6 weeks post‐inoculation, but fewer than 10 cfu g^?1 were counted. The use of more than one bacteriocin‐producing strain may thus overcome some of the problems limiting the effectiveness of bacteriocins in food systems.     

The effect of using citric or acetic acid on survival of Listeria monocytogenes during fish protein recovery by isoelectric solubilization and precipitation process

Isoelectric solubilization and precipitation (ISP) is a protein recovery process effective at reducing Listeria innocua, a nonpathogenic bacterium typically used as a surrogate for L. monocytogenes in recovered trout protein. The response of L. monocytogenes to ISP processing was determined and compared to the response of L. innocua. Headed and gutted rainbow trout were inoculated with L. monocytogenes (10.16 log CFU/g), homogenized, and pH-adjusted with granular citric acid (pH 2.0 and 2.5) or glacial acetic acid (pH 3.0 and 3.5). Proteins were solubilized and centrifugation was used to remove insoluble components (skin, insoluble protein, so on). The supernatant was returned to the protein isoelectric point (pH 5.5) with NaOH and centrifuged to remove precipitated protein. Microbial load was enumerated on both growth and selective media; recovery was not significantly different (P > 0.05). Surviving cells from each component (protein, insoluble, and water) were compared to initial inoculum numbers. Significant reductions were detected at all pH (P < 0.05). The greatest reductions were at pH 3.0 with acetic acid, with a mean log reduction of 3.03 in the combined components, and a 3.53 log reduction in the protein portion. Data were compared to results from a previous study using L. innocua. Significant differences (P < 0.05) in recovery were found between the 2 species at pH 2.0 and 3.0 with greater recovery of L. monocytogenes, regardless of processing pH or acid type. These results demonstrate the variability in resistance between species and indicate that L. innocua is not an appropriate surrogate for L. monocytogenes for ISP processing with organic acids.     

2010~2016年云南省熟肉制品和餐饮食品中单增李斯特菌污染情况调查分析

目的 了解2010～2016年云南省市售熟肉制品和餐饮食品中单增李斯特菌污染情况调查分析。方法 在全省16个州市县中选取超市、农贸市场、零售及餐饮环节等为采样点, 随机采取熟肉制品1465份和餐饮食品3674份, 按照GB 4789.30-2010《食品安全国家标准 食品微生物学检验 单核细胞增生李斯特氏菌检验》及《全国食源性致病菌监测工作手册》进行检测和鉴定。结果 1465份熟肉制品中单增李斯特菌检出率为2.18%(32/1465), 3674份餐饮食品中单增李斯特菌阳性率为1.44%(53/3674)。在不同流通环节中, 熟肉制品和餐饮制品中检出率最高的分别为便利店和超市, 分别为9.09%(5/55)和1.67%(3/180)。在不同的监测地区, 熟肉制品和餐饮制品检出率最高均为昭通地区, 分别为7.8%(11/141)和7.17%(18/251)。结论 单增李斯特菌在熟肉制品及餐饮食品中均有检出, 说明云南省的食品中存在一定的单增李斯特菌污染, 对消费者的安全有潜在风险, 相关监管部门应持续加强监管, 预防食源性疾病的发生。     

肽核酸荧光原位杂交技术快速检测食品中的李斯特菌属及单增李斯特菌

目的建立利用肽核酸荧光原位杂交技术(PNA-FISH)快速检测食品中李斯特菌属及单增李斯特菌的方法。方法针对李斯特菌属、单增李斯特菌分别设计合成2份PNA探针lis-16S-1、lm-16S-2,并建立荧光原位杂交技术,优化杂交条件,对选取的13株李斯特菌和其他9株非李斯特菌进行检测,验证探针的特异性和灵敏度,并对118份食品样品用LB肉汤2次增菌培养后进行PNA-FISH检测。结果探针灵敏度和特异性均为100%,从118份食品中检出14株李斯特菌和8株单增李斯特菌,结果与API方法和VITEK方法鉴定结果一致。结论 PNA-FISH方法可靠易行,对从食品中检测致病性单增李斯特菌有较高的实用性。     

Rapid detection of Listeria monocytogenes in raw milk with loop-mediated isothermal amplification and chemosensor

Loop-mediated isothermal amplification (LAMP) allows a rapid amplification of nucleic acids under isothermal conditions. It can be combined with a rhodamine-based dual chemosensor for much more efficient, field-friendly detection of Listeria monocytogenes. In this report, LAMP was performed at 63 °C for 10 min, followed by a rapid reaction of DNA amplification and the byproduct, pyrophosphate ion, with a rhodamine-based dual chemosensor and Cu(2+) is visualized as a disappearance of red color. The detection limit of L. monocytogenes by the LAMP-chemosensor was 8 to 10 cells per reaction tube, and the total assay time including 10 min for rapid DNA extraction was approximately 30 min. Data on naturally contaminated raw milk samples indicated that the LAMP method was highly specific and sensitive, giving 100% concordance with the ISO 10560 reference method. The results showed that the LAMP-chemosensor method has the advantages of better sensitivity and speed and less dependence on equipment than the standard Polymerase Chain Reaction for specifically detecting low levels of L. monocytogenes DNA, and this can be useful in the field as a routine diagnostic tool. PRACTICAL APPLICATION: The LAMP-chemosensor method reported here provided a powerful tool for detection of L. monocytogenes in raw milk samples due to its specificity, sensitivity, and rapidity.     

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.     

Effects of Organic Acid Salt Solutions on Sensory and Other Quality Characteristics of Frankfurters

ABSTRACT: The technical feasibility of using organic acid salts for surface treatment of frankfurters to determine their sensory and other quality characteristics and their ability to inhibit bacterial growth was investigated. To be practically effective, such treatments for frankfurters should have no adverse effects on meat quality attributes, including sensory quality, color, or texture. A 6% sodium diacetate + potassium benzoate (SD/PB) treatment significantly increased meat flavor, and a 3% sodium lactate + sodium diacetate + potassium benzoate (SL/SD/PB) treatment significantly decreased smoke flavor compared with the control group, but there was no significant difference between controls and the surface-treated frankfurters when comparing salty, sour, or pepper flavors. On the other hand, the SL/SD/PB at either 3% or 6% significantly increased the lightness ( L *) and decreased the redness ( a *) value for frankfurters compared with the control group. For storage time longer than 2 mo, the L * value significantly increased and the a * value decreased. Evaluation of quality characteristics showed that after surface treatment with organic acid salts, no differences were observed between controls and treated frankfurters for pH, nitrite concentration, or sodium content.     

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

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

The effect of phytic acid on oxidative stability of raw and cooked meat

The effects of phytic acid addition (0.1, 1 and 5 mM) to pork and beef homogenates on TBARS and metmyoglobin levels in raw meat, and TBARS and heme iron contents in cooked meat during 3 days of storage at 4 °C were investigated. Also, the role of inositol as a potential synergist of IP₆ (phytic acid) was examined. IP₆ effectively decreased the TBARS accumulation in raw and cooked meat homogenates. The metmyoglobin formation was inhibited in raw beef by phytic acid in a dose-dependent manner. The effect of IP₆ was more pronounced in cooked meat than in raw and in cooked beef homogenates more than pork. Inositol did not enhance antioxidant action of phytic acid in minced meat.     

沙门氏菌和单增李斯特菌诱导性耐酸响应机制的研究进展

沙门氏菌和单增李斯特菌被认为是肉制品中最重要的食源性致病菌。它们在弱酸环境下会发生强烈的诱导性耐酸响应,同时诱导产生高毒、耐酸、耐渗透压的高危菌株,是影响消费者健康安全的重大隐患。本文主要从沙门氏菌和单增李斯特菌产生诱导耐酸的发现过程、诱导耐酸响应的危害、产生诱导耐酸的影响因素方面进行概述,进一步从pH值稳态系统、应激蛋白分子的调控及细胞膜组成和流动性调控的角度分析了产生诱导耐酸响应的分子机制。