Impact of Mechanical Shear on the Survival of Listeria monocytogenes on Surfaces

Abstract: The impact of mechanical surface shear on microbial viability is rarely a subject for exploration in food processing. The objective of this research was to investigate the impact of mechanical shear on the survival of Listeria monocytogenes on surfaces. Mechanical shear created by slicing a model food was explored to investigate the viability of L. monocytogenes. Cell injury/death was readily demonstrated in fluorescence images by confocal microscopy in which the live and dead cells were fluorescently stained green and red, respectively, with a viability dye kit. Images showed that a large percentage of dead cells appeared after slicing, and they were readily transferred from the slicer blade onto the surfaces of sliced agar, indicating that surface shear may cause the lethal effect on L. monocytogenes. Surface transfer results also showed that viable cell counts on agar slices (in a slicing series) followed a consistently decreasing pattern. The cell counts initially at 5 to 6.5 log CFU/slice (slices 1 to 6), decreased to 3 to 4 log CFU/slice (slices 8 to 30), then to 2 to 3 log CFU/slice (slices 31 to 40), and counts would be expected to further decrease if slicing continued. The overall cell recovery (survival) ratio was about 2% to 3% compared to the initial 8.4 log CFU/blade on a 10 cm² edge area. The impact of shear on microbial viability during slicing may contribute 99% of viable cell count reduction. This study provides clear evidence that surface shear can kill foodborne pathogens and reduce cross-contamination. The lethal effects of surface shear may further enhance food safety.     

Modeling transfer of Escherichia coli O157:H7 and Staphylococcus aureus during slicing of a cooked meat product

Cross contamination is one of the most important contributing factors in foodborne illnesses originating in household environments. The objective of this research was to determine the transfer coefficients between a contaminated domestic slicing machine and a cooked meat product, during slicing. The microorganisms tested were Staphylococcus aureus (Gram positive) and Escherichia coli O157:H7 (Gram negative). The results showed that both microorganisms were able to transfer to all slices examined (20 successively sliced) and at different inoculum levels on the blade (10⁸, 10⁶ and 10⁴ cfu/blade). The results also showed that the number of log cfu transferred per slice, during slicing, decreased logarithmically for both microorganisms at inoculum levels of 8 and 6 log cfu/blade. The type of microorganism significantly influenced transfer coefficients (p < 0.05) and there was an interaction between inoculum level and transfer coefficient for S. aureus (p < 0.05), but not E. coli O157:H7. Finally, to describe bacterial transfer during slicing, two models (log-linear and Weibull) were fitted to concentration on slice data for both microorganisms (at 6 and 8 log cfu/blade), obtaining a good fit to data (R²  0.73).     

Modelling transfer of Listeria monocytogenes during slicing of 'gravad' salmon

Transfer of a rifampicin-resistant mutant of Listeria monocytogenes from an inoculated slicing blade to slices of 'gravad' salmon (Salmo salar), and from inoculated salmon fillet to the slicing machine and subsequently to slices of uninoculated fillet was studied. The effect of slicing temperature (0 degrees C, 10 degrees C and room temperature), inoculum level (approx. 3, 5 and 8 log CFU/blade), and attachment time of inoculum to blade (10 min and 2.5 h) were investigated and predictive models of the transfer were produced. In the tests of transfer from inoculated blade (5.9-9.0 log CFU/blade) initially 2.5-5.3 log CFU/g was present on the slices, slowly decreasing to an overall average decrease of 1.6+/-0.2 log CFU/g during slicing of 39 slices; the lowest reduction being 1.3 log CFU/g at 0 degrees C. In tests of transfer from contaminated salmon (7.6+/-0.1 log CFU/fillet) to uninoculated blade and further to uninoculated salmon, the reduction in number of L. monocytogenes in slices was 1.5 log CFU/g during slicing of 39 slices. For example 5.3+/-0.3 log CFU/g was transferred to second slice when the inoculum level was 8.4+/-0.4 log CFU/blade, but clearly (p<0.05) lower total number of L. monocytogenes were transferred to slices when the inoculum level was lower, the temperature was colder or the attachment time was longer. There was a progressive exponential reduction in the quantity of L. monocytogenes transferred and, based on statistical parameters, an exponential model (y=ae((-x/b))) fit the data from different test conditions and was suitable for predicting an expected number of L. monocytogenes on the salmon slices. Based on the predicted values, the logarithmic reduction in number of L. monocytogenes in slices was highest at room temperature with an inoculum level of 8.4+/-0.4 log CFU/blade (attachment time 10 min); the other test conditions differed significantly from this (p<0.05). Despite statistically significant differences, in all test conditions the number of bacteria were predicted to reduce quite rapidly (i.e. after slicing of the fourth fillet) to <1 log CFU/g, though this prediction was an extrapolation after 39 slices. The predictive models described herein can assist salmon processors and regulatory agencies in assessing cross-contamination from contaminated slicing machines to product and in designing risk management strategies.     

Modeling Surface Transfer of Listeria monocytogenes on Salami during Slicing

ABSTRACT: Listeria monocytogenes has been implicated in several listeriosis outbreaks linked to the consumption of presliced ready‐to‐eat (RTE) deli meats, which has drawn considerable attention in regard to possible cross‐contamination during slicing operation at retail and food service environments. Salami with 15% fat (a moderate fat content deli item) was used to investigate the transfer of L. monocytogenes between a meat slicer and salami slices and to understand its impact on food safety. A 6‐strain cocktail of L. monocytogenes was inoculated onto a slicer blade to an initial level of approximately 3, 5, 6, 7, or 9 log CFU/blade (or approximately 2, 4, 5, 6, or 8 log CFU/cm² of the blade edge area), and then the salami was sliced to a thickness of 1 to 2 mm (case I). For another cross‐contamination scenario, a clean blade was first used to slice salami loaf that was previously surface‐inoculated with L. monocytogenes (approximately 3, 5, 6, 7, 8, or 9 log CFU/100 cm² area), followed by slicing the uninoculated salami loaf (case II). The salami slicing rate was maintained at an average of 3 to 4 slices per minute in all the tests. The results showed that the empirical models developed in this study were reasonably accurate in describing the transfer trend/pattern of L. monocytogenes between the blade and salami slices if the inoculum level was > 5 log CFU on the salami or blade. With an initial inoculum at 3 or 4 log CFU, the experimental data seemed to suggest a rather random pattern of bacterial transfer between blade and salami. The currently developed models are microbial load (n), sequential slice index (X), and contamination route dependent, which might limit their applications to certain conditions. However, the models may be further applied to predict the 3 or 4 log CFU level (and below) cross‐contamination of salami slicing process. Considering only few data are available in the literature regarding food pathogen surface transfer, the empirical models may provide a useful tool in building risk assessment procedures.     

Slicing frozen meat with an oscillating knife

The forces, and hence fracture energies, required to cut frozen meat are presented in this paper and the merits of applying vibrations to a cutting blade are considered. A knife oscillating in a slicing action was used to cut horse M. semimembranosus and loin muscle M. longissimus dorsi over a range of temperatures (-1.5°C to -30°C) and vibration frequencies (0-1000 Hz). The blade required less force to cut when slicing than when not slicing; the decrease in force was proportional to the velocity of the slicing motion. If the average relative slicing velocity of the blade with respect to the meat was greater than 164 mm/s then the cutting force reduced significantly. The reduction was due to a lower requirement for energy to produce the new material surface (up to 80% reduction) and also a reduction in the plastic energy required to deform the off-cut by the blade (up to 30% reduction). The surface energy was reduced because the fracture mechanism was altered by the slicing action. The plastic energy was reduced because the slicing blade fractured the meat fibres with less strain (and hence less material deformation around the process zone) than a blade pressed directly into the meat. Vibration frequencies of 10-100 Hz were required to generate the required slicing motion with the equipment available. A vibrating cutting blade could have a combination of chopping and slicing motions superimposed upon it. These would reduce both the friction between the knife blade and the meat, as well as the surface and plastic energy required to cut the meat.     

Ascorbic Acid Retention in Shredded Iceberg Lettuce as Affected by Minimal Processing

The effects of slicing method, packaging atmosphere and storage temperature were determined on total ascorbic acid (TAA) content of modified atmosphere packaged shredded lettuce. TAA was extracted from the lettuce samples and levels were monitored using either titration with 2,6-dichlorophenolindophenol solution or an assay kit. Slicing affected (p<0.05) ascorbic acid retention in the order manual tearing > manual slicing > machine slicing. Flushing with 100% nitrogen increased retention (～5%, p<0.05) over packages with product modified atmospheres. Storage at 3°C increased retention (～20%, p<0.05) compared with storage at 8°C. Scores for product appearance generally followed losses of TAA in the lettuce (p<0.05).     

Mathematical modeling the cross-contamination of Escherichia coli O157:H7 on the surface of ready-to-eat meat product while slicing

Microbial cross-contamination either at home or production site is one of the major factors of causing contamination of foods and leading to the foodborne illness. The knowledge regarding Escherichia coli O157:H7 surface transfer on ready-to-eat (RTE) deli meat and the slicer used for slicing different RTE products are needed to ensure RTE food safety. The objectives of this study were to investigate and to model the surface cross-contamination of E. coli O157:H7 during slicing operation. A five-strain cocktail of E. coli O157:H7 was inoculated directly onto a slicer's round blade rim area at an initial level of ca. 4, 5, 6, 7 or 8 log CFU/blade (ca. 3, 4, 5, 6 or 7 log CFU/cm² of the blade edge area), and then the RTE deli meat (ham) was sliced to a thickness of 1–2 mm. For another cross-contamination scenario, a clean blade was initially used to slice ham which was pre-surface-inoculated with E. coli O157:H7 (ca. 4, 5, 6, 7 or 8 log CFU/100 cm² area), then, followed by slicing un-inoculated ham. Results showed that the developed empirical models were reasonably accurate in describing the transfer trend/pattern of E. coli O157:H7 between the blade and ham slices when the total inoculum level was ≥5 log CFU on the ham or blade. With an initial inoculum level at ≤4 log CFU, the experimental data showed a rather random microbial surface transfer pattern. The models, i.e., a power equation for direct-blade-surface-inoculation, and an exponential equation for ham-surface-inoculation are microbial load and sequential slice index dependent. The surface cross-contamination prediction of E. coli O157:H7 for sliced deli meat (ham) using the developed models were demonstrated. The empirical models may provide a useful tool in developing the RTE meat risk assessment.     

Transfer of Listeria monocytogenes during slicing of turkey breast, bologna, and salami with simulated kitchen knives

In response to continued concerns regarding Listeria cross-contamination during the slicing of deli meats, a series of specially prepared grade 304 and 316 stainless steel kitchen knife blades was inoculated with a six-strain Listeria monocytogenes cocktail (10(8), 10(5), and 10(3) CFU per blade) composed of two weak, two medium, and two strong biofilm-forming strains. The blades were then attached to an Instron 5565 electromechanical compression analyzer and used to slice whole chubs of delicatessen turkey breast, bologna, and salami to entirety (30 slices) at a cutting speed of 8.3 mm/s. Homogenates of the slices in University of Vermont Medium were surface or pour plated with modified Oxford agar and then enriched. Listeria transfer from knife blades inoculated at 10(8) CFU per blade was logarithmic, with a 2-log decrease seen after 8 to 12 slices and direct counts obtained thereafter out to 30 slices. However, blades containing 10(5) and 10(3) CFU per blade typically yielded direct counts out to only 20 and 5 slices, respectively. Normalizing data on a log scale for the first 10 slices resulted in significantly greater Listeria transfer and "tailing" from grade 304 as opposed to grade 316 stainless (P < 0.05) for all three products. After 1 year of use, surface roughness values as determined by surface profilometry were significantly greater (P < 0.001) for grade 304 than for grade 316 stainless blades. Cutting force and blade sharpness were not significantly different (P > 0.05) within stainless steel grade (P < 0.05) for each product. However, significant differences in cutting force were seen between salami and turkey (P < 0.05) for grades 304 and 316 stainless, respectively. In addition to compositional differences in the deli meats and knife blades, wear and scoring on the blade likely affected Listeria transfer during slicing.     

莲藕切片装置的设计

对莲藕切片装置的结构、工作原理作了介绍,对关键零部件进行了结构设计,为制造莲藕切片装置提供了理论上的设计依据。     

新型鲜桃切分去核机设计与分析

[目的]解决鲜桃切片去核生产自动化的技术难题。[方法]设计新型鲜桃切分去核机,利用数学分析法对切片去核刀具进行简化和运动分析,得出该机构的运动特性方程和曲线图;利用SolidWorks Motion软件对切片去核刀具机构进行运动仿真分析,得出该机构的运动特性曲线图,验证数学分析的正确性,同时也验证切片去核刀具设计的合理性。[结果]该机利用PLC控制,包括鲜桃输送链上料、鲜桃定位、切片刀具运动等,通过现场试验结果分析,鲜桃切片去核机平均切分率达到99.39%,平均去核率达到99.15%,平均破坏率低于0.12%。[结论]该新型鲜桃切分去核机能够实现鲜桃的自动定位、切分、去核等。     

Microbiological quality of fresh-cut sweet potatoes

Sweet potato roots were dipped in various concentrations of chlorine for 5 min at 1 or 20 °C before and after slicing, and then stored at 2 or 8 °C for 14 days to evaluate the effects of different chlorine treatments and storage temperatures on the microbiological quality of fresh‐cut sweet potato slices. The microflora of fresh‐cut sweet potato slices was dominated by mesophiles, followed by psychrotrophs and fungi initially and during storage. The 2 °C storage was necessary to keep the microbial load at a low level. No spoilage was observed in fresh‐cut sweet potatoes at both storage temperatures for 14 days. Chlorination of sweet potatoes before slicing was not effective in ensuring acceptable microbiological quality of fresh‐cut sweet potatoes. Dipping slices in 200 ppm chlorine at 1 °C reduced the population of all micro‐organisms during storage.     

单晶硅棒切方专用金刚石外圆切割片技术要求及制造工艺探讨

文章对单晶硅棒切方专用金刚石外圆切割片的技术要求及制造工艺进行了探讨。在金刚石外圆切割片制造工艺中,采用双层电沉积法制造金刚石外圆切割片,对基体材料、刃口厚度、偏摆度、工艺规范及金刚石的选用处理都有严格的要求：选用高性能工具钢为基体材料,进行尺寸、偏摆度及应力控制;合理的工艺规范使制造出的切割片具有足够高的韧性和抗冲击能力,使金刚石发挥出最佳的磨削效果;选用适宜金刚石,并对金刚石粒度及表面进行处理,使金刚石出刃均匀,且与电沉积层紧密结合,提高使用寿命。     

Effectiveness of Hydrothermal‐Calcium Chloride Treatment and Chitosan on Quality Retention and Microbial Growth during Storage of Fresh‐Cut Papaya

Rapid degradation of fresh‐cut papaya limits its marketability. Hydrothermal treatments in combination with a calcium dip, applied to whole fruit before slicing, and also the application of chitosan as a coating film, have been found to have very good results in maintaining the quality of fresh‐cut fruits. Based on these considerations, the aim of this study was to evaluate the effect of hydrothermal treatment (HT; 49 °C, 25 min) containing calcium chloride (Ca; 1%, w/v) followed by dipping in chitosan (Chit; 1%, w/v, 3 min) on the physical, chemical, and microbial qualities of papaya slices stored at 5 °C for 10 d. Pulp color, firmness, ascorbic acid, total phenolics, β‐carotene, and lycopene were evaluated every 2 d while the microbial quality (mesophilics, psychrophilics, molds, and yeasts) was evaluated every 5 d. Fruit treated with HT‐Ca and HT‐Ca + Chit showed better color and firmness retention than Control and Chit. Papaya slices treated with HT‐Ca + Chit had higher nutritional content and lower microbial growth at the end of storage. The application of the HT‐Ca + Chit could be used to reduce deterioration processes, maintaining physical, chemical, and microbial qualities and increasing the shelf life of fresh‐cut papaya stored at 5 °C.     

一种猕猴桃削皮和切片设备的研制

为解决猕猴桃果脯加工中削皮和切片的问题,研发了猕猴桃削皮切片一体机,该机采用多工位转盘式结构,分为削皮和切片两个功能区,将多自由度手臂应用到猕猴桃削皮中。对该机的技术方案、工作转盘的设计、多自由度手臂的应用、试验情况等进行了论述。     

涂布机刮刀改造节能技术的研究与应用

将涂布机刮刀由气刀改造为刮刀,节约了水、电、煤等各项能源消耗,提高了机器运行效率;节约涂料,改善工作环境;改善了纸张外观性能,提高了纸面的平滑度、光泽度等技术指标,提升了产品档次。     

High voltage atmospheric cold plasma technology as a food safety intervention for decontamination of cutting tools during ready-to-eat poultry meat slicing

This study aimed to build a prototype that integrates a cold plasma capability into a manual meat slicer while it is in operation to minimize cross-contamination from the circular cutting blade. A high voltage atmospheric cold plasma (HVACP) generator was attached to a meat slicer with a rotating 22.5-cm diameter stainless steel slicing blade. The meat slicer with the installed cold plasma generator was contained within a sealed, clear acrylic box. Listeria innocua (LI) was selected as the test organism, and initial testing was performed on stainless-steel coupons in room air at a relative humidity ranging from 30 to 90% for treatment times up to 240 s. Results found that 240 s and 90% RH showed a 3.0-log reduction of LI. These conditions were then replicated using “dirty” stainless-steel knife while rotating. The results showed only a 0.5-log LI reduction. The gas was changed from air to MA65 gas blend (65% O₂, 30% CO₂ and 5% N₂) and then a 1.91 log LI reduction was achieved on the “dirty” knife.Industrial relevanceDue to the rapid processing speeds required in the food industry, it is difficult to assure the complete cleanliness of the tools and surfaces used at all times, and then, operations like the cutting /slicing step are still one of the critical points for cross-contamination during meat processing. High voltage atmospheric cold plasma (HVACP) is a practical intervention that has the potential to deliver a continuous, in-situ decontamination of the knife during operation to mitigate the risk of cross-contamination. The developed prototype, as shown in this study, can deliver beneficial results in short treatment time and with minimal inputs of air and electricity, without heating effects, minimizing the use of water, or the use of sanitizers.     

造纸机刮刀装置的设计原则及其优化设计

基于造纸机刮刀装置运行的原理和功能、装置分类和设计等方面分析造纸机刮刀装置设计的原则和优化内容,以此为刮刀装置设计提出原则和构想。     

特大系列皮革削匀机刀片的研制

通过与国外刀片CK101的组成对比和加工工艺的改进,研制用国产T10A钢制造削匀机刀片的过程,展示了良好的市场前景。     

刮刀涂布在生产中的应用及常见纸病分析

介绍了刮刀涂布的工作原理及其在生产中的应用,重点讨论了刮刀涂布中常见纸病及处理措施,并比较了硬刮刀和软刮刀的优缺点及应用注意事项。