A Predictive Model for Heat Inactivation of Listeria monocytogenes Biofilm on Stainless Steel

2004 ◽  
Vol 67 (12) ◽  
pp. 2712-2718 ◽  
Author(s):  
R. A. N. CHMIELEWSKI ◽  
JOSEPH F. FRANK
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Listeria Monocytogenes ◽  
Predictive Model ◽  
Enrichment Culture ◽  
Hot Water ◽  
Management Tool ◽  
Heat Inactivation ◽  
Heat Treated ◽  
Processing Plants

Heat treatment of potential biofilm-forming sites is sometimes used for control of Listeria monocytogenes in food processing plants. However, little information is available on the heat treatment required to kill L. monocytogenes present in biofilms. The purpose of this study was to develop a predictive model for the heat inactivation of L. monocytogenes in monoculture biofilms (strains Scott A and 3990) and in biofilms with competing bacteria (Pseudomonas sp. and Pantoea agglomerans) formed on stainless steel in the presence of food-derived soil. Biofilms were produced on stainless steel coupons with diluted tryptic soy broth incubated for 48 h at 25°C. Duplicate biofilm samples were heat treated for 1, 3, 5, and 15 min at 70, 72, 75, 77, and 80°C and tested for survivors using enrichment culture. The experiment was repeated six times. A predictive model was developed using logistic regression analysis of the fraction negative data. Plots showing the probability of L. monocytogenes inactivation in biofilms after heat treatment were generated from the predictive equation. The predictive model revealed that hot water sanitation of stainless steel can be effective for inactivating L. monocytogenes in a biofilm on stainless steel if time and temperature are controlled. For example, to obtain a 75% probability of total inactivation of L. monocytogenes 3990 biofilm, a heat treatment of 80°C for 11.7 min is required. The model provides processors with a risk management tool that provides predicted probabilities of L. monocytogenes inactivation and allows a choice of three heat resistance assumptions. The predictive model was validated using a five-strain cocktail of L. monocytogenes in the presence of food soil.

scholarly journals Persistent and Nonpersistent Listeria monocytogenes Contamination in Meat and Poultry Processing Plants

2003 ◽  
Vol 66 (11) ◽  
pp. 2062-2069 ◽  
Author(s):  
JANNE M. LUNDÉN ◽  
TIINA J. AUTIO ◽  
A.-M. SJÖBERG ◽  
HANNU J. KORKEALA
Keyword(s):  
Heat Treatment ◽  
Listeria Monocytogenes ◽  
Sampling Site ◽  
Pfge Type ◽  
Processing Plant ◽  
Post Heat Treatment ◽  
Common Location ◽  
Heat Treated ◽  
Processing Plants ◽  
Poultry Processing

Contamination analysis of persistent and nonpersistent Listeria monocytogenes strains in three meat processing plants and one poultry processing plant were performed in order to identify factors predisposing to or sustaining persistent plant contamination. A total of 596 L. monocytogenes isolates were divided into 47 pulsed-field gel electrophoresis (PFGE) types by combining the restriction enzyme patterns of AscI (42 patterns) and ApaI (38 patterns). Persistent and nonpersistent strains were found in all plants. Nonpersistent PFGE types were found mostly at one sampling site, with the processing environment being the most common location, whereas the persistent strains were found at several sampling sites in most cases. The processing machines were frequently contaminated with persistent L. monocytogenes PFGE types, and it was of concern that surfaces having direct contact with the products were contaminated. The role of the processing machines in sustaining contamination and in contaminating the products appeared to be important because the final product of several processing lines was contaminated with the same L. monocytogenes PFGE type as that found in the processing machine. The proportion of persistent PFGE types in heat-treated products was eight times higher than in the raw products, showing the importance of the persistent PFGE types as contaminants of the final heat-treated products. The contamination status of the processing lines and machines appeared to be influenced by the compartmentalization of the processing line, with poor compartmentalization increasing L. monocytogenes contamination. The separation of raw and post–heat treatment areas seemed especially important in the contamination status of post–heat treatment lines.

Behavior of Listeria monocytogenes in a Pseudomonas putida Biofilm on a Condensate-Forming Surface

2004 ◽  
Vol 67 (2) ◽  
pp. 322-327 ◽  
Author(s):  
ASHRAF N. HASSAN ◽  
DAWN M. BIRT ◽  
JOSEPH F. FRANK
Keyword(s):  
Stainless Steel ◽  
Listeria Monocytogenes ◽  
Pseudomonas Putida ◽  
Microscopic Observation ◽  
Pure Culture ◽  
Extracellular Polymeric Substances ◽  
Plate Count ◽  
Free Surfaces ◽  
Processing Plants ◽  
Humidity Chamber

Listeria monocytogenes has been isolated from condensate-forming surfaces in food processing plants. The objective of this research was to observe the behavior of L. monocytogenes on condensate-covered stainless steel with a Pseudomonas putida biofilm. L. monocytogenes–containing biofilms, either with or without added chicken protein, were incubated in a high humidity chamber at 12°C to allow formation of condensate. Samples were analyzed for attached and unattached L. monocytogenes and total plate count periodically for 35 days. Samples were also taken for microscopic observation of Listeria and bacterial extracellular polymeric substances (EPS). L. monocytogenes attached in significantly greater numbers (>3-log difference) to surfaces with preexisting P. putida biofilms than to Pseudomonas-free surfaces. L. monocytogenes survived in the presence or absence of P. putida with no added nutrients for 35 days, with numbers of survivors in the range of 3 to 4 log CFU/cm2 in the presence of P. putida and less than 2.9 log CFU/cm2 in pure culture. Attached and unattached L. monocytogenes were at similar levels throughout the incubation under all conditions studied. The addition of protein to the biofilms allowed growth of L. monocytogenes in pure culture during the first 7 days of incubation. Numbers of L. monocytogenes were not affected by the presence of P. putida when protein was present. Unattached L. monocytogenes were at levels of 3.6 to 6.7 log CFU/cm2 on the protein-containing surfaces. Microscopic observation of the condensate-covered biofilms indicated that L. monocytogenes formed microcolonies embedded within an EPS matrix over a 28-day period. This research demonstrates that L. monocytogenes can survive on condensate-forming stainless steel in low and high nutrient conditions, with or without the presence of Pseudomonas biofilm. The Listeria can detach and, therefore, have the potential to contaminate product.

Control of Listeria monocytogenes with Combined Antimicrobials after Postprocess Contamination and Extended Storage of Frankfurters at 4° C in Vacuum Packages

2002 ◽  
Vol 65 (2) ◽  
pp. 299-307 ◽  
Author(s):  
JOHN SAMELIS ◽  
GERARD K. BEDIE ◽  
JOHN N. SOFOS ◽  
KEITH E. BELK ◽  
JOHN A. SCANGA ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Sodium Acetate ◽  
Sensory Quality ◽  
Sodium Lactate ◽  
Hot Water ◽  
Processed Meat ◽  
C Storage ◽  
Heat Treated ◽  
Cured Meat ◽  
Sodium Diacetate

Contamination of ready-to-eat foods, such as frankfurters, with Listeria monocytogenes, is a major concern that needs to be addressed in order to enhance the safety of these products. The objective of this study was to determine the effectiveness of combinations of antimicrobials included in the formulation of frankfurters against L. monocytogenes inoculated (103 to 104 CFU/cm2) on their surface after peeling and before vacuum packaging. In addition, the antilisterial effect of immersing the packaged products, prepared with or without antimicrobials, in hot (75 or 80°C) water for 30 to 90 s was evaluated. Samples were stored at 4°C for up to 120 days and periodically analyzed for pH and for microbial growth on tryptic soy agar plus 0.6% yeast extract (TSAYE) and PALCAM agar. Sodium lactate (1.8%; 3% of a 60% commercial solution) used alone inhibited growth of L. monocytogenes for 35 to 50 days, whereas when used in combination with 0.25% sodium acetate, sodium diacetate, or glucono-δ-lactone (GDL), sodium lactate inhibited growth throughout storage (120 days). Immersing packaged frankfurters in hot water (80°C, 60 s) reduced inoculated populations of L. monocytogenes by 0.4 to 0.9 log CFU/cm2 and reduced its growth by 1.1 to 1.4 log CFU/cm2 at 50 to 70 days of storage in samples containing 1.8% sodium lactate alone. However, immersion of frankfurters containing no antimicrobials in hot water (75 or 80°C) did not inhibit growth of the pathogen for more than 10 to 20 days, unless one frankfurter was placed per bag and heat treated for 90 s. These results indicate that the inclusion of 1.8% sodium lactate with 0.25% sodium acetate, sodium diacetate, or GDL in cured meat formulations may control L. monocytogenes growth during refrigerated (4°C) storage. Additional studies are required to evaluate the effects of these combinations at abusive temperatures of storage, as well as on additional processed meat formulations and on the sensory quality and shelf life of products.

Joining of Dissimilar 6063 Aluminium Alloy – 316L Stainless Steel by Spot Welding: Tensile Shear Strength and Heat Treatment

2013 ◽  
Vol 795 ◽  
pp. 492-495 ◽  
Author(s):  
Mohd Noor Mazlee ◽  
Alvin Tan Yin Zhen ◽  
Shamsul Baharin Jamaludin ◽  
Nur Farhana Hayazi ◽  
Shaiful Rizam Shamsudin
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Shear Strength ◽  
Spot Welding ◽  
316L Stainless Steel ◽  
Welding Current ◽  
Tensile Shear Strength ◽  
Tensile Shear ◽  
Heat Treated ◽  
6063 Aluminum Alloy

Tensile shear strength and ageing treatment of dissimilar 6063 aluminum alloy-316L stainless steel joint fabricated by spot welding were investigated. The results showed that tensile shear strength increased with the increasing of welding current. The enhancement of tensile shear strength of the joints was due to the enlargement of the nugget diameter. It was also found that the tensile shear strength values for heat treated joint almost similar to that of non-heat treated joint.

Problems Associated with Heat Treated Parts

2021 ◽  
pp. 307-325
Author(s):  
Jon L. Dossett
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Cold Working ◽  
Heat Treating ◽  
Heat Treatments ◽  
Quenching Media ◽  
Heat Treated ◽  
Nonferrous Alloys

Abstract This article introduces some of the general sources of heat treating problems with particular emphasis on problems caused by the actual heat treating process and the significant thermal and transformation stresses within a heat treated part. It addresses the design and material factors that cause a part to fail during heat treatment. The article discusses the problems associated with heating and furnaces, quenching media, quenching stresses, hardenability, tempering, carburizing, carbonitriding, and nitriding as well as potential stainless steel problems and problems associated with nonferrous heat treatments. The processes involved in cold working of certain ferrous and nonferrous alloys are also covered.

Biocompatibility Comparison of Stainless Steel, Gold-Coated, and Heat-Treated Gold-Coated Endovascular Stents

2001 ◽  
Vol 711 ◽  
Author(s):  
Alisa S. Morss ◽  
Philip Seifert ◽  
Adam Groothius ◽  
Danielle Bornstein ◽  
Campbell Rogers ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Surface Roughness ◽  
Stainless Steel ◽  
Inflammatory Response ◽  
Neointimal Hyperplasia ◽  
Vascular Response ◽  
Gold Coating ◽  
Endovascular Stents ◽  
Heat Treated ◽  
Negative Effect

ABSTRACTEndovascular stents can be altered to improve radioopacity by applying a gold coating. We examined the vascular response in porcine coronary arteries to implantation of 9 mm NIR® stents that were either left intact, gold-coated, or heat-treated following gold coating. Our results show that while gold coating exacerbates neointimal hyperplasia and the inflammatory response, heat treatment removes this negative effect. Heat treatment was shown to increase the diffusion at the gold-steel interface and reduce the surface roughness.

scholarly journals Evaluation of Heat-Treated AISI 316 Stainless Steel in Solar Furnaces to Be Used as Possible Implant Material

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 581
Author(s):  
Ioan Milosan ◽  
Monica Florescu ◽  
Daniel Cristea ◽  
Ionelia Voiculescu ◽  
Mihai Alin Pop ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
Solar Energy ◽  
Heat Treatments ◽  
Solar Furnace ◽  
316 Stainless Steel ◽  
Heat Treated ◽  
Aisi 316 Stainless Steel ◽  
Aisi 316

The appropriate selection of implant materials is very important for the long-term success of the implants. A modified composition of AISI 316 stainless steel was treated using solar energy in a vertical axis solar furnace and it was subjected to a hyper-hardening treatment at a 1050 °C austenitizing temperature with a rapid cooling in cold water followed by three variants of tempering (150, 250, and 350 °C). After the heat treatment, the samples were analyzed in terms of hardness, microstructure (performed by scanning electron microscopy), and corrosion resistance. The electrochemical measurements were performed by potentiodynamic and electrochemical impedance spectroscopy in liquids that simulate biological fluids (NaCl 0.9% and Ringer’s solution). Different corrosion behaviors according to the heat treatment type have been observed and a passivation layer has formed on some of the heat-treated samples. The samples, heat-treated by immersion quenching, exhibit a significantly improved pitting corrosion resistance. The subsequent heat treatments, like tempering at 350 °C after quenching, also promote low corrosion rates. The heat treatments performed using solar energy applied on stainless steel can lead to good corrosion behavior and can be recommended as unconventional thermal processing of biocompatible materials.

scholarly journals Microstructure of laser metal deposited duplex stainless steel: Influence of shielding gas and heat treatment

2020 ◽  
Author(s):  
Maria Asuncion Valiente Bermejo ◽  
Karthikeyan Thalavai Pandian ◽  
Björn Axelsson ◽  
Ebrahim Harati ◽  
Agnieszka Kisielewicz ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Duplex Stainless Steel ◽  
Nitrogen Loss ◽  
Steel Wire ◽  
Research Work ◽  
Shielding Gas ◽  
Austenite Content ◽  
Heat Treated ◽  
Phase Balance

AbstractThis research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components.

Effect of post-weld heat treatment on thermal diffusivity in UNS S32304 duplex stainless steel welds

2017 ◽  
Vol 2 (88) ◽  
pp. 49-58
Author(s):  
E.G. Betini ◽  
C.S. Mucsi ◽  
T.S. Luz ◽  
M.T.D. Orlando ◽  
M-N. Avettand-Fènoël ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Thermal Diffusivity ◽  
Duplex Stainless Steel ◽  
Welding Process ◽  
Austenite Phase ◽  
Shielding Gas ◽  
Heat Treated ◽  
Steel Welds ◽  
Weld Heat

Purpose: The thermal diffusivity variation of UNS S32304 duplex stainless steel welds was studied after pulsed GTA welding autogenous process without filler addition. This property was measured in the transverse section of thin plates after welding process and post-heat treated at 750°C for 8 h followed by air-cooling. Design/methodology/approach: The present work reports measurements of thermal diffusivity using the laser-flash method. The thermal cycles of welding were acquired during welding by means of k-type thermocouples in regions near the weld joint. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The temperature profiles were obtained using a digital data acquisition system. Findings: It was found an increase of thermal diffusivity after welding process and a decrease of these values after the heat treatment regarding the solidified weld pool zone, irrespective of the welding protection atmosphere. The microstructure was characterized and an increase of austenite phase in the solidified and heat-affected zones was observed for post-weld heat-treated samples. Research limitations/implications: It suggests more investigation and new measurements about the influence of the shielding gas variation on thermal diffusivity in the heat-affected zone. Practical implications: The nuclear industry, especially, requests alloys with high thermal stability in pipes for power generation systems and safe transportation equipment’s for radioactive material. Thus, the duplex stainless steel grades have improved this stability over standard grades and potentially increase the upper service temperature reliability of the equipment. Originality/value: After heat treatment, the welded plate with 98%Ar plus 2%N2 as shielding gas presented a thermal diffusivity closer to the as received sample. By means of 2%-nitrogen addition in shielding gas during GTAW welding of duplex stainless steel may facilitate austenite phase reformation, and then promotes stability on the thermal diffusivity of duplex stainless steels alloys.

Microstructure and Properties of Heat-Treated 440C Martensitic Stainless Steel

2013 ◽  
Vol 334-335 ◽  
pp. 105-110 ◽  
Author(s):  
Siti Hawa Mohamed Salleh ◽  
Mohd Nazree Derman ◽  
Mohd Zaidi Omar ◽  
Junaidi Syarif ◽  
S. Abdullah
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Stainless Steel ◽  
Martensitic Stainless Steel ◽  
Ferrite Matrix ◽  
Rapid Quenching ◽  
Heat Treated Sample ◽  
Treatment Processes ◽  
Heat Treated ◽  
Treated Sample

440C martensitic stainless steels are widely used because of their good mechanical properties. The mechanical properties of 440C martensitic stainless steel were evaluated after heat treatment of these materials at various types of heat treatment processes. The initial part of this investigation focused on the microstructures of these 440C steels. Microstructure evaluations from the as-received to the as-tempered condition were described. In the as-received condition, the formations of ferrite matrix and carbide particles were observed in this steel. In contrast, the precipitation of M7C3carbides and martensitic structures were present in this steel due to the rapid quenching process from the high temperature condition. After precipitation heat treatment, the Cr-rich M23C6carbides were identified within the structures. Moreover, a 30 minutes heat-treated sample shows the highest value of hardness compared to the others holding time. Finally, the tempering process had been carried out to complete the whole heat treatment process in addition to construct the secondary hardening phenomenon. It is believed that this phenomenon influenced the value of hardness of the 440C steel.

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