Promoting Bacillus cereus Spore Germination for Subsequent Inactivation by Mild Heat Treatment

2011 ◽  
Vol 74 (12) ◽  
pp. 2079-2089 ◽  
Author(s):  
IRENE STRANDEN LØVDAL ◽  
MARIA BEFRING HOVDA ◽  
PER EINAR GRANUM ◽  
JAN THOMAS ROSNES
Keyword(s):  
Heat Treatment ◽  
Bacillus Cereus ◽  
Spore Germination ◽  
Heat Inactivation ◽  
Mild Heat ◽  
Heat Treated ◽  
Conventional Heat Treatment ◽  
Heat Activation ◽  
Treatment Procedures ◽  
Double Heat Treatment

Sublethal heat treatment may activate dormant spores and thereby potentiate the conversion of spores to vegetative cells. As the germinated spore is known to possess lower heat resistance than its dormant counterpart, it has been postulated that double heat treatment, i.e., spore heat activation followed by germination and then by heat inactivation, can be used to control spores in foods. Production of refrigerated processed foods of extended durability often includes more than one heat treatment of the food components. This work simulates conventional heat treatment procedures and evaluates double heat treatment as a method to improve spore control in model food matrixes of meat broth and cream sauce. Bacillus cereus NVH 1230-88 spores were supplemented in food model matrixes and heat activated at 70°C and then heat inactivated at 80 or 90°C. The samples were held at 29 to 30°C for 1 h between primary and secondary heat treatments, to allow spore germination. Nutrients naturally present in the food matrixes, e.g., amino acids and inosine, could act as germinants that induce germination. The levels of germinants could be too low to produce effective germination within 1 h. Following primary heat treatment, some samples were therefore supplemented with a combination of L-alanine and inosine, a germinant mixture known to be effective for B. cereus spores. In both matrixes, a combination of double heat treatment (heat activation, germination, and inactivation) and addition of germinants gave a reduction in spore counts equivalent to or greater than that obtained with a single heat treatment for 12 min at 90°C. Addition of germinants was essential to induce effective germination in cream sauce during 1 h at 29 to 30°C, and germinants were therefore a crucial supplement to obtain an effect of double heat treatment in this matrix. These data will be valuable when setting up temperature-time-germinant combinations for an optimized spore reduction in mild-heat–treated foods.

scholarly journals Heat activation and inactivation of bacterial spores. Is there an overlap?

2021 ◽  
Author(s):  
Juan Wen ◽  
Jan P.P.M. Smelt ◽  
Norbert O.E. Vischer ◽  
Arend D Vos ◽  
Peter Setlow ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Spore Germination ◽  
Bacterial Spores ◽  
Heat Inactivation ◽  
Bacillus Species ◽  
Dependent Manner ◽  
Single Spore ◽  
Heat Damage ◽  
Germination Process ◽  
Heat Activation

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80 degrees Celcius, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70 degrees Celcius promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65 degrees Celcius, respectively. 3) Heat inactivation of dormant spores appeared at 70 degrees Celcius, and the heat damage of molecules essential for germination and growth began at 70 and 65 degrees Celcius, respectively. 4) Heat treatment at 75 degrees Celcius resulted in both activation of germination and damage to the germination apparatus, and 80 degrees Celcius treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth.

scholarly journals Heat activation and inactivation of bacterial spores. Is there an overlap?

2022 ◽  
Author(s):  
Juan Wen ◽  
Jan P. P. M. Smelt ◽  
Norbert O.E. Vischer ◽  
Arend L. de Vos ◽  
Peter Setlow ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Spore Germination ◽  
Bacterial Spores ◽  
Heat Inactivation ◽  
Dependent Manner ◽  
Single Spore ◽  
Heat Damage ◽  
Heat Resistant ◽  
New Information ◽  
Heat Activation

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65°C, respectively. 3) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. 4) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. Importance Bacterial spores are thermal resistant structures that can thus survive preservation strategies and revive through the process of spore germination. The more heat resistant spores are the more heterogeneous they germinate upon adding germinants. Upon germination spores can cause food spoilage and cause food intoxication. Here we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.

scholarly journals Germination, Outgrowth, and Vegetative-Growth Kinetics of Dry-Heat-Treated Individual Spores ofBacillusSpecies

2018 ◽  
Vol 84 (7) ◽  
Author(s):  
Lin He ◽  
Zhan Chen ◽  
Shiwei Wang ◽  
Muying Wu ◽  
Peter Setlow ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Spore Germination ◽  
Differential Interference Contrast Microscopy ◽  
Content Type ◽  
Dry Heat ◽  
Heat Treated ◽  
Contrast Microscopy ◽  
Interference Contrast Microscopy ◽  
Dry Heat Treatment ◽  
Kinetics Of

ABSTRACTDNA damage kills dry-heated spores ofBacillus subtilis, but dry-heat-treatment effects on spore germination and outgrowth have not been studied. This is important, since if dry-heat-killed spores germinate and undergo outgrowth, toxic proteins could be synthesized. Here, Raman spectroscopy and differential interference contrast microscopy were used to study germination and outgrowth of individual dry-heat-treatedB. subtilisandBacillus megateriumspores. The major findings in this work were as follows: (i) spores dry-heat-treated at 140°C for 20 min lost nearly all viability but retained their Ca2+-dipicolinic acid (CaDPA) depot; (ii) in most cases, dry-heat treatment increased the average times and variability of all major germination events inB. subtilisspore germination with nutrient germinants or CaDPA, and in one nutrient germination event withB. megateriumspores; (iii)B. subtilisspore germination with dodecylamine, which activates the spore CaDPA release channel, was unaffected by dry-heat treatment; (iv) these results indicate that dry-heat treatment likely damages spore proteins important in nutrient germinant recognition and cortex peptidoglycan hydrolysis, but not CaDPA release itself; and (v) analysis of single spores incubated on nutrient-rich agar showed that while dry-heat-treated spores that are dead can complete germination, they cannot proceed into outgrowth and thus not to vegetative growth. The results of this study provide new information on the effects of dry heat on bacterial spores and indicate that dry-heat sterilization regimens should produce spores that cannot outgrow and thus cannot synthesize potentially dangerous proteins.IMPORTANCEMuch research has shown that high-temperature dry heat is a promising means for the inactivation of spores on medical devices and spacecraft decontamination. Dry heat is known to killBacillus subtilisspores by DNA damage. However, knowledge about the effects of dry-heat treatment on spore germination and outgrowth is limited, especially at the single spore level. In the current work, Raman spectroscopy and differential interference contrast microscopy were used to analyze CaDPA levels in and kinetics of nutrient- and non-nutrient germination of multiple individual dry-heat-treatedB. subtilisandBacillus megateriumspores that were largely dead. The outgrowth and subsequent cell division of these germinated but dead dry-heat-treated spores were also examined. The knowledge obtained in this study will help understand the effects of dry heat on spores both on Earth and in space, and indicates that dry heat can be safely used for sterilization purposes.

Influence of Thermal Exposure on the Structure and Phase Composition of Aluminized Layer Obtained by Explosion Welding and Hot-Dipping Process

2019 ◽  
Vol 946 ◽  
pp. 298-303
Author(s):  
Victor Georgievich Shmorgun ◽  
Dmitriy Vladimirovich Pronichev ◽  
V.P. Kulevich
Keyword(s):  
Heat Treatment ◽  
Diffusion Zone ◽  
Main Crack ◽  
Steel Surface ◽  
Thermal Exposure ◽  
Explosion Welding ◽  
Intermetallic Coating ◽  
Heat Treated ◽  
Dipping Process ◽  
Double Heat Treatment

It is shown that for the formation of Fe2Al5 intermetallic coatings on the steel surface the aluminized layer obtained by explosion welding must be subjected to a double heat treatment (660 °C, 3 h + 640 °C, 3 h). The first heat treatment ensures the necessary size of the diffusion zone, and the second leads to the formation of a main crack at the interface of Fe2Al5 and FeAl3 intermetallides, which allows to separate the unreacted layer of aluminum and form a coating with hardness of 10 GPa. To form Fe2Al5 intermetallic coating on the steel surface, the aluminized layer, which is immersed in the melt, must be heat treated at 800 °C. The alloying of the diffusion zone by Si and Cu with the replacement of aluminum by the AK12M2 alloy leads to a decrease in the thickness of the diffusion zone and the appearance of additional phases of Al7Fe2Si and (Al,Si)5Fe3 in its composition. The duration of the subsequent heat treatment at 800 °C for complete dissolution of the surface layer increases the hardness of the resulting coating on the basis of a solid solution of Si in Fe2Al5 is 7.5-8 GPa.

scholarly journals Analysis of Germination Capacity and Germinant Receptor (Sub)clusters of Genome-Sequenced Bacillus cereus Environmental Isolates and Model Strains

2016 ◽  
Vol 83 (4) ◽  
Author(s):  
Alicja K. Warda ◽  
Yinghua Xiao ◽  
Jos Boekhorst ◽  
Marjon H. J. Wells-Bennik ◽  
Masja N. Nierop Groot ◽  
...  
Keyword(s):  
Bacillus Cereus ◽  
Spore Germination ◽  
Brain Heart Infusion ◽  
Whole Genome Sequence ◽  
Single Spore ◽  
Content Type ◽  
Germination Response ◽  
Natural Isolates ◽  
Heat Activation ◽  
Different Strains

ABSTRACT Spore germination of 17 Bacillus cereus food isolates and reference strains was evaluated using flow cytometry analysis in combination with fluorescent staining at a single-spore level. This approach allowed for rapid collection of germination data under more than 20 conditions, including heat activation of spores, germination in complex media (brain heart infusion [BHI] and tryptone soy broth [TSB]), and exposure to saturating concentrations of single amino acids and the combination of alanine and inosine. Whole-genome sequence comparison revealed a total of 11 clusters of operons encoding germinant receptors (GRs): GerK, GerI, and GerL were present in all strains, whereas GerR, GerS, GerG, GerQ, GerX, GerF, GerW, and GerZ (sub)clusters showed a more diverse presence/absence in different strains. The spores of tested strains displayed high diversity with regard to their sensitivity and responsiveness to selected germinants and heat activation. The two laboratory strains, B. cereus ATCC 14579 and ATCC 10987, and 11 food isolates showed a good germination response under a range of conditions, whereas four other strains (B. cereus B4085, B4086, B4116, and B4153) belonging to phylogenetic group IIIA showed a very weak germination response even in BHI and TSB media. Germination responses could not be linked to specific (combinations of) GRs, but it was noted that the four group IIIA strains contained pseudogenes or variants of subunit C in their gerL cluster. Additionally, two of those strains (B4086 and B4153) carried pseudogenes in the gerK and gerR I (sub)clusters that possibly affected the functionality of these GRs. IMPORTANCE Germination of bacterial spores is a critical step before vegetative growth can resume. Food products may contain nutrient germinants that trigger germination and outgrowth of Bacillus species spores, possibly leading to food spoilage or foodborne illness. Prediction of spore germination behavior is, however, very challenging, especially for spores of natural isolates that tend to show more diverse germination responses than laboratory strains. The approach used has provided information on the genetic diversity in GRs and corresponding subclusters encoded by B. cereus strains, as well as their germination behavior and possible associations with GRs, and it provides a basis for further extension of knowledge on the role of GRs in B. cereus (group member) ecology and transmission to the host.

Optimized Thermomechanical Treatment for Strong and Ductile Martensitic Steels

2007 ◽  
Vol 539-543 ◽  
pp. 4526-4531 ◽  
Author(s):  
Araz Ardehali Barani ◽  
Dirk Ponge
Keyword(s):  
Heat Treatment ◽  
Thermomechanical Treatment ◽  
Spring Steel ◽  
Martensitic Steels ◽  
Medium Carbon ◽  
Heat Treated ◽  
Conventional Heat Treatment ◽  
The Matrix ◽  
Different Levels ◽  
Strength And Ductility

In this study the effect of thermomechanical treatment on the microstructure of austenite and martensite and the mechanical properties of a medium carbon silicon chromium spring steel with different levels of impurities is investigated. Results are presented for conventional heat treatment and for thermomechanical treatment (TMT). Compared to conventionally heat treated samples austenite deformation improves strength and ductility. Thermomechanically treated samples are not prone to embrittlement by phosphorous. TMT influences the shape and distribution of carbides within the matrix and at prior austenite grain boundaries. It is shown that utilization of TMT is beneficial for increasing the ultimate tensile strength to levels above 2200 MPa and at the same time maintaining the ductility obtained at strength levels of 1500 MPa by conventional heat treatment. The endurance limit is increased and embrittlement does not occur.

scholarly journals EFFECT OF HEAT TREATMENT AND PLASMA NITRIDING ON CORROSION RESISTANCE OF 440B MARTENSITIC STAINLESS STEEL

2013 ◽  
Vol 7 (3) ◽  
pp. 155-159 ◽  
Author(s):  
Magdalena Łępicka ◽  
Małgorzata Grądzka-Dahlke
Keyword(s):  
Heat Treatment ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
Plasma Nitriding ◽  
Steel Corrosion ◽  
Surgical Instruments ◽  
High Wear Resistance ◽  
Heat Treated ◽  
Conventional Heat Treatment ◽  
Steel Corrosion Resistance

Abstract Reliability and durability assurance poses a serious challenge for surgical instruments manufacturers. Hard working conditions, such as intermittent contact with body fluids and hard bone tissues, as well as necessity to undergo frequent sterilisation processes, induce constant research into solutions capable of ensuring high wear resistance while maintaining satisfactory imperviousness to corrosion. Plasma nitriding is marked as the modern corrosion resistance improving method suitable for surgical instruments steels. The paper presents findings from the heat treated and plasma nitrided AISI 440B (PN EN or DIN X90CrMoV18) steel corrosion resistance studies. Three conventionally heat treated (quenched with tempering in 250, 390 or 605°C) and three additionally plasma nitrided in N2:H2 reaction gas mixture (50:50, 35:65 and 20:80 ratio, respectively) specimens groups were examined. Furthermore, the authors evaluated the effect of machining - polishing and sandblasting - on investigated steel corrosion resistance. Microscopic observations and electrochemical corrosion tests were performed using a variety of analytical techniques. Results showed that, in comparison to conventional heat treatment, plasma nitriding of 440B stainless steel does not significantly affect its corrosive characteristics as far as the uniform nitride layer over the entire detail surface is obtained. The layer heterogeneity results in intensification of corrosion processes, making the material even more susceptible to corrosion than after conventional heat treatment, and contributing to severe, visible even with the unaided eye damages development.

Effect of non-conventional heat treatment of API X60 pipeline steel on corrosion resistance and stress corrosion cracking susceptibility

2019 ◽  
Vol 66 (3) ◽  
pp. 274-285 ◽  
Author(s):  
Luis Ricardo Jacobo ◽  
Rafael Garcia ◽  
Victor Hugo Lopez ◽  
Antonio Contreras
Keyword(s):  
Heat Treatment ◽  
Corrosion Resistance ◽  
Strain Rate ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Activation Process ◽  
Content Type ◽  
Heat Treated ◽  
Conventional Heat Treatment

Purpose The purpose of this paper is to study the effect of heat treatment (HT) applied to an API X60 steel in corrosion resistance and stress corrosion cracking (SCC) susceptibility through slow strain rate tests (SSRT) in NS4 solution and congenital water (CW) to assess external and internal SCC, respectively. Design/methodology/approach API X60 steel was heat treated at a temperature of 1,200°C for 30 min followed by water quenching. Specimens from this steel were machined according to NACE TM 198. SSRT were performed in a constant extension rate tests (CERT) machine at room temperature at a strain rate of 1 × 10–6 s–1. For this purpose, a glass cell was used. Corrosion behavior was evaluated through polarization curves (PCs). Findings The SCC index obtained from SSRT indicates that the steel heat treated could be susceptible to SCC in CW and NS4 solution; the mechanism of SCC was hydrogen embrittlement. Thus, CW may promote the SCC phenomenon in pipelines. HT improves the steel corrosion resistance. Higher corrosion rate (CR) was observed when the steel is exposed to CW. The corrosion process in X60 steel shows that the oxidation reaction in the anodic branch corresponds to an activation process, and the cathode branches reveal a diffusion process. Originality/value The purpose of the heat treatment applied to X60 steel was to generate a microstructure of acicular ferrite to improve the corrosion resistance and SCC behavior.

Fracture toughness relationships in a low-alloy steel

1983 ◽  
Vol 41 ◽  
pp. 224-225
Author(s):  
R. Padmanabhan ◽  
W. E. Wood
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Plane Strain Fracture Toughness ◽  
Low Alloy Steel ◽  
Heat Treated ◽  
Strain Fracture ◽  
Conventional Heat Treatment ◽  
Microstructural Effects ◽  
Improve Fracture Toughness ◽  
Inverse Response

Utilization of high austenitization temperatures to improve fracture toughness of UHSLA steels at similar strength levels has received considerable interest. However, these heat treatments result in reduced ductility and impact toughness. This inverse response of impact and plane strain fracture toughness is essentially due to microstructural effects and it is possible to achieve simultaneous improvements in all these properties through controlled variations in the microstructure.A vacuum remelted Si-modified 4340 steel was chosen for this study under three heat treated conditions, viz., conventional, high temperature and step with austenitization temperatures of 1143 K (1 hr), 1473 K (1 hr) and 1473 K (1 hr) furnace cooled to 1143 K (5 min), respectively. All samples were quenched in oil and tempered at 553 K (1 hr). A modified conventional heat treatment was also designed to achieve a desired microstructure with a 1143 K (1 hr) austenitization, a 923 K (1 hr) intermediate temper (after oil quenching), a 1123 K (3 min) reaustenitization and a final 553 K (1 hr) temper (after requenching) steps.

THE EFFECT OF HEAT TREATMENT OF MILK UPON THE HYDROLYZABILITY OF LACTOSE BY THE ENZYME LACTASE1

1970 ◽  
Vol 33 (9) ◽  
pp. 377-379 ◽  
Author(s):  
W. L. Wendorff ◽  
C. H. Amundson ◽  
N. F. Olson
Keyword(s):  
Heat Treatment ◽  
Salt Solution ◽  
Milk Protein ◽  
Lactose Hydrolysis ◽  
Additional Heat ◽  
Total Solids ◽  
Heat Treated ◽  
Dry Milk ◽  
Double Heat Treatment ◽  
Spray Dried

Heat treated, condensed skimmilk and nonfat dry milk (NDM) were treated with lactase enzyme obtained from Saccharomyces fragilis. The effect of heat treatment on lactose hydrolysis was determined. Forewarming treatments of 62.8, 68.3, 73.9, 79.5, and 85.0 C resulted in 17, 17, 100, 59, and 156 g, respectively, of lactose hydrolyzed. Concentrates with forewarming treatments of 62.8, 73.9, and 85.0 C for 30 min were given additional heat treatments of 62.8, 73.9, or 85.0 C for 20 min. Activity was lower in all concentrates given the double heat treatment, except those heated at 85.0 C for 20 min after forewarming at 62.8 and 73.9 C. These showed a substantial increase in lactose hydrolysis. Portions of each concentrate, spray dried and reconstituted to 30% total solids, exhibited the same effect on lactose hydrolysis as the original concentrates. Additional studies were conducted with whey and a 5% lactose plus milk salt solution. Results indicated that heating lactose in the presence of milk protein had a great effect on lactose hydrolysis.

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