The heat sensitivity of various micro-organisms is illustrated by Table 4.3 which shows their D values. Generally psychrotrophs are less heat resistant than mesophiles, which are less heat resistant than thermophiles; and Gram-positives are more heat resistant than Gram-negatives.
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Which bacteria produce the most heat-resistant spores?
Bacterial spores are usually far more heat resistant than vegetative cells; thermophiles produce the most heat resistant spores while those of psychrotrophs and psychrophiles are most heat sensitive. Since spore inactivation is the principal concern in producing appertized foods, much higher temperatures are used in appertization processes and in the measurement of spore D …
What is the heat sensitivity of microorganisms?
Jan 05, 2009 · The common etiological agents screened, produced asexual spores (conidiospores) that exhibited high resistance to heat treatment at 80 degrees C. Of the three isolates, E. floccosum, with a decimal reduction time (D-value) of D80 = 4.4 min was the most resistant followed by T. mentagrophytes with D80 = 4.0 min and then T. rubrum with D80 = 3.2 …
Do heating rates affect the thermal resistance of E coli?
A. Albihn, in Encyclopedia of Microbiology (Third Edition), 2009 Heat Treatment. Heat treatment owing to a temperature rise from microbial activity or by way of external supply of energy is a common and safe hygienic treatment, as long as both the temperature and the treatment time are sufficient. The temperature and the time required depend on the type and strain of organism, …
Why are spore molecules so heat resistant?
These bacteria are called thermoduric and include members of the coryneform group, heat-resistant streptococci, micrococci, and spore-forming bacteria. The predominant spore-forming organisms found in heated milk are Bacillus spp., which survive heat …
What microbe is most resistant to heat?
Regarding the most and least resistant pathogens to heat, S. senftenberg 775W, L. monocytogenes and some strains of S. aureus would be the most heat resistant, whereas Campylobacter would be even the least heat-resistant one (Sagarzazu et al., 2010b).May 20, 2016
What microbes are resistant to heat sterilization?
A recent investigation by the author has shown that the aerobic mesophilic bacterial sporeformers, such as Bacillus subtilis and Bacillus coagulans, are the most resistant among several species of sporeforming bacteria to dry heat sterilization.
What is most resistant to microbial control?
Endospores are considered the most resistant structure of microbes. They are resistant to most agents that would normally kill the vegetative cells they formed from. Mycobacterial infections are notoriously difficult to treat. Protozoa cysts are quite hard to eliminate too.Jan 3, 2021
Why are some microorganisms more resistant to heat?
Thermal resistance of microorganisms is affected by many different factors. Some of the most influencing factors are the water activity, nutrient content, pH of the heating medium, growth phase and growth temperature of the microbial culture, as well as the genus, species and even the strain within the same species.Aug 11, 2016
Which microorganisms are most resistant to moist heat sterilization?
The most commonly reported moist heat resistant microorganisms are B. stearothermophilus (reclassified by ATCC to Geobacillus stearothermophilus), B. subtilis variety 5230, C.
What microorganisms are most resistant to disinfectants?
7-9 The most resistant to disinfectants are believed to be the prions,” followed by coccidia, with bacterial spores and mycobacteria being the most resistant types of bacteria (Fig. l).
Which is the most resistant structure in bacteria?
endosporesA variety of different microorganisms form "spores" or "cysts", but the endospores of low G+C Gram-positive bacteria are by far the most resistant to harsh conditions.
Which of the following is most resistant to sterilization process?
Except for prions, bacterial spores possess the highest innate resistance to chemical germicides, followed by coccidia (e.g., Cryptosporidium), mycobacteria (e.g., M.
Which type of bacteria is the most difficult to inactivate?
Different groups of bacteria vary in their susceptibility to biocides, with bacterial spores being the most resistant, followed by mycobacteria, then Gram-negative organisms, with cocci generally being the most sensitive. There are wide divergencies within this general classification.
Which factors are affecting the heat resistance of microorganisms?
Water: Heat resistance of microorganisms increases with decrease in moisture/ water activity and humidity. This is due to faster denaturation of protein in presence of water than air. Fat: Heat resistance increases in presence of fat due to direct effect of fat on cell moisture.
How can you be resistant to heat?
Staying Safe and Healthy. Wear lightweight clothing. Stick to short-sleeved items like t-shirts, shorts, tank tops, and moisture-wicking activewear until you've built up an immunity to the heat. Pieces with loosely-woven materials and more relaxed fits are also preferable, as they'll allow your skin to breathe.
Which type of heat treatment is most effective What is the most likely explanation for one method being more effective than the other?
If so, why? Moist heat is generally more effective than dry heat for killing microorganisms because of its ability to penetrate microbial cells. Moist heat kills microorganisms by denaturing their proteins (causes proteins and enzymes to lose their three-dimensional functional shape).
How does heat treatment affect flour?
Heat treatment of flour is used to change its physical and rheological properties. The heat reduces the elasticity and even denatures the gluten. The starch can be gelatinized and enzymatic activity reduced or eliminated. The heat also causes a reduction in the bacterial count of flour. In terms of amylograph values, a flour viscosity of about 300 Brabender units (BU) could be effected by heat treatment and reach 800 BU. The new characteristics improve the water-holding capacity of the treated flour. The heat-treated flour is used for special end uses such as soups, sausage filling material, infant foods, and other food and nonfood products.
What is multistage heat treatment?
Multistage heat treatments are given to powder metallurgy superalloy products to develop alloy microstructures appropriate for the application. Heat treatment involves a sequence of a solution anneal followed by one or more precipitation aging treatments. The solution anneal is performed to allow carbides and precipitated constituents to go into solid solution. This anneal is usually followed by some type of rapid cooling to prevent dissolution and reprecipitation. Directional heat treatments can be used for ODS alloys to promote the formation of very coarse, elongated grains. These anneals and treatments prepare the alloy for later heat treatments where control of temperature, time, and cooling rate promotes selective precipitation of the various phases to the desired locations in the microstructure. Single or multistage aging treatments are then used to develop the desired precipitate size and size distributions.
How does heat affect lipids?
Heat treatments may affect protein–lipid interactions in terms of free-radical formation, changes in emulsifying capacity, and alteration of conjugated lipoprotein structure . Lipid–protein free radicals may be formed when free radicals produced by oxidation of unsaturated lipids react with proteins. High temperatures greatly increase the rate of oxidation of sulfur-containing amino acids via reactions with oxidized lipids. Cysteine and histidine free-radicals may then cross-link and induce aggregation of proteins. As discussed in the emulsifying capacity section, partial denaturation of globular proteins may expose hydrophobic sites and increase emulsifying capacity, thereby increasing the ability of proteins to interact with lipids; however, higher heat treatments will decrease this ability. Heat also will denature proteins in conjugated lipoprotein structures and affect the functionality of these, especially in membrane systems.
How to free plant material from viruses?
Heat treatment has been a most useful method for freeing plant material from viruses. Many viruses have been eliminated from at least one host plant by heat treatment (Walkey, 1991 ).
What is heat treatment in dairy?
Heat treatment is a common operation in the dairy industry. The most commonly used heat treatments are pasteurization (with low or high intensities), ultra high temperature (UHT) treatment, and sterilization. The aim of these treatments is to destroy pathogens to ensure a safe product. During heating, several biochemical reactions occur like denaturation of whey proteins, Maillard reactions, proteolysis, deamidation, destruction of some vitamins, and alterations of the salt equilibria. These modifications depend on the intensity of the heat treatment. Concerning the salt equilibria, it is known that when the milk temperature increases, the dissociation of inorganic phosphate present in the aqueous phase increases. Consequently, part of H 2 PO 4 - is transformed to HPO 42-, which has a higher affinity for calcium than H 2 PO 4 - and reacts with calcium to form a calcium phosphate salt. The aqueous phase being supersaturated in this salt, the concentrations in calcium and inorganic phosphate are reduced in this phase. The extent of these decreases depends on the intensity of the applied heat treatment. If the heat treatment is less than 95 °C for few minutes, the modifications of salt equilibria are reversible after cooling. If the heat treatment is severe (more than 100 °C for several minutes), alterations of the salt equilibria are irreversible. On the other hand, during intense heat treatments, casein molecules can be dephosphorylated. In these cases, the decreases of calcium and phosphate contents in the aqueous phase do not correspond to a simple precipitation of calcium phosphate. It is noteworthy that for severe heat treatment, some changes in the structure and composition of the MCP are observed. The newly formed phase is not clearly identified but it is related to the formation of crystalline β-tricalcium phosphate or hydroxyapatite.
Why is heat treatment important for metals?
The heat treatment of metallic alloys can be effectively used to obtain the mechanical properties that are desired for the alloy. Many of the phase transformations that occur are controlled by the temperature and time of the heat treatment. The precise control of temperature and time is necessary to produce high-quality parts ...
How does heat affect flour?
Heat treatment of flour is used to change its physical and rheological properties. The heat reduces the elasticity and even denatures the gluten. The starch can be gelatinized and enzymatic activity reduced or eliminated. The heat also causes a reduction in the bacterial count of flour.
What happens during heating?
During heating, several biochemical reactions occur like denaturation of whey proteins, Maillard reactions, proteolysis, deamidation, destruction of some vitamins, and alterations of the salt equilibria.
How does heat treatment affect yogurt?
It allows removing spoilage microorganisms, inactivating lactoperoxidases and producing stimulatory compounds in milk. In parallel, heat treatment contributes to improved yogurt texture by allowing whey protein denaturation and interaction with casein, resulting in a decrease of gel syneresis and an increase of gel firmness. During industrial yogurt manufacture, the mixes are generally heated at 90 or 95 °C for 3–7 min before cooling down to fermentation temperature. Plate heat exchangers, with a tubular holding zone, are generally used and are designed in order to cool the mix accurately at the fermentation temperature (between 37 and 43 °C).
What is blanching vegetables?
Blanching is a heat treatment implemented prior to freezing or canning of vegetables to inactivate enzymes. This treatment provides protection of nutritional and sensorial quality. However, conditions that require inactivating enzymes are different from each other.
What is multistage heat treatment?
Multistage heat treatments are given to powder metallurgy superalloy products to develop alloy microstructures appropriate for the application. Heat treatment involves a sequence of a solution anneal followed by one or more precipitation aging treatments. The solution anneal is performed to allow carbides and precipitated constituents to go into solid solution. This anneal is usually followed by some type of rapid cooling to prevent dissolution and reprecipitation. Directional heat treatments can be used for ODS alloys to promote the formation of very coarse, elongated grains. These anneals and treatments prepare the alloy for later heat treatments where control of temperature, time, and cooling rate promotes selective precipitation of the various phases to the desired locations in the microstructure. Single or multistage aging treatments are then used to develop the desired precipitate size and size distributions.
What are the challenges of compound feed?
One of the biggest challenges in the compound feed industry, in terms of processing, is heat treatments. Everything indicates that we have great opportunities and at the same time great challenges.
How does feed cost affect animal production?
Feed cost is of significant importance in animal production, since it represents around 70% of the cost of live animals or derived products. Therefore, maximizing the use of feed, improving the productive efficiency index by improving feed conversion and reducing the negative impact of microorganisms, is essential for economic and environmental viability. One of the ways to improve this efficiency is through heat treating the feed.