Spores heat-resistant

Many micro-organisms produce nonlinear survivor curves, such as 1-B in Figure 1. The cause of nonlinear survivor curves has been explained by several theories, such as the multiple critical sites theory [9], experimental artifacts [10], and the heterogeneity of spore heat resistance [11]. Mathematical models for concave survivor curves have been developed by Han et al. [12], They are quite... 

The estabhshment of safe thermal processes for preserving food in hermetically sealed containers depends on the slowest heating volume of the container. Heat-treated foods are called commercially sterile. Small numbers of viable, very heat-resistant thermophylic spores may be present even after heat treatment. Thermophylic spores do not germinate at normal storage temperatures. 

Thermoduric, Thermophilic, andPsychrophihc Bacteria. Thermoduric bacteria survive but do not grow at pasteurization temperatures. They are largely non spore-forming, heat-resistant types that develop on surfaces of unclean equipment. These bacteria are determined by subjecting a sample to laboratory pasteurization and examining it by the agar plate method. 

Bradbury, J.H., Foster, J.R., Hammer, B., Lindsay, J. Murrell, W.G. (1981). The source of heat resistance of bacterial spores. Study of water in spores by NMR. Biochimica Biophysica Acta, 678, 157-64. 

Another feature ofthe spore is the presence of pyridine 2,6-dicarboxylic acid (DPA) (Fig. 1.10) occurring as a complex with calcium, which at one time was implicated in heat resistance. The isolation of heat-resistant spores containing no Ca-DPA has refuted this hypothesis. 

The reason for heat resistance is thought to lie in the fact that the core or spore cytoplasm becomes dehydrated during sporulation. The mechanism for this dehydration... 

Again, bacterial spores are much more resistant than vegetative cells, and their recorded resistance varies markedly depending upon their degree of dryness. In many early studies on dry heat resistance of spores their water content was not adequately controlled, so conflicting data arose regarding the exposure conditions necessary to achieve effective sterilization. This was partly responsible for variatiorrs in recommended exposure temperatures and times in different pharmacopoeias. 

John Needham (1713-1781). Similar experiments carried out by an English scientist, John Needham, gave conflicting results. Life developed in Needham s heated closed vessels as well as in the open unheated ones. He therefore believed in spontaneous generation. We shall see later that this result was due to insufficient heating which failed to kill heat-resistant forms of bacteria called spores. But nothing was known about spores at that time. 

When a spore prepares itself for germination, it loses its refractility,Which coincides with an imbibition of water. This stage is associated with a loss in heat resistance, stainability, and dry weighit. Later the spore coat breaks, followed by the emergence from the spore case of a new germ cell which eventually matures into a vegetative cell. 

It has been known for some time that certain types of bacteria spend a certain amount of their lifespan in a dormant state. The bacteria are then known as en-dospores , or just spores . In this state, they appear not to undergo any metabolic processes and are important particularly because of their heat resistance. The formation of spores is a highly complex process of bacterial cell differentiation. 

Heat-resistant fibers, 23 389 Heat-resistant spores, inactivation of, 22 79... 

Similar results were obtained in a study of the combined effect of ultrasound (20 kHz) and heat treatment on the survival of two strains of Bacillus subtilis in distilled water, glycerol and milk [17]. When spores, suspended in water or milk, were subjected to ultrasonic waves before heat treatment little or no decrease of the heat resistance was observed. However when heat and ultrasound were applied simultaneously the heat treatment times in milk were reduced by 74% for B. subtilis var, niger-40 and by 63 % for B. subtilis var, ATCC 6051 and similar results were obtained in glycerol. Thermosonication in water was more marked reducing the heat resistance of the spores by up to 99.9 % in the 70 - 95 °C range. The effect of thermosonication was slightly diminished to 75 % as the temperature reached the boiling point of water. 

The most frequently utilized to challenge moist heat sterilization cycles are Bacillus stearothermophilus and Clostridium sporogenes, spore-forming bacteria are selected because of their relatively high heat resistance. In addition to the selection of an appropriate organism for use as a biological indicator, the concentration and resistance of the indigenous microbial population is established. 

Spore bioburden data are collected to screen for heat-resistant organisms. Organisms surviving heat-resistance testing are to be submitted to the terminal sterilization laboratory for D-value analysis. D-values are then compared to established models for the component sterilization process. 

Thermal Preservation Technology. The heat preservation of foods can he accomplished by various combinations of heating limes and temperatures, depending on the number and type of heat-resistant spores present, the composition of the food, and the physical characteristics of the food and package. 

The inactivation of heat-resistant spores appears lo follow first-order kinetics. Thus if the rate of inactivation of a spun population is knuwn at several temperatures, and the rate or heating of the slowest point in u package can be determined or calculated from heat-transfer principles, then the time needed to sterilize the package can be calculated for any external healing condition. 

Heat is the most widely used means of sterilization, which can be employed for both liquid medium and heatable solid objects. It can be applied as dry or moist heat (steam). The moist heat is more effective than the dry heat, because the intrinsic heat resistance of vegetative bacterial cells is greatly increased in a completely dry state. As a result the death rate is much lower for the dry cells than for moist ones. The heat conduction in dry air is also less rapid than in steam. Therefore, dry heat is used only for the sterilization of glassware or heatable solid materials. By pressurizing a vessel, the steam temperature can be increased significantly above the boiling point of water. Laboratory autoclaves are commonly operated at a steam pressure of about 30 psia, which corresponds to 121°C. Even bacterial spores are rapidly killed at 121 °C. 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

The culture media used in fermentation processes contains a variety of unwanted cells and spores which need to be inactivated or removed before fermentation. The most commonly used inactivation method is heat sterilization. Most cells and some spores can be destroyed at60°C-80°C, while some heat-resistant spores such as bacterial spores require more than 120°C. Heat-based methods, however, cannot be used when the product molecules, such as vitamins and antibiotics, are heat sensitive, because the application of high temperatures changes their properties. In these cases, sterile filtration with membrane filters or depth filters is used. 

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