Learn more: Different forms of DNA (A-DNA, B-DNA and Z-DNA) Ø A-DNA is also comparatively more resistant to the denaturing effects of dry heat. Ø The A-DNA is more compact than B-DNA and thus A-DNA can have higher resistance against pyrimidine dimer formation by UV radiations. Ø The binding of SASPs to the DNA changes the molecular structure of DNA from its normal B-form to A-form. Ø These proteins can bind to the DNA of endospores and can prevent the DNA from heat, radiations and chemicals. Ø Large amounts of Small Acid Soluble DNA binding Proteins (SASPs) are reported to occur in the core of endospores. Ø The calcium-dipicolinic acid can stabilize the genetic materials of the endospores. ![]() Ø High concentration of calcium ions can impart resistance to wet heat and oxidizing agents. Ø This view is now questioned since mutants lacking dipicolinic acid with heat resistance are isolated and this suggests the involvement of other mechanisms. Ø For a long time, it was believed that the high concentration of dipicolinic acid is providing the heat resistance to endospores. Ø The dipicolinic acid in bacterial endospore not occurs in free-state rather, it forms a complex with calcium ions (Ca 2+). Ø In some endospores, about 15% of the total dry weight of the spore is contributed dipicolinic acid. Ø Endospores contain high amount of dipicolinic acid in its core (protoplast). ![]() Some of the possible explanations are given below: Several explanations are now prevailing in the scientific community to explain this. The exact reason for the high resistance of endospores towards extreme temperature, radiation and chemicals is still unknown. Why the Bacterial Endospores are Extremely Resistant to Temperature, Radiations and Chemicals? Ø The core only contains about 10 – 25% of water of the normal vegetative cell. Ø Unlike the vegetative cells, the core protoplast is metabolically inactive. Ø The core contains ribosomes and centrally placed nucleoid (genetic material). Ø The endospore core has a normal cell structure as that of a vegetative cell. Ø Spore cell wall covers the central protoplast or Core of the endospore. Ø The innermost layer of the spore is called the Spore Cell wall or Core Cell Wall. Ø The peptidoglycan in the cortex is less cross linked than that of vegetative cells. Ø The cortex is composed of peptidoglycan Ø Cortex is very large and sometimes occupy as much as half of the spore volume. Ø Cortex is the thicker wall layer in the endospores. All rights reserved.Ø The thickness of the spore coat is one reason for the high resistance of endospores towards heat, radiation and chemicals. This extensively-documented survey of the species that cause non-stability at 55 ☌ in LACF will help canneries to improve the management of microbial contamination.Ĭopyright © 2013 Elsevier B.V. Taken together, our results single out the species most suitable for use as indicators for thermal process settings. The spore heat resistance parameters (D or δ and z values) from 36 strains isolated in this study were determined. vegetables, ready-made meals containing meat, seafood or other recipes, products containing fatty duck, and related to the intensity of the thermal treatment applied in these food categories. Species frequency was dependent on food category, i.e. The other most frequent bacterial genera identified were Bacillus, Thermoanaerobacter, Caldanaerobius, Anoxybacillus, Paenibacillus and Clostridium. ![]() Three genera were responsible for more than 80% of all non-stability cases: mostly Moorella (36%) and Geobacillus (35%), and less frequently Thermoanaerobacterium (10%). A single species was identified for 93% of examined samples. Bacteria were identified by microsequencing or a recent developed tool for group-specific PCR detection (SporeTraQ™). In this study we identified the bacterial species responsible for non-stability after prolonged at 55 ☌ of incubation of LACF from 455 samples collected from 122 French canneries over 10 years. ![]() LACF are also often submitted to additional incubation conditions, typically 55 ☌ for 7 days, to monitor spoilage by thermophiles. Good Manufacturing Hygienic Practices include stability tests for managing the pathogen risk related to surviving mesophilic bacterial spores. Thermal processing of Low Acid Canned Foods (LACF), which are safe and shelf-stable at ambient temperature for several years, results in heat inactivation of all vegetative microorganisms and the partial or total inactivation of spores.
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