Cell metabolic activity resumes and the endospore

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Unformatted text preview: d ruptures. Ultimately, the core is released and develops into an vegetative cell. FOOD-290 Endospores and food-poisoning Ingesting the endospores of those bacteria that cause food poisoning can result in either food bourne infection or intoxication: Endospores in food Endospores in food Eaten Germinate in food Germinate in intestine Vegetative cells Vegetative cells Make exotoxin Make exotoxin Food bourne infection Toxin eaten Food bourne intoxication For example, B. cereus is notorious for causing food bourne intoxication as the result of consuming reheated rice. Dry, uncooked rice frequently contains endospores of the soil bacterium B. cereus. When the rice is first cooked, the endospores survive boiling. If cooked rice is left overnight at room temperature in the rice pot any endospores germinate and vegetative cells produce an exotoxin causing food bourne intoxication when the rice is eaten the next day. Reheating the rice before serving does not denature the exotoxin because it is stable to cooking temperatures (Table 9-2). 9.5 Food-spoilage There are two main ways which heterotrophic bacteria cause food spoilage: Extracellular enzyme production Some food spoilage bacteria produce extracellular enzymes such as proteases and lipases which degrade proteins and lipids (fats). Erwinia carotovora(= carrot eater) produces an extracellular pectinase which is associated with spoilage of carrots. Because this enzyme degrades pectin in plant cell walls, this leads to mushy/rubbery carrots. End products of fermentation Some food spoilage bacteria produce organic acids and alcohols as end products of their fermentative metabolism and these produce deleterious changes in the flavour and properties of food (eg. milk souring). FOOD-291 9.6 Control of bacterial growth in the food industry Definitions A bacteriostatic treatment is one designed to inhibit the growth of bacterial cells. Bacteriostatic agents do not kill bacteria; once the agent is removed, the bacteria resume growth. A bacteriociodal treatment is one designed to kill bacterial cells. Bacteriocidal treatments can lead to either sterilization or disinfection. Sterilization refers to the killing of all microorganisms present. Sterilizing agents are called sterilants. Disinfection refers to the killing of all disease-causing microorganisms and a general reduction in the numbers of all other types of microorganisms. If used on inanimate surfaces, agents used in disinfection are called disinfectants; if used on body surfaces these agents are referred to as antiseptics. Treatments Bacteriocidal Kills Sterilization The killing of all microorganisms present Bacteriostatic Inhibits growth Disinfection The killing of all disease-causing microorganisms and a general reduction in the numbers of all other types In modern commercial food production, spoilage and contamination by bacteria that cause food-bourne illness are prevented by numerous methods based on fundamental principles of physics and chemistry that limit microbial growth (Chapter 8). In the food industry, bacterial growth is controlled by manipulating environmental varia...
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This note was uploaded on 10/25/2013 for the course MICB 201 taught by Professor Davidturner during the Fall '12 term at UBC.

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