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microbes destruction through heat
Typology: Summaries
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Destruction of micro-organisms: Micro- organisms are found everywhere in environment and are capable of adapting themselves to almost every growth condition. Presence of some micro-organisms maybe beneficial as in the production of cheese, pickles, leavening of bread etc, while some are harmful and are associated with food spoilage. Infective types of bacteria, such as Salmonella and Shigella, multiply in the intestinal tract and cause disease through infection of the host. In contrast, bacteria like Staphylococcus aureus and Clostridium botulinum produce the toxins present in the food at the time of consumption and are the direct cause of illness. Food storage under conditions that prevent bacterial growth do not provide safety against infective pathogens, but do so against toxicogenic food poisons. Moulds also produce toxins, the mould Aspergillus flavus produces a toxin, aflatoxin which when present in food is a health hazard.
There are many other moulds producing toxins refer to as mycotoxins. Cooking food to the required length of time can destroy all harmful micro-organisms in foods. One of the most important methods of protection of food against harmful micro- organisms is by the application of heat. Effect of heat on micro-organisms: The application of heat to food is so universal that “processing” and “heating” are considered synonymous. This underlines the importance of heat in bringing about physical, chemical and biological modifications in food. The purpose of heat treatment in food preservation is to kill micro-organisms and to inactivate the enzymes that become active in subsequent storage of packed foods. The complete destruction of micro- organisms is known as sterilization. This is achieved when organisms are exposed at 121° C to wet heat for 15 minutes. This can be accomplished in a pressure cooker or autoclave on a small scale or, on a commercial scale in pressure retorts.
Decimal reduction time, or D-value: It is the time it takes for a microbial population to be reduced by 90% or one logarithmic cycle. It's a measure of how effective a disinfectant is on a surface. Uses: Determines the most common and persistent bacteria in a healthcare facility. Used to select disinfectants for low, intermediate, and high levels. Factors: Determined under specified conditions, such as sterilant concentration,
exposure temperature, relative humidity, and package configuration. The log phase or log cycle: also known as the exponential growth phase, is a period of rapid growth in microorganisms where the number of cells increases exponentially. The phases of the log cycle, or bacterial growth curve, are: Lag phase: The initial phase where cells adapt to their environment and prepare for reproduction. Exponential (log) phase: A phase of rapid cell division, where each cell generation occurs in the same time interval as the previous ones. Stationary phase: A phase where the rate of cell division equals the rate of cell death, due to limited resources. Death phase: A phase where the bacterial population declines due to factors like nutrient depletion or environmental stress. The growth curve can vary from organism to organism, or even with different conditions for the same organism.
D-value by a factor of ten. The Z-value is a measure of how sensitive a microorganism is to changes in temperature by increasing or decreasing the temperature by 1 decimal. A smaller Z-value indicates that the micro- organism is more sensitive to heat. F value: The F value is the amount of time required to kill a specific number of micro- organisms in a food at a given temperature. It is used to designate the time required to destroy a given number of microorganisms at a reference temperature. Advantages and Disadvantages of canning: Preservation of food by canning has various advantages and disadvantages which are, Advantages-