File Name: bacterial nutrition and growth .zip
Last Updated on January 9, by Sagar Aryal. The microbial cell is made up of several elements such as carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, and iron.
All microbes have a need for three things: carbon, energy, and electrons. There are specific terms associated with the source of each of these items, to help define organisms. Let us focus on carbon first. All organisms are carbon-based with macromolecules — proteins, carbohydrates, lipids, nucleic acid — having a fundamental core of carbon.
Evolution of bacteria
USA info metergroup. In , William James Scott showed that microbial growth in food is governed not by water content , as most people thought, but by water activity. Four years later, he established the concept of a minimum water activity for microbial growth. Water activity is now routinely used by food manufacturers to determine whether or not a product is susceptible to microbial proliferation. The microbial growth limits he and his colleagues established apply to dried meats , cheesecake, powdered drink mix , and dog food , but also to non-food products like tree bark, hand lotion , and insulation.
Like all organisms, microorganisms rely on available water in food for growth. They take up water by moving it across the cell membrane. This water movement mechanism depends on a water activity gradient—on water moving from a high water activity environment outside the cell to a lower water activity environment within the cell.
When water activity outside the cell becomes low enough, it causes osmotic stress: the cell cannot take up water and becomes dormant. The microorganisms are not eliminated, they just become unable to grow enough to cause infection. Different organisms cope with osmotic stress in different ways. Some types of molds and yeasts have adapted to withstand very low water activity levels.
Table 1 shows water activity growth limits for many common microorganisms. If you measure the water activity of any material, you will know which bacteria, molds, or fungi can grow on and in it. By reducing water activity , you can rule out the growth of certain classes of microbes. At low water activities you can preclude the growth of anything at all. Water activity is not a kill step. While temperature, pH , and several other factors can influence whether an organism will grow in a food product and the rate at which it will grow, water activity may be the most important factor.
Most bacteria, for example, do not grow at a water activity range below 0. Water activity in combination with other hurdles , such as pH, temperature, or modified atmosphere packaging, will limit microbial growth even at water activities higher than 0. Everyone knows water activity is related to microbial growth. But how can you use that knowledge to your advantage in formulation, specification, production, and packaging?
In this minute webinar, learn:. Learn everything about how water activity can increase your profit and improve product quality and safety—all in one place. Contact us. No calibration, no approximation. Learn more about how to use hurdles to prevent microbial growth even at water activities higher than 0.
Language Deutsch English. Contact USA info metergroup. Water activity is routinely used by manufacturers to determine whether or not a product is susceptible to microbial growth. Stay current on compliance regulations and water activity measurements in your products. Learn more. Combine water activity with other hurdles Learn more about how to use hurdles to prevent microbial growth even at water activities higher than 0. Read the article. Measure yield and waste in real time. How water activity and pH work together to control microbial growth.
Cosmetics and water activity: achieve quality customers demand. Water activity: a better moisture metric for pet food. Need help? Escherichia coli Clostridium perfringens Salmonella spp. Vibrio cholerae. Penicillium expansum Penicillium islandicum Penicillium viridicatum.
11: Microbial Nutrition
A characteristic of microorganisms is their ability to grow and form a population of organisms. One of the results of microbial metabolism is an increase in the size of the cell. The many requirements for successful growth include those both chemical and physical. Chemical requirements. In order to grow successfully, microorganisms must have a supply of water as well as numerous other substances including mineral elements, growth factors, and gas, such as oxygen. Perhaps 50 percent of a bacterium's dry weight is carbon.
Growth Requirements (pp. ) Microbial growth depends on the metab olism of nutrients, and results in the formation of a discrete colony, an aggregation of cells arising from a single parent cell. A nutrient is any chemical required for growth of microbial populations.
Microbial Growth and Nutrition
Microbial cytoplasm is contained within the cytoplasmic membrane and includes the cytosol, macromolecules, and inclusions. The bacterial cytoplasmic membrane plays a role in permeability and energy conservation in microbial cell structure. The cytoplasmic membranes in bacteria are composed of a phospholipid bilayer; this layer differs from those found in eukaryotes in their lack of sterols. The membranes however, may contain compounds called hopanoids and various fatty acids as well.
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USA info metergroup. In , William James Scott showed that microbial growth in food is governed not by water content , as most people thought, but by water activity.
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