Concentrate processing carrier requirements

Active transport is a carrier-mediated process that requires energy to move molecules against an electrochemical or concentration gradient. It is more important in elimination or secretory processes than for absorption. Only a few drugs, such as o-methyldopa and 5-fluorouacil, are transferred by active transport. 

Absorption of vitamin C from the small intestine is a carrier-mediated process that requires sodium at the luminal surface. Transport is most rapid in the ileum and resembles the sodium-dependent transport of sugars and amino acids, but the carrier is distinct for each class of compound. Some ascorbate may also enter by simple diffusion. With dietary intake less than 100 mg/d, efficiency of absorption is 80-90%. With intake equal to the RDA, plasma ascorbate is 0.7-1.2 mg/dL, and the ascorbate pool size is 1500 mg. Scurvy becomes evident when the pool is less than 300 mg, at which point plasma ascorbate is 0.13-0.24 mg/dL. Highest tissue concentrations of ascorbate are in the adrenal gland (cortex > medulla). 

Prevent/ Mitigate Optimize shipment conditions to minimize potential consequences of release (e.g., temperature, pressure, phase, concentration) Changes in production process and transportation carrier requirements... 

Active transport or pump mechanisms. In this form of transport not only is a specific carrier required but at the same time energy must be expended and, as a result of cellular metabolic activity, materials can be moved uphill , i.e. against a concentration gradient. The energy is provided by ATP and a specific ATPase is required for the process. If this enzyme is blocked or if there is a failure of ATP synthesis, e.g. by the inhibition of oxidative phosphorylation, then active transport is prevented. 

In the design and construction of new production systems, technical specifications play an important role. They represent a company s collective experiences from their production systems in operation. The company s project organisation instructs machinery and equipment vendors and engineering contractors to comply with the requirements in the specifications. We have to interpret the experiences from individual accidents and near accidents and from analyses of accident concentrations and translate them into specific requirements for use in such specifications. It is recommended that group problem-solving techniques be applied in this process. Regulatory requirements and standards on safety are similar experience carriers at the national or branch-of-industry levels. We will come back to this issue in Chapter 27. 

Glucose and galactose enter the absorptive cells by way of secondary active transport. Cotransport carrier molecules associated with the disaccharidases in the brush border transport the monosaccharide and a Na+ ion from the lumen of the small intestine into the absorptive cell. This process is referred to as "secondary" because the cotransport carriers operate passively and do not require energy. However, they do require a concentration gradient for the transport of Na+ ions into the cell. This gradient is established by the active transport of Na+ ions out of the absorptive cell at the basolateral surface. Fructose enters the absorptive cells by way of facilitated diffusion. All monosaccharide molecules exit the absorptive cells by way of facilitated diffusion and enter the blood capillaries. 

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