Protein nutrient bioavailability

Experimental Procedures. Nutrient bioavailability is a complex subject when applied to protein components. In fact, it is an error to speak of the bioavailability of the protein rather one must consider the availability of the individual amino acids which make up the protein. Amino acid availability implies sufficient digestion of the protein in the intestines to allow absorption into the tissue. Then, in the case where... 

At low and medium doses, it is well established that the nutritional value of proteins, carbohydrates, and fats as macronutrients are not significantly impaired by irradiation, and neither the mineral bioavailability is impacted. Like all other energy depositing process, the application of ionizing radiation treatment can reduce the levels of certain sensitive vitamins. Nutrient loss can be minimized by irradiating food in a cold or frozen state and under reduced levels of oxygen. Thiamin and ascorbic acid are the most radiation sensitive, water-soluble vitamins, whereas the most sensitive, fat-soluble vitamin is vitamin E. In chilled pork cuts at the 3 kGy maximum at 0-10°C, one may expect about 35 0% loss of thiamin in frozen, uncooked pork meat irradiated at a 7 kGy maximum at —20°C approx., 35 % loss of it can be expected [122]. 

Bioavailability can be influenced directly or indirectly by many physiological, pathological, chemical, nutritional, and processing conditions. Discussion in this chapter will be limited to unit food processing effects upon the bioavailability of nutrients from plant protein foods. The bioavailability of amino acids, carbohydrates, lipids, vitamins and minerals from processed foods will be selectively reviewed. Amino Acids... 

Investigations have focused on the content or polyphenolics. tannins, and related compounds in various foods and the influence on nutrient availability and protein digestibility. It has been established that naturally occurring concentrations ofpolyphcnoloxtda.se and polyphenols in products such as mushrooms can result in reduced iron bioavailability. Likewise, several studies have locused on decreased protein digestibility caused hy the tannins of common beans and rapeseed (canola). 

All nutrients (except water) may undergo either chemical or physical changes during processing that render them inactive or less bioavailable. This occurs for macro- as well as micronutrients. During browning, the amino acid lysine can react with carbohydrates to lower the biological value of protein. 

As with other essentiai nutrients there are homeostatic mechanisms which maintain a constant tissue concentration of zinc in spite of fiuctuations in dietary suppiy. The total dietary intake is 10-15 mg per day. The bioavailability of zinc from different foodstuffs varies. Some 40% of zinc is absorbed from the average diet. Inside the intestinai mucosai ceil zinc enters a metabolic pooi in equiiibrium with zinc-thionein. The synthesis of this metal binding protein is induced by various metals, and it appears to reguiate their intracellular transport. Zinc leaves the intestinal mucosal cell across the plasma membrane and is taken up by albumin in the portal circulation. The liver extracts zinc with a high... 

Despite the fact that a plethora of dietary factors could, and will, affect the absorption characteristics of phytochemicals, this area has not been systematically explored. One reason might be the complexity of dietary factors and their interactions that could affect absorption. A nonexhaustive list would include the volume and composition of the food consumed, pH, caloric density, viscosity, nutrients (carbohydrates, protein, fat, fibers), alcohol, caffeine, and the presence of other phytochemicals. Such dietary factors affect the functional status, motility, and acidity of the gastrointestinal tract in a complex manner and modify the physicochemical properties, formulation, and dissolution characteristics of the compound of interest. Calcium in dairy products, for example, has the potential to chelate tetracyclines and fluoroquinolones and, thereby, reduce their bioavailability and biological activity [31]. 

Phenolic compounds are widely distributed in plant parts from the roots to the seeds and include phenolic acids, flavo-noids and tannins. The tannins may reduce protein digestibility (Ford and Hewitt, 1979) and perhaps the bioavailability of other nutrients. The flavonoids have been reported to have a number of nutritional and pharmacological activities (Kuhnau, 1976). Phenolic acids include benzoic and cinnamic acid derivatives. The benzoic acid derivatives include p-hydroxy-benzoic, protochate-chuic, vanillic, gallic and syringic acids. The cinnamic acids, p-coumaric, caffeic, ferulic and sinapic are found in most oilseeds used to prepare protein concentrates and frequently occur in the form of esters with quinic acid or sugars. Chlorogenic acid for example is an ester of caffeic acid and quinic acid and is found in several isomeric and derivatized forms. 

However, only a fraction of carotenoids absorbed by the human body can effectively contribute to human health, reaches up to 10 % when a natural food is consumed [21]. A number of factors can affect the bioaccessibUity and/or bioavailability, including the species of carotenoids, linkages at molecular level, amount of carotenoid, matrix, effectors, nutrient status, genetics, host-related factors, and interactions among these variables. In carrots, for example, p-carotene is located in the chromoplasts (surrounded by a double bUayer membrane) of the plant cells (surrounded by a cell membrane and a cell wall), where it is often associated with proteins and/or residual membranes. This fact results in several physical barriers that have to be broken to make p-carotene accessible for absorption. 

Problems that may be encountered in the use of special formulas include those based on soy protein and synthetic diets. Trace element deficiencies may result from inadvertently low levels of specific nutrients [15] and/or from poor bioavailability [14]. The practical... 

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