Amino acids in milk

Storage proteins serve as a which are proteins that fight infections, source of amino acids in milk. 

Rassin, D. K. Sturman, J. A. and Gaull, G. E. 1978. Taurine and other free amino acids in milk of man and other mammals. Early Human Dev. 2, 1-13. 

Aboshana, K. and Hansen, A. P. 1977. Effect of ultra-high-temperature steam injection processing on sulfur-containing amino acids in milk. J. Dairy Set 60, 1374-1378. 

Light-induced oxidation of proteins has been shown to lead to off-flavors and destruction of essential amino acids in milk. Patton (1954) demonstrated that sunlight attacks methionine and converts it into methional (( -methylmercaptopropionaldehyde), which can cause a typical sunlight off-flavor at a level of 0.1 ppm. It was later demonstrated by Finley and Shipe (1971) that the source of the light-induced off-flavor in milk resides in a low-density lipoprotein fraction. 

Amino acids in milk have been separated by Bujard and Mauron [17] on a cellulose MN-300 layer. According to Keller and Pataki [91], 24 amino acids can be detected in sperm fluid. Since human ejaculate contains several proteolytic enzymes, the authors have drawn conclusions about the individual proteolytic activities from this result. Mouhg-RABI [109a] reports the separation of amino acids from the perilymph of the inner ear, using ion exchange TLC with gradient elution. 

Gandolfi 1, Palla G, Delprato L et al (1992) o-Amino acids in milk as related to heat-treatments and bacterial-activity. J Food Sci 57 377-379... 

Stoll, B., J. Henry, P.J. Reeds, H. Yu, E. Jahoor and D.G. Burrin, 1998. Catabolism dominates the first-pass intestinal metabolism of dietary essential amino acids in milk-replacer fed piglets J. Nutr. 128, 606-614. 

Lysine is an essential amino acid that is mainly provided by meat products and is therefore limited in diets where wheat is the primary protein source. Lysine is also the first rate-limiting amino acid in milk-fed newborns for growth and protein synthesis. Lysine is catabolized to glutamate and acetyl-CoA and is also the precursor for the synthesis of carnitine, which is needed for mitochondrial oxidation of long-chain fatty acids. 

The enzymatic hydrolysates of milk casein and soy protein sometimes have a strong bitter taste. The bitter taste is frequently developed by pepsin [9001 -75-6] chymotrypsin [9004-07-3] and some neutral proteases and accounted for by the existence of peptides that have a hydrophobic amino acid in the carboxyhc terminal (226). The relation between bitter taste and amino acid constitution has been discussed (227). 

There have also been reports [36, 37] that racemization of amino acids occurs more rapidly using MW heating than conventional heating at the same temperature. Chen et al. [36] observed that racemization of amino acids in acetic acid the presence of benzaldehyde was accelerated by MW heating. Lubec et al. [37] reported that some D-proline and ris-4-hydroxy-D-proline were found in samples of infant milk formula when they were heated in a MW oven. On the other hand, conventionally heated samples did not contain these unnatural D-amino acids. This report caused concern, and received media attention because D-proline is neurotoxic and suggested that MW heating of some foods could have deleterious effects on their nutritional value and the health of the consumer. 

What is most remarkable is that cells can produce proteins with strikingly different properties and activities by joining the same 20 amino acids in many different combinations and sequences. From these building blocks different organisms can make such widely diverse products as enzymes, hormones, antibodies, transporters, muscle fibers, the lens protein of the eye, feathers, spider webs, rhinoceros horn, milk proteins, antibiotics, mushroom poisons, and myriad other substances having distinct biological activities (Fig. 3-1). Among these protein products, the enzymes are the most varied and specialized. Virtually all cellular reactions are catalyzed by enzymes. 

Proteins from animal sources Proteins from animal sources (meat, poultry, milk, fish) have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins (Figure 27.18). [Note Gelatin prepared from animal collagen is an exception it has a low biologic value as a result of deficiencies in several essential amino acids.]... 

H Brueckner, P Jaek, M Langer, H Godel. Liquid chromatographic determination of D-amino acids in cheese and cow milk. Implication of starter cultures, amino acid racemases, and rumen microorganisms on formation, and nutritional considerations. Amino Acids 2 271-284, 1992. 

Quantities of amino acids in nonprotein fraction of breast and cow s milk. Arch. Biochem., 25, 350 (1950). With D. Bolling. 

There are two pyridoxal phosphate-requiring enzymes in the homocysteine degradation pathway, which are associated with genetic diseases. In homo-cystinuria, cystathionine synthase is defective, and large amounts of homocystine are excreted in the urine. Some homocystinurics respond to the administration of large doses of vitamin B6. In cystathioninuria, cystathionase is either defective or absent. These patients excrete cystathionine in the urine. Cystathionase is often underactive in the newborns with immature livers, and cysteine and cystine become essential amino acids. Human milk protein is especially rich in cysteine, presumably to prepare the newborn for such a contingency. 

Proteins that provide all the essential amino acids in about the right proportions for human nutrition are called complete proteins. Examples of complete proteins are those in meat, fish, milk, and eggs. About 50 g of complete protein per day is adequate for adult humans. 

The reaction velocity and pattern are influenced by the nature of the reacting amino acid or protein and the carbohydrate. This means that each kind of food may show a different browning pattern. Generally, lysine is the most reactive amino acid because of the free e-amino group. Since lysine is the limiting essential amino acid in many food proteins, its destruction can substantially reduce the nutritional value of the protein. Foods that are rich in reducing sugars are very reactive, and this explains why lysine in milk is destroyed more easily than in other... 

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