Amino acids rendering products

Browning caused by Maillard-type reactions between carbohydrates and amino acids or caramelisation contribute to appearance, taste and flavour of many products. Carbohydrate sweeteners are important for these reactions, and other types of sweetening agents may not react in a similar way, therefore rendering products more pale. 

Numerous amino acids—including diamino- and oxyamino-acids— have also been synthesised of recent years by Neuberg and his coworkers and by Sorensen. Our knowledge of these acids should render the task of identifying a new unit in the protein molecule less laborious than it has hitherto been. Their preparation was no doubt due to the possibility of the presence of other units than those above described, which possibility will not be excluded until the quantity of products isolated reaches lOO per cent. 

These transformations are efficient under biological conditions only if another activating group is present (carbonyl, aryl, etc.) [77]. Such an activating group is important to render the elimination product (resulting from the loss of a fluoride ion) a better Michael acceptor. Moreover, if one or several fluorine atoms are present on the double bond, the latter is also more reactive (Fig. 22). Thus, the elimination, promoted by the enzyme, of a fluoride ion from a jS-fluoro amino acid leads to a very reactive Michael acceptor. The latter can undergo an irreversible addition of a nucleophile residue of the active site of the enzyme, which is thus inhibited (Fig. 23) [78,79]. 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

There are many chemical procedures used for rendering the spots on the plate visible some procedures are general and they expose all the components in the mixture as visible derivatives, whereas others are very specific, and only provide colored derivatives with selected chemical types, e.g. amino acids. Examples of both classes of derivatization will be given but, irrespective of the type of product that is chosen, some pre-treatment will be necessary. After chromatographic development, the plate will be wet with the mobile... 

Rendered animal proteins are especially valuable to the livestock and feed industry because of their high protein content, digestible amino acid levels (especially lysine), mineral availability (especially calcium and phosphorous), and relatively low cost in relation to their nutrient value. They have few close substitutes in most rations, although specific feeding characteristics of animal products can be... 

Using this method, the preparation of 1 could be accomplished starting from a protected (R)-4-fluorophenylalanine 2 (Fig. 3). Upon deprotection and diazotiza-tion, the desired product could be obtained in a modest yield of 50% for two steps via the isolated intermediate 3. However, the starting amino acid 2 is fairly expensive and the optical purity of the product 1 varied from a low 78% to a high 97% in scaled-up runs, indicating that the process is not robust. Both problems render this method impractical for production at a large scale. 

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