Amino acids with sugar

A common thread that can link the ammonium and peptone catalyst poisoning results just described could be the Maillard reactions of amino acids with sugars (5). Recent studies have shown that the ammonium ion is highly reactive, more so than substituted versions (6). Its use as ammonium bicarbonate in developing flavoring compounds by Maillard reactions in extrusion cookers has been reported (7). It is likely that such reactions could occur at our processing conditions. We can speculate that such products could have acted as catalyst surface poisons, which might have been subsequently washed from the catalyst, before it was reused in its active form. 

The aroma precursors have been selected by taking into account the significant role of the Maillard reaction. Indeed, most aroma compounds of this type are formed by the reaction of amino acids with sugars or their degradation products. So we have obtained roast beef, roast mutton and heated vegetable aromas after having treated a mixture of amino acids and glucose at different temperatures and for varied times. 

Cysteine is an important precursor of meat flavor and is therefore often being used in precursor systems for the industrial production of meat process flavorings (1-4). Meat flavor development in these systems is usually based on the Maillard reaction of cysteine (and other amino acids) with sugars. Unfortunately, there are a few complications that prevent that high yields of volatile flavor compounds are obtained from these reactions. The first... 

The reaction of amino acids with sugars to form Schiff s base-type compounds has been often suggested to be a feasible process in the formation of coloured condensed material in seawater, particular in the presence of clay minerals (Hedges, 1978). It is also worthy to note that natural free sugars and amino acids when heated in seawater form fluorescent compounds whose excitation and emission maxima correspond with those formed on reaction of amines with aldehydes (Honda et al., 1974). These experiments were performed at high temperatures (G. Liebezeit, R. Dawson and K. Mopper, unpublished results) and there is some suggestion that the apparent disappearance of amino acids on standing in seawater at room temperature, may be connected in part to this abiotic process. 

Table 1. Aroma generated by the heating of amino acid with sugars ...

The gradients of H, Na, and other cations and anions established by ATPases and other energy sources can be used for secondary active transport of various substrates. The best-understood systems use Na or gradients to transport amino acids and sugars in certain cells. Many of these systems operate as symports, with the ion and the transported amino acid or sugar moving in the same direction (that is, into the cell). In antiport processes, the ion and the other transported species move in opposite directions. (For example, the anion transporter of erythrocytes is an antiport.) Proton symport proteins are used by E. coU and other bacteria to accumulate lactose, arabinose, ribose, and a variety of amino acids. E. coli also possesses Na -symport systems for melibiose as well as for glutamate and other amino acids. 

Heikkila H. (1983) Separating Sugars and Amino Acids with Chromatography, Chem. Eng., January 24, 50-52. 

Studies on the bitterness of other compoundsdo not, however, support this model. The bitter amino acids and sugars, for example, do not possess an AH,B unit of this dimension. As already mentioned, there is some evidence suggesting that there is more than one type of bitter-taste quality and receptor. If this is the case the diterpenes probably interact with a receptor showing a steric requirement difierent from that involved with the other classes of compounds. 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

Figure 2. Scheme for formation of nitrogenous polymers In soils by condensation of amino acids with polyphenols and sugars. 

When passage of a sugar solution at 90°C through a weak-base anion exchange resin was interrupted, an explosion occurred. This was attributed to an exothermic Maillard reaction (interaction of an amino acid with a glycosidic OH group) under the poor heat transfer conditions in a particulate bed without fluid flow. 

The collection of a reference material for trace metals could complement collection of samples for other priority analytes including DOM and DOC. Seawater used for DOM analysis can also be collected in Teflon , for example. Although samples for DOM are not normally stored in plastic bottles (as the iron reference material would be), releases of plasticizers are minimal and are not expected to interfere with the detection of individual organic compounds such as amino acids and sugars. 

Ozone causes both quantitative and qualitative changes in carbon dioxide fixation patterns. Wilkinson and Bames, using carbon dioxide-found a reduction in radioactivity in soluble sugars and increases in free amino acids and sugar phosphates in white pine after a 10-min exposure to ozone at 0.10 ppm. Miller observed a decrease in carbon dioxide-fixation in ponderosa pines that correlated with loss of chlorophyll, after exposure to ozone at 0.30-0.35 ppm. The Hill reaction rates of chloroplasts isolated from healthy and ozone-injured ponderosa pine indicated that both light and dark reactions of the chloroplasts from ozone-injured plants were depressed. Barnes found depressed photosynthesis and stimulated respiration in seedlings of four pine species of the southeastern United States after exposure to ozone at 0.15 ppm. 

The concept of d and l as configurational descriptors is well established, particularly in amino acids and sugars frankly, however, we could live without them and save ourselves a lot of confusion. Since they are so widely used, we need to find out what they mean, but in most cases the information conveyed is less valuable than sticking with R and S. 

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