Browning systems

Ferretti, A. and Flanagan, V. P. 1971. The lactose-casein (Maillard browning-system. Volatile components. J. Agri. Food Chem. 19, 245-249. 

Nitrite Interactions in Model Maillard Browning Systems... 

Amadori compounds (N-substituted-l-amino-l-deoxy-2-ketoses) are potential precursors to the formation of many of these heterocyclic volatile products. The secondary nitrogen in most Amadori compounds is weakly basic and is therefore a likely site for rapid nitrosation reactions via normal reactions with nitrous acid, under mildly acidic conditions. However, purified Amadori compounds are usually obtained only after tedious isolation procedures are invoked to separate them from the complex mixtures of typical Maillard browning systems. Takeoka et al. ( 5) reported high performance liquid chromatographic (HPLC) procedures to separate Amadori compounds in highly purified form on a wide variety of columns, both of hydrophilic and hydrophobic nature. They were able to thus demonstrate that reaction products could be followed for kinetic measurements as well as to ensure purity of isolated products. 

Thus, by the Maillard reaction in different browning systems of sugars and amino compounds, some mutagenic substances were formed, although their activities are quite weak compared with those formed by pyrolysis of amino acids. They were confirmed as intermediates and some of them were identified as furan, pyrrole, or thiazolidine derivatives formed from glucose and amino acids... 

A. V. Clark and S. R. Tannenbaum, Isolation and characterization of pigments from protein-carbonyl browning systems Isolation, purification, and properties, J. Agric. Food Chem., 1970, 18, 891-894. 

Methylpyrrole is one of the four pyrroles isolated in the pyrolysis of trigonelline by Viani and Horman (1974). It was also formed by heating D-xylose with methylamine (Kato, 1966), from a cysteine/ cystine ribose browning system (Mulders, 1973c). Kato and Fujimaki (1968) observed the formation of A -substituted pyrrole-2-carbaldehydes when D-xylose reacted thermally with various amines or amino acids (glycine, alanine, 3-alanine, leucine). The intermediate 3,4-dideoxypentosulos-3-ene would either give 2-furaldehyde (mainly with a-amino acids) or substituted pyrrole-2-carbaldehydes and melanoidins (with 3-alanine or other amines). 

Ferretti and Flanagan (1971a) found it in a lactose/casein browning system, Shibamoto et al. (1979) in a i>glucose/ammonia model system, Baltes and Bochmann (1987b) in serine/threonine/sucrose systems (and in coffee). 

Mulders (1973c) identified 1-furfurylpyrrole in a cysteine/cystine ribose browning system, Shibamoto et al. (1979) in a D-glucose/ammonia model system, Ho and Chen (1999) in a Maillard reaction of threonine with ribose as a main volatile product, Baltes and Bochmann (1987b) when heating serine and/ or threonine with sucrose (and in coffee). According to Tressl et al. (1981c), this compound was also formed from 4-hydroxyproline and 2-furaldehyde. 

Ferretti A. and Flanagan V.P. (1973) Characterization of volatile constituents of an V-alpha-formyl-i-lysinc-D-lactose browning system. J. Agric. Food Chem. 21, 35-7. 

Figure 4 shows experimental and predicted phase equilibria for the acetonitrile/benzene system at 45°C. This system exhibits moderate positive deviations from Raoult s law. The high-quality data of Brown and Smith (1955) are very well represented by the UNIQUAC equation. 

Table 1 indicates that the enthalpy of mixing in the liquid phase is not important when calculating enthalpies of vaporization, even though for this system, the enthalpy of mixing is large (Brown, 1964) when compared to other enthalpies of mixing for typical mixtures of nonelectrolytes. 

In employing this method, an important precaution to take is to use a tip that has been ground smooth at the end and is free tom any nicks. In the case of liquids that do not wet the tip, r is the inside radius. Volatile liquids are studied in a closed system as described by Harkins and Brown [21] to minimize evaporation losses. 

Zumbusch A, Fleury L, Brown R, Bernard J and Orrit M 1993 Probing individual two-level systems in a polymer by correlation of single molecule fluorescence Phys. Rev. Lett. 70 3584-7... 

Still another possibiUty is a marine biomass plantation such as that envisaged for giant brown kelp grown off the California coast and conversion of the kelp to methane in a system similar to that shown in Figure 19. The location of the SNG plant could be either on a floating platform near the kelp growth area or located on shore, in which case the biomass or fuel transport requirements would be different. 

B. A. Sykes and D. Brown, A Review of the Technology of High Pressure Systems, Institute of Gas Engineers, London, 1975. 

Because of the wide variation in composition and properties of brown coal (see Table 3), efficient combustion of these fuels caimot be accomphshed by a single system. The moisture content limits combustion efficiency because some chemical energy is required to convert Hquid water to steam in the flue gases. The steam then increases the dew point of the gases, requiring higher temperatures to avoid condensation in the stack. For fuels up to 25% moisture content, 80% efficiency can be achieved. As the moisture content increases to 60%, the efficiency decreases to 70% and efficiency continues to decline about another 1% for each additional 1% moisture to 70%. 

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