Buffer model system

Ryu, D. et al., Heat stability of zearalenone in an aqueous buffered model system, J. Agric. Food Chem., 51, 746, 2003. 

A response surface model of the effects of HA protein concentration (gliadin, the wheat prolamin), HA polyphenol concentration (tannic acid, TA), alcohol, and pH on the amount of haze formed was constructed using a buffer model system (Siebert et al., 1996a). Figure 2.12 shows the effects of protein and polyphenol on haze predicted by the model at fixed levels of pH and alcohol. The model indicates that as protein increases at fixed polyphenol levels, the haze rises to a point and then starts to decline. Similarly, when polyphenol increases at a fixed protein level, the haze increases to a maximum and then declines. 

Previous studies which have shown an effect of pH on aroma volatiles have been carried out in model systems with pH controlled by the addition of phosphate buffers or in the absence of buffer. The present work has demonstrated that in a food system with strong buffering capacity (meat) the formation of furan thiols and sulfides is strongly influenced by pH, thus confirming the earlier work in buffered model systems. 

The salt (buffer) type and concentration may also influence reaction rate. While buffers vary in their effect on the Maillard reaction, it is generally accepted that phosphate is the best catalyst [27], The effect of phosphate on reaction rate is pH dependent with it having the greatest catalytic effect at pHs between 5-7. Potman and van Wijk [27] found the Maillard reaction rate in a phosphate buffered model system increased from 10- to 15-fold compared to a phosphate free reaction system. 

Compound (Miles Laboratories, Elkhart, IN), snap-frozen, and cut into sections for comparison with paraffin-embedded cell sections (3) FFPE Cell Blocks Six cell pellets were fixed in 10% neutral buffered formalin immediately after harvest, at room temperature for 6,12,24h, 3,7, and 30 days, respectively. For further comparison with the cell model system, recently collected sample of human breast cancer tissues were processed by OCT-embedding and snap-freezing the corresponding routine FFPE block that was obtained from the Norris Cancer Hospital and Research Institute at the University of Southern California Keck School of Medicine (USC). This tissue block was processed routinely (formalin-fixed 24h and processed by automatic equipment). 

Electroless Ni-Ge-P was studied as a model system for ternary alloy deposition [112], A chloride-free solution with GeC>2 as a source of Ge, hypophosphite as reducing agent, aspartic acid as a selective complexant for Ni2+ ions, which was operated at 80 °C in the pH range of 5-5.8, was developed for depositing Ni-Ge-P films with a tunable Ge content from 0 to 25+ at%. The use of a complexant such as citric acid, which complexed Ge(IY) ions as well as Ni2+ ions, resulted in a much lower Ge content in the electroless deposit, and a more complicated solution to study for the reasons discussed above. The aspartate-containing electroless solution, with its non-complexing pH buffer (succinic acid), approximated a modular system, and, with the exception of the aspartic acid - Ni2+ complexation reaction, exhibited a minimum level of interactions in solution. 

In this connection, the use of insoluble agents as photosensitizers seems promising. This approach, in particular, has been realized in respect to the suspension of crystal fullerene C60 (Kasermann and Kempf, 1997, 1998). Its marked advantage is that there are no byproducts of the destruction of fullerene and the compound can be easily removed from the solution by centrifugation. The high efficiency of C60 in viral inactivation has been demonstrated for specific enveloped viruses such as Semliki forest vims (SFV) and vesicular stomatitis vims (VSV) (Kasermann and Kempf, 1997, 1998). The inactivation was achieved in a model system where the vims was suspended in a saline buffer solution. The addition of 2% bovine serum albumin did not affect the kinetics of the photoinactivation of the vims. 

Kuo, R.J. Matijevic, E. (1980) Particle adhesion and removal in model systems. III. Monodisperse ferric oxide on steel. J. Colloid Interface Sci. 78 407-421 Kuo, S. Jellum, E.J. (1994) The effect of soil phosphorus buffering capacity on phosphorus extraction by iron oxide-coated paper strips in some acid soils. Soil Sci. 158 124-131... 

Using stoichiometric model systems, it can be shown that some naturally occurring redox processes have a pronounced pH-controlling action, even in the presence of substances that act as buffers. High pH values can be reached particularly in systems where higher metal oxides act as oxidizers whereas an acid condition often develops when free oxygen is the oxidizer. However, in most natural systems carbonates and silicates have a more pronounced pH controlling effect than redox processes. 

A model system demonstrating the nutritional destruction of lysine in bovine plasma albumin (BPA) by reaction with either a dialdehyde (MA) or a keto-aldehyde (MGA) was studied in relation to reaction rates as affected by pH, temperature, reaction time and carbonyl concentration. The BPA was Fraction V obtained from Schwartz/Mann and had a molecular weight of 69 x 103 with sixty lysine residules/mole, an assayed content of 11.4%. It was dissolved in 0.0200 M phosphate-citrate buffer adjusted to the desired pH. Malonaldehyde was prepared by acid hydrolysis of its bis-(dimethyl acetal). An aqueous solution of pyruvic aldehyde was diluted with distilled water and phosphate-citrate buffer to give an MGA solution of the desired pH (16). 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

In initial work, L- a-phosphatidylcholine (lecithin) from egg yolk was selected as the phospholipid, and later studies compared other phospholipids and lipid extracts from meat. As the study originated from investigations of cooked meat flavor, the model system reactions were carried out in aqueous solution buffered with phosphate at an initial pH of 5.7 and concentrations of the reactants were selected to approximate their relative compositions in mammalian muscle. The reactions were carried out under pressure... 

Sulfite can be used as an inhibitor to trap intermediates in model systems.175 Its use (0.2 M) has been explored with mixtures of 6-aminohexanoic acid (0.38 M) and xylose or glucose (2.8 M) in phosphate buffer, (pH 7.35) at 37 °C. Ion-exchange chromatography and HPLC allowed yellow compounds 21 and 22 to be isolated, respectively. They exist in equilibrium with their hemiacetals. 

A basic group of the enzyme catalyzes the proton transfer characteristics of transaminations. Bruice found that imidazole buffer can catalyze transamination reactions in model systems [6], We conjectured that transamination rates should be improved by attaching a basic side arm to pyridoxamine. Thus we synthesized a series of simple pyridoxamine derivatives carrying basic groups at the end of flexible chains of various lengths [7-9]. We measured the transamination rates of these pyridoxamine derivatives in the presence of Zn(OAc)2 at pH 4.00 in methanol. 

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