Colour activity value

Fogliano et al.72 have prepared melanoidin [molecular mass (MM) >12 kDa] from glucose-glycine, lactose-lysine, and lactose-iV-acetyllysine lactose-lysine proved to be the odd one out, exhibiting less than one-tenth the absorbance of the other two at 460 and 520 nm. Their CAVs (colour activity value,73 defined as the ratio of a colorant s concentration to its visual detection threshold, both in pg kg-1) were 8000, 200, and 4000, respectively. Examination by MALDI-TOF gave results only for the lactose-A-acetyllysine melanoidin, with peaks around 6,12, and 24 kDa (the spectrum reproduced by Borrelli et al.74 shows peaks around 6, 7.5, and 12 kDa). The antioxidant effects of the melanoidins were also examined (see p. 129). 

In many ways, colour, which is a sensation, should be assessed visually. On analogy with the treatment of odorants, Hofmann73 has taken a crucial step in this area by defining a colour dilution factor (CD) and a colour activity value (CAV). CD is the factor required for any solution of a colorant x to be diluted to its colour threshold. CAVX is the ratio of the concentration of x (jug kg-1) to its threshold concentration (jug kg-1)- The colour contribution of a component colorant to the colour of a mixture can then be defined as... 

To verify whether the volatiles listed in Table 6.32 are actually the key odorants, an aroma model was prepared by using an unripened cheese (UC) as base ]53J. The odorants and in addition the compoimds showing high taste activity values ]54] were quantified in UC and in Swiss cheese ]53]. The differences in the concentration of these compounds in both samples were calculated, and, accordingly, the compounds were dissolved in water and/or sunflower oil and then added to freeze-dried UC. The flavour model obtained agreed in colour, pH, water, protein and fat content with grated Swiss cheese, only the texture was more grainy ]53]. 

Pharmacopoeial methods rely heavily on simple analysis by UV/visible spectrophotometry to determine active ingredients in formulations. These methods are usually based on the use of a standard A (1 %, 1 cm) value for the active ingredient being assayed and this relies on the UV spectrophotometer being accurately calibrated as described earlier in the chapter. Such methods also presume that there is no interference from excipients (preservatives, colourants, etc.) present in formulations and that the sample is free of suspended matter, which would cause light scattering. 

Figure 9.1. When a mutation in an individual produces a new enzymic activity, capable of producing a novel substance from an existing substrate, selection pressures will act on that individual which will be related to the cost of production of the new substance and the value of that substance to the producer. The novel substance will bring intrinsic properties to the producer, properties such as the possession of biomolecular activity or useful physicochemical properties such as colour. However, if the novel substance is converted by other existing enzymes to yet more novel chemicals, the inherent properties of those other novel substances will have been derived from the properties of the original novel substance.

Experimental measurements of absorption fluxes and colour development for the gas-liquid reaction between sulphur trioxide and dodecylbenzene have been carried out in a stirred cell absorber. A model with two parallel reaction paths representing sulphonation and discolouration has been applied to analyse the exothermic absorption accompanying conversions up to 70%. The results show that the two reactions have similar activation energies and that temperature increases greater than 100°C occur at the interface during absorption. The absorption enhancement factor exhibits a maximum value as liquid phase conversion proceeds. 

Towards organic substances ozone is strikingly active. Organic colouring matters are bleached for example, indigo is oxidised to isatin.8 Turpentine rapidly absorbs the gas, and if the hquid is exposed on filter paper in an atmosphere of ozone, inflammation may occur.9 India-rubber is rapidly attacked and so is of little value for connections... 

The application of an electric field above the threshold value results in a reorientation of the nematic liquid crystal mixture, if the nematic phase is of negative dielectric anisotropy. The optically active dopant then applies a torque to the nematic phase and causes a helical structure to be formed in the plane of the display. The guest dye molecules are also reoriented and, therefore, the display appears coloured in the activated pixels. Thus, a positive contrast display is produced of coloured information against a white background. The threshold voltage is dependent upon the elastic constants, the magnitude of the dielectric anisotropy, and the ratio of the cell gap to the chiral nematic pitch ... 

Figure 6.6 Graphics involved in the interpretation of GRIND-based 3D QSAR models. Variables with the highest and lowest PLS coefficients were investigated, first in a plot representing the correlograms obtained for all the compounds in the series where the colour represents the value of the yvariable (red for active compounds and blue for inactive). Then, these variables were represented in 3D for highly active and inactive compounds, in order to identify the structural and physicochemical features they represent.

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