Effect of external conditions on the stability of enzymically synthesized carthamin

Abstract

Enzymically synthesized carthamin was subjected to testing of its stability under various conditions. It easily turned to unknown reddish-yellow or orange-yellow substances in water. This instability was further accelerated by the presence of a sulfhydryl reagent and or at higher temperature. In a typical result, the rate of the discolouration was calculated to be 21 nmol carthamin h^-1 at 20 °C in water and rose to 44.0 nmol carthamin h^-1 at 60 °C in water containing 1.0 mM 2-mercaptoethanol. Organic solvents such as methanol, ethanol and acetone showed little effect on carthamin discolouration, while the stability of carthamin in these solvents was gradually decreased by rising temperature. In various buffers, in the acidic range. carthamin was relatively stable, whereas, it turned unstable on the basic side. All of the thiol reagents tested were unfavourable for retaining stability of carthamin in solutions. 2-Mercaptoethanol, reduced glutathione and thioglycollic acid exhibited the strongest degrading effect on the pigment. At the 1.0 mM level, 2-mercaptoethanol reduced the absorption peak at 517 nm by 0.02 min^-1, which corresponded to 0.12 nmol carthamin cm^-3 min^-1 L-Methionine, L-ascorbic and D-araboascorbic acids were found to be strong bathochromic effectors For example, L-methionine rised AA 517 nm up to 0.01 min^-1, whose value equaled to 0-1 nmol carthamin cm^-3 min^-1 at 30 °C Carthamin was absorbed and adsorbed and stabilized by many macro-molecular Substances. Among the compounds tested, cellulose was found to be the most effective stabilizer. The stabilization effect of cellulose was specific for carthamin and the term "SAITO EFFECT" is proposed for it. This effect was reduced by hydrolysis of the carthamin-adsorbed cellulose with Asperqillus cellulase in an incubation system