Bleaching Of Solutions Research Articles

Dual-state emission and photochromic properties of spiropyranindoline derivatives bearing an ortho-hydroxyphenylbenzimidazole moiety

Dual-state emission and photochromic properties of spiropyranindoline derivatives bearing an ortho-hydroxyphenylbenzimidazole moiety

Investigation of inclusion complexes of some anthocyanins with hydroxypropyl-β-cyclodextrin

In the present work, a spectrophotometric method (including electronic spectra differences) was applied to investigate complex formations between anthocyanins with hydroxypropyl-β-cyclodextrin (HPbCD). Also the molecular mechanics method (MM+) was used to analyze the system. The possibility of inclusion of complex formations of anthocyanin in flavylium form by incorporating the B ring into “host” cavity is predicted theoretically and is proved experimentally. Complex stability was shown to depend on steric factors in the complexes, defined by the glycoside moiety size at 3 position; due to the change of the closest surrounding geometry of carbon at 2 position (when hybridization of type changes sp2 → sp3), these stresses decrease, which allows the formation of more stable complexes between cyclodextrin and hemiacetal anthocyanin forms accompanied by solution bleaching. The slow anthocyanin forms equilibration is shown to be a property of the systems containing and missing cyclodextrin, and this effect is due to slow equilibration establishment of hemiacetal–chalkone transitions, whose role in inclusion complex formation is negligible.

Influence of external additives on the preservation of carthamin red colour: an introductory test for utilizing carthamin as a herbal colorant of processed foods

A number of carbohydrates and related compounds was admixed with carthamin in an acidic buffer solution and the effect of the test chemicals on carthamin stability examined at low temperature. Monosaccharides were scarcely effective, although slightly accentuated values were obvious in thed-forms (d-form∶l-form=1.3∶1.0). Disaccharides were less effective for carthamin red preservation (dimer∶monomer=1.0∶1.8). However, a high level of colour conservation was observed with sugar alcohols. Both polyethylene glycol and glycerine very effectively protected carthamin from bleaching in solution: the colour preservation rates calculated were 91.3% and 83.8%, respectively, after 24 h incubation at 5° C in the dark. Gelatine was also effective for maintaining carthamin colour (preservation rate: 81.3%). The results are assessed in connection with utilizing carthamin as a herbal colorant of processed foods.