Effects of reaction mixture and other components on the determination of the equilibrium and rate constants of the hydration reactions of anthocyanins

Abstract The equilibrium and rate constants of the hydration and deprotonation reactions of anthocyanins show how their color intensity changes with pH. In the cases of several anthocyanins, the constants for each obtained by several methods are different. In an effort to resolve these discrepancies, we have examined the effects of several components of the pH-jump experiments on the values of the constants. Storage of the buffers to be used in pH-jump experiments in Pyrex or borosilicate glass bottles results in increasing Al3+ concentration in the buffers over several weeks. When these buffers are used, the anthocyanins with two OH groups on the B ring complex with the Al3+ which leads to major changes in their spectra, in the equilibrium position, and in the apparent first-order rate constant. Thus, constants determined on the same anthocyanin using the same buffers stored in glass bottles may be different at different times. During the reduction of the experimental data to the rate and equilibrium constants, two divergences from the expected behavior were found. In the calculation Ka + Kh for the anthocyanin acylated with 4-hydroxy-3,5-dimethoxycinnamic acid (6-O-(4-hydroxy-3,5-dimethoxycinnamoyl)-β- d -glucopyranosyl-(1 → 6)-[β- d -xylopyranosyl-(1 → 2)]-β- d -galactopyranosyl-(1 → O3)-cyanidin), the plotted points appear to fit two straight lines, intersecting at an equilibrium pH near pH 4. In the calculation which leads to the individual constants of both anthocyanins examined here, the points below an equilibrium pH of pH 4 curve upward from the line that describes the points from an equilibrium pH above 4. Differences in the composition of solutions used in pH-jump experiments examined here, include (1) the addition of phosphate to the acetate buffer, (2) the presence of 0.5 M NaCl, and (3) the solution of the anthocyanin in either 0.1 N HCl or 0.1 N HOAc. These changes gave differences that were statistically significant in some of the constants for each of the two anthocyanins examined. The constants were both qualitatively and quantitatively different.

[1]  J B Harborne,et al.  Anthocyanins and other flavonoids. , 2001, Natural product reports.

[2]  Antonio M. Martin,et al.  An overview of pigment production in biological systems: Functions, biosynthesis, and applications in food industry , 1994 .

[3]  R. Brouillard,et al.  Anthocyanin–aluminium and –gallium complexes in aqueous solution , 1997 .

[4]  Norio Saito,et al.  Kinetic and thermodynamic control of flavylium hydration in the pelargonidin-cinnamic acid complexation. Origin of the extraordinary flower color diversity of Pharbitis nil , 1993 .

[5]  R. E. White,et al.  The existence of polymeric complexes in dilute solutions of aluminium and orthophosphate , 1976, Plant and Soil.

[6]  P. Markakis,et al.  Food colorants: anthocyanins. , 1989, Critical reviews in food science and nutrition.

[7]  D. Baker,et al.  Rate and equilibrium constants for the dehydration and deprotonation reactions of some monoacylated and glycosylated cyanidin derivatives. , 1999, Journal of agricultural and food chemistry.

[8]  P. Markakis.  Anthocyanins as Food Colors , 1982 .

[9]  M. J. Ahmed,et al.  Spectrophotometric determination of aluminium by morin. , 1995, Talanta.

[10]  N. Saitǒ,et al.  Recent Progress in the Chemistry of Polyacylated Anthocyanins as Flower Color Pigments , 2002 .

[11]  R. Brouillard,et al.  Anthocyanin Intramolecular Interactions. A New Mathematical Approach To Account for the Remarkable Colorant Properties of the Pigments Extracted from Matthiola incana , 1996 .

[12]  T. Goto,et al.  Unusually stable monoacylated anthocyanin from purple Yam Dioscorea alata , 1991 .

[13]  R. Brouillard,et al.  New aspects of anthocyanin complexation. Intramolecular copigmentation as a means for colour loss? , 1996, Phytochemistry.

[14]  T. Goto,et al.  Structure and Molecular Stacking of Anthocyanins—Flower Color Variation , 1991 .

[15]  R. Carle,et al.  Color and antioxidant properties of cyanidin-based anthocyanin pigments. , 2002, Journal of agricultural and food chemistry.

[16]  H. Seitz,et al.  Effects of supplied cinnamic acids and biosynthetic intermediates on the anthocyanins accumulated by wild carrot suspension cultures , 1994, Plant Cell, Tissue and Organ Culture.

[17]  K. R. Markham.  Techniques of flavonoid identification. , 1982 .

[18]  J. W. Akitt,et al.  Nuclear magnetic resonance and Raman studies of the aluminium complexes formed in aqueous solutions of aluminium salts containing phosphoric acid and fluoride ions , 1971 .

[19]  J. Salmon,et al.  221. Aluminium phosphates. Part II. Ion-exchange and pH-titration studies of aluminium phosphate complexes in solution , 1958 .

[20]  Elena G. Gakh,et al.  ANTHOCYANINS FROM WILD CARROT SUSPENSION CULTURES ACYLATED WITH SUPPLIED CARBOXYLIC ACIDS , 1998 .

[21]  R. Brouillard,et al.  Kinetic and thermodynamic investigation of the aluminium–anthocyanin complexation in aqueous solution , 1994 .

[22]  Montserrat Filella,et al.  Aluminum speciation studies in biological fluids. Part 3. Quantitative investigation of aluminum-phosphate complexes and assessment of their potential significance in vivo. , 1990, Journal of inorganic biochemistry.