title: Effect of Temperature on Acidity and Hydration Equilibrium Constants of Delphinidin-3-O- and Cyanidin-3-O-sambubioside Calculated from Uni- and Multiwavelength Spectroscopic Data.
abstract: Delphinidin-3-O-sambubioside and cyanidin-3-O-sambubioside are the main anthocyanins of Hibiscus sabdariffa calyces, traditionally used to make a bright red beverage by decoction in water. At natural pH, these anthocyanins are mainly in their flavylium form (red) in equilibrium with the quinonoid base (purple) and the hemiketal (colorless). For the first time, their acidity and hydration equilibrium constants were obtained from a pH-jump method followed by UV-vis spectroscopy as a function of temperature from 4 to 37 °C. Equilibrium constant determination was also performed by multivariate curve resolution (MCR). Acidity and hydration constants of cyanidin-3-O-sambubioside at 25 °C were 4.12 × 10(-5) and 7.74 × 10(-4), respectively, and were significantly higher for delphinidin-3-O-sambubioside (4.95 × 10(-5) and 1.21 × 10(-3), respectively). MCR enabled the obtaining of concentration and spectrum of each form but led to overestimated values for the equilibrium constants. However, both methods showed that formations of the quinonoid base and hemiketal were endothermic reactions. Equilibrium constants of anthocyanins in the hibiscus extract showed comparable values as for the isolated anthocyanins.
authors.affiliation: CIRAD , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Kévin
authors.initials: K
authors.lastname: Vidot
authors.affiliation: Montpellier SupAgro , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Nawel
authors.initials: N
authors.lastname: Achir
authors.affiliation: CIRAD , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Mertz
authors.affiliation: CIRAD , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: André
authors.initials: A
authors.lastname: Sinela
authors.affiliation: CIRAD , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Nadirah
authors.initials: N
authors.lastname: Rawat
authors.affiliation: CIRAD , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Alexia
authors.initials: A
authors.lastname: Prades
authors.affiliation: UMR 408, University of Avignon, INRA , Safety and Quality of Plant Products, 84000 Avignon, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Dangles
authors.affiliation: INRA-IPV , Unité de Recherche des Polymères et des Techniques Physicochimiques, 2 place Viala, 34060 Montpellier, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Fulcrand
authors.affiliation: Montpellier SupAgro , UMR 95 Qualisud, TA B-95/16, F-34398 Montpellier Cedex 5, France.
authors.forename: Manuel
authors.initials: M
authors.lastname: Dornier
mesh_terms: D000872:Anthocyanins / Q000737:chemistry*; D004187:Disaccharides; D035264:Flowers / Q000737:chemistry; D031584:Hibiscus / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010936:Plant Extracts / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D000872:Anthocyanins; D004187:Disaccharides; D010936:Plant Extracts; C505011:delphinidin 3-sambubioside; C546691:cyanidin 3-sambubioside
keywords: Hibiscus sabdariffa extract; MCR; UV−vis; anthocyanin; cyanidin-3-O-sambubioside; delphinidin-3-O-sambubioside; equilibrium constant; pH-jump