Thermal degradation of anthocyanins with particular reference to the 3‐glycosides of cyanidin. I. In acidified aqueous solution at 100 °C

Abstract

Several highly purified 3-glycosides of cyanidin were degraded at 100 "C in weak aqueous hydrochloric acid at various pH values between 1 and 4 under both nitrogen and oxygen atmospheres and it was shown that the aglyconesugar bond is the most labile of the glycosidic bonds at pH 2 to 4. At pH 1 .O, however, all the glycosidic bonds are susceptible to hydrolysis.Evidence is presented that phenolic aglycones, and glycosides of undetermined structure, are formed during anthocyanin degradation. An essentially colourless phenolic product, tentatively identified as the chalcone or a-diketone of cyanidin, was observed during the breakdown of all the cyanidin-3-glycosides studied in the pH range 1 to 4. This compound is stable under anaerobic conditions but easily degraded in atmospheres of oxygen.The rate of sugar formation was found to be similar to the rate of red colour loss and to the rate of anthocyanin disappearance in the pH range 2 to 4 showing that glycosidic hydrolysis and not opening of the pyrylium ring is the rate-determining step of the principal reaction leading to red colour loss. At pH 1 .O (anaerobic conditions), the rate of red colour loss lags behind the rate of anthocyanin degradation because the red, cationic form of cyanidin is fairly stable at this low pH. Complete hydrolysis of the anthocyanin takes place at pH 1.0 in contrast to the partial hydrolysis observed in the pH range 2 to 4.The qualitative and, quantitative information reported in this paper led to the proposal of a mechanism for anthocyanin degradation and the red colour loss which accompanies it for the pH range 2 to 4.

Chemical stability of açai fruit (Euterpe oleracea Mart.) anthocyanins as influenced by naturally occurring and externally added polyphenolic cofactors in model systems

“…Applied to these fruit models, a gradual hydrolysis of glycosidic bonds would lead to increased cyanidin-3-glucoside and decreased cyanidin-3-rutinoside concentrations during storage of açai fruit anthocyanins and result in higher proportions of the more labile cyanidin-3-glucoside subsequently a more rapid rate of anthocyanin and colour degradation. Moreover, hydrolysis of the glycosidic bond has been proposed as one of the early steps in the degradation of anthocyanins, as the resulting aglycone is unstable and undergoes spontaneous ring fission and subsequent degradation (Adams, 1972(Adams, , 1973Clifford, 2000;Markakis, 1974). The presence of phenolic cofactors had also a significant (p = 0.006) influence on the stability of açai fruit anthocyanins in all models.…”

Effects of blackcurrant and apple mash blending on the phenolics contents, antioxidant capacity, and colour of juices

“…This leads to a further loss of anthocyanin colour, since the aglycones are much less stable than their glycosidic forms. It is postulated that the formation of a chalcone is the first step in thermal degradation of anthocyanins (Adams et al 1973). Eventually, thermal degradation leads to brown products, especially in the presence of oxygen.…”

Thermal degradation of anthocyanins and its impact on color andin vitroantioxidant capacity

“…Whereas Markakis (1957) [13] and Hrazdina (1971) [14] postulated opening of the pyrylium ring and chalcone formation as a first degradation step, Adams (1973) [15] proposed hydrolysis of the glycosidic moiety and aglycon formation as the initial reaction. Tanchev and Ioncheva (1976) [16] detected several thermal degradation products, among them quercetin, phloroglucinaldehyde and protocatechuic acid, which were identified by paper chromatography.…”