Ascorbic acid-catalyzed degradation of cyanidin-3-O-β-glucoside: Proposed mechanism and identification of a novel hydroxylated product

Abstract

Abstract. BACKGROUND:Many brightly colored fruits and vegetables owe their pigmentation and beneficial health effects to anthocyanins. Unfortunately, anthocyanins in the presence of ascorbic acid are readily degraded over juice processing and storage, which adversely affects color stability and potential health benefits. OBJECTIVE: This project focused on the effect of ascorbic acid as a catalyst in anthocyanin degradation. METHODS:The project involved searching for novel pigmented compounds in a simple model system composed of the most common anthocyanin cyanidin-3-O-␤-glucoside and ascorbic acid, and a second model system consisting of blackberry extract supplemented with ascorbic acid. Degradation products were identified by HPLC-PDA and HPLC-MS. ESR was used to monitor hydroxyl radical formation in the model systems. RESULTS: Over 72 hours at ambient temperature, 67% of cyanidin-3-O-␤-glucoside was lost in the model system during which time an unknown pigmented compound was formed. The unknown compound was also formed in a more complex model system consisting of blackberry extract and ascorbic acid. HPLC with PDA monitoring at 510 nm was used to detect a novel compound and HPLC-ESI-MS 3 allowed a proposed structure to be built based on the fragmentation patterns. The unknown structure formed via oxidation of cyanidin 3-O-␤-glucoside by ascorbic acid was identified as 6-hydroxy-cyanidin-3-O-␤-glucoside. The mechanism was substantiated with malvidin-3-O-␤-glucoside and ascorbic acid, which produced a hydroxylated malvidin-3-O-␤-glucoside. Production of hydroxyl radical in the base and blackberry model systems was confirmed by ESR. CONCLUSIONS: We propose that the pigmented compound is formed from hydroxyl radicals via the Haber-Weiss reaction. The addition of food grade hydroxyl radical scavengers to juices may be a viable treatment to prevent ascorbic acid-catalyzed degradation of anthocyanins.

Influence of supplementing red wine with oak staves of various ellagitannin release potentials and different micro-oxygenation doses on wine colour and phenolic and volatile composition

“…As expected, the total anthocyanin concentration decreased over time when MOX was applied, and this decrease was greater when the oxygen dose was higher. These data confirm that oxygen can degrade anthocyanins, as has been reported before (King et al, 1980). However, the PVPP index tended to increase over time in all of the MOX wines, and did so more rapidly when the higher oxygen dose was applied.…”

Recent Research on the Health Benefits of Blueberries and Their Anthocyanins

“…During juice and purée processing, heat, oxygen, and enzymes can degrade blueberry phytochemicals, with greatest losses to vitamin C and anthocyanins. Blueberries are low in ascorbic acid and high in anthocyanins ( 187 ), and notably anthocyanins are readily degraded by ascorbic acid ( 188 , 189 ).…”

Investigating the Interaction of Ascorbic Acid with Anthocyanins and Pyranoanthocyanins

“…Ascorbic acid could form hydrogen peroxide which then could react with the pyranoanthocyanin, but the typical result would involve loss of color, and we would expect a different mass transition. Stebbins et al [ 31 ] reported the formation of 6-hydroxy-cyanidin-3-glucoside from cyanidin-3-glucoside and ascorbic acid, the transitional m / z being +16 mass units. A different mechanism probably occurs, possibly related to the condensation of the pyranoanthocynin with other AA degradation products, and perhaps even the rearomatization of the molecule.…”