More efficient formation of 10-phenyl-pyranoanthocyanins using 4-vinylphenol
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Date
2021-05
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The Ohio State University
Abstract
Anthocyanins (ACNs) are dietary flavonoids with vivid colors found in plant tissues. ACN-rich juice-concentrates or extracts can be used as food colorant substitutions for artificial ones. Health concerns associated with the consumption of artificial colorants and an increased consumer demand have accelerated the transition towards colorants from natural sources. However, problems arise in the application of ACNs as food colorants due to their limited stability. Pyranoanthocyanins (PACNs) are anthocyanin-derived pigments with enhanced stability that bear a fourth pyran ring in their structure. Hydroxyphenyl–PACNs (HP-PACNs) are a class of PACNs found in wine resulting from the cycloaddition reaction between hydroxycinnamic acids and ACNs. Their synthesis is expensive and time-consuming, restricting their use as colorants by the food industry. We hypothesized that the production of HP-PACNs with 4-vinylphenols, decarboxylated hydroxycinnamic acids, may occur faster. The objectives of this study were to determine the most efficient ACN to 4-vinylphenol molar ratio for production of HP-PACNs and to compare it to its precursor, p-coumaric acid (pCA), under accelerated formation conditions. Black carrot anthocyanins were saponified, diluted in pH 3.1 HCl water and mixed with 4-vinylphenol in molar ratios of 1:1, 1:5, 1:10, 1:20, and 1:30. A positive control of anthocyanins with pCA was prepared at a molar ratio of 1:30. PACN formation and remaining pigment were evaluated after incubation at 45°C for 24 hours in the dark using HPLC-PDA-ESI-MS/MS analyses. PACN production with 4-vinylphenol was at least 34 times greater (p<0.05) than with pCA (~0.5%). Moreover, PACN yields with 4-vinylphenol at a molar ratio of 1:5 (~37%), 1:10 (~40%) and 1:20 (~35%) were significantly higher than with 1:1 (~14%) and 1:30 (~29%). 4-vinylphenol in a ratio of 1:5 and 1:10 had higher content of pigment remaining (~40%) than the anthocyanin without cofactor (~23%) but lower than with pCA (~46%). Overall, formation of PACNs using 4-vinylphenols was faster than with pCA, yielding ~40% PACN in only 24 hours and requiring less cofactor (1:10). Ultimately, this will facilitate the transition from synthetic colorants to naturally derived alternatives for the food industry.
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Keywords
Anthocyanin, Pyranoanthocyanin, Cofactor, 4-vinylphenol, p-coumaric acid