Thermal Decomposition of Caffeic Acid in Model Systems:  Identification of Novel Tetraoxygenated Phenylindan Isomers and Their Stability in Aqueous Solution

Abstract

Caffeic acid subjected to mild pyrolysis (225−226 °C) under vacuum resulted in rapid decarboxylation and the formation of simple catechol monomers as well as more complex cyclocondensed dimers and polymers. This reaction yielded the same spectrum of products as did acid-catalyzed cyclization of caffeic acid. The major pyrolysis products were identified by reversed-phase HPLC and LC−tandem mass spectrometry. Two novel compounds, identified by MS, 1H NMR, and 13C NMR as 1,3-cis- and 1,3-trans-tetraoxygenated phenylindans, were present as major products in both the caffeic acid pyrolysate and the acid-treated sample. The stability and reactivity of the pyrolysis products in weakly buffered aqueous solutions were determined concomitantly by measuring hydrogen peroxide generation and by monitoring the concentration of the individual components by reversed-phase HPLC. Such model studies may provide information pertaining to reaction mechanisms and the nature of the compounds involved in hydrogen peroxide formation in coffee. Keywords: Pyrolysis; caffeic acid; hydrogen peroxide; phenylindan isomers; model system studies

On-line HPLC analysis of the antioxidant activity of phenolic compounds in brewed, paper-filtered coffee

“…Later in the roasting quinic acid epimerises and lactonises, and several chlorogenic lactones, including 3-and 4-O-caffeoyl-1,5-quinide (figure 5), also form (Scholz and Maier, 1990;Bennat et al, 1994;Schrader et al, 1996;Farah et al, 2005). The cinnamic acids may be decarboxylated and transformed to a number of simple phenols and range of phenylindans probably via decarboxylation and cyclisation of the vinylcatechol intermediate (Stadler et al, 1996). Two of these rather unstable compounds (figure 5) have been found in roasted and instant coffee at 10-15 mg/kg.…”

Nature of hydroxycinnamate-protein interactions

“…2), which will then undergo further reaction (Cilliers and Singleton 1989). Dimers and trimers of caffeic acid (caffeicins and phenylindans) are formed by such reactions involving the side chain of at least one of the caffeic acid units (Cilliers and Singleton 1991;Stadler et al 1996;Arakawa et al 2004). Similarly, the formation of dicaffeoyl quinine, which may be hydrated, was also elucidated (Tazaki et al 2003).…”

Study of acrylamide mitigation in model system: Effect of pure phenolic compounds

“…Moreover, thermal treatment of phenolic acid leads to a rapid decarboxylation yielding vinylpyrocatechol monomers (Rizzi & Boekley, 1992;Tsuji, Shibata, Ohara, Okada, & Ito, 1991). Tetraoxygenated phenylidan isomers were isolated and identified as the major product of caffeic acid pyrolysis at 228°C (Stadler, Welti, Stampfli, & Fay, 1996). Their antioxidative efficacy in a biological rat liver membrane essay was found to be 460-folds higher than that of caffeic acid and approximately 8-folds more than the butylated hydroxytoluene (BHT) (Guillot, Malnoe, & Stadler, 1996).…”