| The stability of coffee flavor compound pyrroles in Fenton-type aqueous solution was investigated. The photooxidation reaction was eliminated as all the experiments were performed in dark space. First, seven pyrroles with various substituents were chosen to discuss their stability in pH5 buffer solution or buffer solution containing Fe (III) (iron) or H2O2 (hydrogen peroxide) at room temperature. The overall result was supportive in studying the losses of pyrroles under Fenton-type reaction at 37°C.The highest loss was 2-ethylpyrrole (2EP), leading up to 98% degradation for 2 days. 6% or less of 1H-, 1-methyl-, 2-ethyl- and 1-furfuryl-pyrrole remained after four day storage. 15.44 +/- 1.78% loss of 2-acetyl-1-methyl-pyrrole was the most stable volatile for four day storage. The systematic studies of degradation influenced by individual or combinational reagents, H 2O2, Fe (III), EDTA (ethylenediaminetetraacetic acid), and ascorbic acid, were investigated. The loss of 2EP in the complete Fenton model reached 88.16 +/- 0.96% after 1 day at 37°C. However, EDTA showed the protective effect on 2EP 10% increase in degradation was observed when EDTA was removed from the system. Also, the highest loss (99.08 +/- 0.08%) of 2EP appeared in the buffer solution which contained Fe (III) and H 2O2. This implied that the equilibrium of Fe (III) and Fe (II) was easily achieved in the co-existence of H2O2. In addition, to extend the stability of pyrrole volatiles, antioxidants, chelating agent and saccharides were applied. 120 muL epicatechin (EC) with concentration at 10 mg/mL, 120 muL epicatechin gallate (ECG) with concentration at 30 mg/mL, and 120 muL chlorogenic acid with concentration at 30 mg/mL all showed the antioxidative property in Fenton-type model system. However, tea polyphenol extract, epigallocatechin (EGC), epigallocatechin gallate (EGCG), L-carnosine, gallic acid, and glutathione each at the concentration of 30 mg/mL, volume 120 muL showed prooxidative property in Fenton-type system. Moreover, the dose-dependent study showed the negative correlation between concentration of chlorogenic acid and radical scavenging activity. 1-Methyl-2,5-pyrrolidinedione, 1,5-dihydro-1-methyl-2-H-pyrrol-2-one, 1-methyl-5-(1-methylpyrrole-2-yl)-2-pyrrolidinone and 1-methyl-5-(1-methylpyrrole-3-yl)-2-pyrrolidinine were identified from 1-methylpyrrole in the reaction of Fenton-type model. No oxidized products were identified from 1H-pyrrole and 2-ethylpyrrole. Their high degradation rate or variation in mechanism from oxidation of 1-methylpyrrole caused the failure of isolating initial reaction product. |
