Phenols and metals in sugar-cane spirits. Quantitative analysis and effect on radical formation and radical scavenging

Abstract.

A fluorescence-based analytical method for quantification of phenolic compounds in sugar cane spirits (and other distilled alcoholic beverages) was developed. Sample preparation involved reverse-phase solid phase extraction and separation by gradient reversed-phase HPLC with fluorescence detection. Twenty-one Brazilian sugar cane spirits (aged and non-aged cachaça) were analyzed and phenol, guaiacol, o-cresol, p-/m-cresol, 3, 5-xylenol, 4-ethylphenol, 4-ethylguaiacol, 2-ethylphenol, eugenol, (+)-catechin, (-)-epicatechin, and scopoletin quantified. The detection limit was between 0.01 mg l^–1 (eugenol and scopoletin) and 0.1 mg l^–1 [(+)-catechin and (-)-epicatechin]. Kaempferol and quercetin were quantified in the same spirits, together with copper and iron, using HPLC (spectrophotometric detection) and atomic absorption spectroscopy, respectively. Large variations between various spirits were noted: total phenols were between 1.5 and 70 mg l^–1, flavonoids were from below detection to 3.5 mg l^–1, Cu was between 0.04 and 7.0 mg l^–1; and Fe between 0.01 and 0.78 mg l^–1. The tendency of radical formation in the spirits was determined by electron spin resonance spectroscopy using N-t-butyl-α-phenylnitrone spin trapping, and radical scavenging capacity was determined spectrophometrically using the stable 2,2-diphenyl-1-picrylhydrazyl radical as probe. Radical formation depends mainly on the Cu content, while the radical scavenging and antioxidative capacity mainly depends on the flavonoid content. (+)-Catechin and (-)-epicatechin are most important for the antioxidative capacity as confirmed in a model experiment, where oxidation was induced by iron catalysis.