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J AOAC Int. 2000 Sep-Oct;83(5):1135-40.

Hydrolysis and redox factors affecting analysis of common phenolic marker compounds in botanical extracts and finished products.

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1
Industrial Laboratories, Research and Development, Denver, CO 80216, USA.

Abstract

Many of the marker compounds analyzed in herbal products are redox-active phenolic molecules, which are commonly found in plants as components of glycosides and starch polymers. Variability in degree of sample hydrolysis can occur due to differences in water content, pH, and temperature. Sonication versus shaking during extraction can also influence hydrolysis and oxidation of sensitive compounds. Some traditional botanical extract marker compounds are esters and glycosides of phenolics such as echinacoside from Echinacea while others are free phenolics, such as quercetin from glycosides in Ginkgo. Optimizing hydrolysis conditions maximizes free quercetin levels, but lowers echinacoside levels. Furthermore, acidic hydrolysis conditions mimic stomach conditions encountered by oral supplements and protect resulting free phenolics from oxidation. Oxidative degradation of botanical phenolic markers can be initiated by light, sonication, oxygen, basic pH conditions, heat, redox-active solvents, and formulation additives. Some phenolic markers reversibly cycle through multiple oxidation states creating a formula-specific equilibrium of oxidation states. Finished product formulations that include easily oxidized phenolics, carbonates, phosphates, and transition metals affect sample hydrolysis degree and redox equilibria, and quantitation. By recognizing and controlling hydrolysis and oxidation variables, more accurate and rugged methods can be developed allowing for improved botanical standardization and finished product analysis.

PMID:
11048854
[Indexed for MEDLINE]

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