The safety assessment of a flavour substance examines several factors, including metabolic and physiological
disposition data. The present article provides an overview of the metabolism and disposition of flavour substances
by identifying general applicable principles of metabolism to illustrate how information on metabolic fate is taken
into account in their safety evaluation. The metabolism of the majority of flavour substances involves both a series
of enzymatic and non-enzymatic biotransformation that often result in products that are more hydrophilic and more
readily excretable than their precursors. Flavours can undergo metabolic reactions, such as oxidation, reduction, or
hydrolysis that alter a functional group relative to the parent compound. The altered functional group may serve as a
reaction site for a subsequent metabolic transformation. Metabolic intermediates undergo conjugation with an
endogenous agent such as glucuronic acid, sulphate, glutathione, amino acids, or acetate. Such conjugates are
typically readily excreted through the kidneys and liver. This paper summarizes the types of metabolic reactions that
have been documented for flavour substances that are added to the human food chain, the methodologies available
for metabolic studies, and the factors that affect the metabolic fate of a flavour substance.