Abstract:
Phenolic compounds are important components of grapes and wines. They have been found
to have important roles in grape and wine systems and properties that are beneficial for human
health. Vanillin (3-methoxy-4-hydroxybenzaldehyde) is a phenolic compound coming from the
oxidative degradation of lignin in oak-barrels during the aging of wine. Vanillin is an important
flavour component of wine and its concentration in wine influences significantly the aroma and
flavour of wine. The concentration of vanillin in wine is affected by various factors including the
presence of metal ions. In this work, by using HPLC, HPLC-MS, and MS technologies, iron (III)
cations were found to affect the oxidation of vanillin in a model system of wine, and the product
of the oxidation was identified as divanillin. The mechanism of the redox reaction between
vanillin and Fe^"^ is thought to follow that of other phenol oxidations. Increasing the
concentration of Fe ^ in the model system accelerates divanillin production. The best pH
condition for the divanillin production in the system is the range of 3.0 ~ 3.5. Increasing
temperature from 20°C to 40°C accelerates the divanillin production. Divanillin was found to
exist in three commercial red wines in this work. Keeping the storage temperature cool and
decreasing the contact of grapes and wines with iron are two major measures suggested by this
work in order to decrease the oxidation of vanillin during the making and aging of wine.
