Effect of oxidative deterioration on flavour and aroma components of lemon oil

Reactions of five major components (citral, α- and β-pinene, limonene and γ-terpinene) of lemon oil in the presence of Cu catalysts and air have been shown to lead to significant oxidation of α- and β-pinene and γ-terpinene, even when the catalyst concentration was comparable to that present in copper-plumbed tap water. Addition of commercial antioxidants (BHA and tocopherol) generally led to suppression of oxidation. UV degradation of these compounds in the presence of air was most significant for γ-terpinene and limonene which gave products similar to those obtained from the Cu-catalysed thermal reactions. Citral gave different products, mainly photocitrals, in contrast to the thermal reactions. The sensitivity of lemon oil to temperature and the presence of air was confirmed.