Isomerization of all-trans-β-carotene and formation of 13-cis- and 9-cis-β-carotene in plain carrot puree during thermal processing (80–150°C) has been described by a fractional conversion model, which is characterized by a plateau value after prolonged heating (Lemmens et al., 2010). As β-carotene isomerization is a reversible reaction (Dugave, 2006), the isomerization reaction from alltrans-β-carotene to the cis-isomers is in equilibrium with the reverse reaction at the moment the plateau is reached