The chemistry and analysis of annatto food colouring: a review

Michael Scotter (1)

1 CSL - DEFRA Central Science Laboratory

Annatto food colouring (E160b) has a long history of use in the food industry for the colouring of a wide range of food commodities. The principle colouring components of annatto is the oil-soluble diapo carotenoid bixin, which is the methyl ester of the dicarboxylic acid norbixin, which is soluble in aqueous alkali. Bixin and norbixin therefore exhibit not only physicochemical properties normally associated with carotenoids but also certain anomalous properties that have an impact on the stability, food colouring applications and importantly the analysis of annatto. This review summarizes the key aspects of the structural determination of bixin (and norbixin) with special attention to cis-trans isomerization and how this links with its chemical structure, spectroscopic properties and stability. The oxidative, thermal and photo stability of annatto and the subsequent implications for its use in the colouring of foods, food processing, and the analysis of foods and beverages are discussed along with important mechanistic, thermodynamic and kinetic aspects. The main analytical techniques used for the chemical characterization of annatto i.e. spectrophotometry, NMR, chromatography (particularly HPLC) and mass spectrometry are reviewed in detail and other methods discussed. This links in with a review of the methods available for the detection and measurement of annatto in colour formulations and foods and beverages, which highlights the importance of the need for a good understanding and knowledge of the chemistry of bixin and norbixin in order to meet new analytical challenges.

Mots clés: Life Sciences

Michael Scotter. The chemistry and analysis of annatto food colouring: a review. Food Additives and Contaminants, 2009, 26 (08), pp.1123-1145. ⟨10.1080/02652030902942873⟩. ⟨hal-00573911⟩