The chemistry and analysis of annatto food colouring: a review

Abstract

International audienceAnnatto 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

Analysis of Residual Solvents in Annatto Extracts Using a Static Headspace Gas Chromatography Method

“…These may also be residue of solvents used in the manufacturing process, although the methanol might be generated by hydrolysis of the methylester in bixin during storage. Scotter et al reported the powdered bixin is more unstable than oleoresin bixin and gradually degrades in complex reactions, even in dark and cold conditions [1]. In fact, bix4 was stored for a few years before used in this study.…”

“…Annatto extracts are natural yellowish-orange colorants prepared from the seeds of the tropical tree Bixa orellana L. [1]. Annatto extracts have good heat stability during food processing and have been used in many countries to give a yellow-to-red color to foods, especially dairy products such as butter and cheese [1].…”

“…Annatto extracts have good heat stability during food processing and have been used in many countries to give a yellow-to-red color to foods, especially dairy products such as butter and cheese [1]. The principle pigments of annatto extracts are apocarotenoids, bixin, and norbixin [2] (Figure 1).…”

“…Bixin is lipophilic in nature and therefore highly insoluble in water. Therefore, crude extracts containing bixin are often hydrolyzed with an alkali to prepare norbixin in order to increase the water solubility of the pigments [1,2]. The salts of norbixin obtained by alkali hydrolysis are soluble in water, however, the protonated form of norbixin formed after acid-precipitation purification becomes insoluble (Figure 2).…”

Natural antioxidants as stabilizers for polymers

“…Lipid oxidation leads to unsavory odor, color, taste and altered texture of food products, which can be hindered by the proper application of antioxidants [52]. Carotenes are usually applied as natural yellow, orange or red colorants in various foods like cakes, sauces, marinades, spice blends, beverages and dairy products [53]. Carotenes are rarely applied alone because of their sensitivity towards oxygen and ultraviolet radiation leading to undesired color loss [54].…”