Natural Colours in Food Products
By Michal Kazmirsky EUR ING, Akuna R & D and Lab Manager
Polyphenols are a large and complex group of bioactive compounds that are naturally occurring in fruit, vegetables, chocolate, and beverages like wine and tea. One of the major groups of phenols is flavonoids - a large family of thousands hydroxylated polyphenolic compounds that carry out important functions in plants, including attracting pollinating insects; combating environmental stresses, such as microbial infection; and regulating cell growth.
One of the 12 major subclasses of flavonoids are anthocyanidins. Anthocyanidins with one or more sugar moieties – anthocyanidin glycosides – are called anthocyanins. Anthocyanins are natural colours – the only phenolics with the positive charge that gives the molecule its colour. The highest quantity of the anthocyanin pigments occurs in red, purple and blue berries, red and purple grapes, and red wine. Anthocyanin pigments are not just natural colorants; due to their bioactive properties, they are also compounds with considerable health benefits including: reduced risk of coronary heart disease, reduced risk of stroke, anticarcinogen activity, anti-inflammatory effects, improved visual clearness, and improved cognitive behavior.
The different anthocyanins can vary considerably with respect to their stability and colour properties. Their natural variation in colour intensity and hue, as well as their stability, is a result of their structural variation, with hundreds identified in nature. The matrix in which the anthocyanin pigments exist can have a great impact on pigment transformation, as well. There are a number of factors that cause their instability, including their sensitivity to light and heat, as well as their reaction to the occurring structural transformations.
Colour and chemical properties of anthocyanins are also markedly affected by pH and this factor should be considered as a major impact on colour for many food applications. Anthocyanins reversibly undergo structural transformation with change in pH. At pH 1.0 the predominant form is the oxonium form (Flavylium Cation), which is coloured: orange to purple. The hemiketal form (Carbonyl pseudo-base) and Chalcone are predominant at pH 4.5 and are colourless. At pH 7.0 the predominant form is Quinoidal base: blue colour.
These structural transformations of anthocyanin pigments with the change in pH are very important to understand, since they explain the natural colour variations in all food applications. Despite those variations, there is an increase in the use of anthocyanin colorants in dietary consumption because of their possible health benefits. Anthocyanin pigments are very potent free radical scavengers and antioxidants that are associated with the prevention of age-related disorders.
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