Natural food and beverage colourings - Natural Food Additives, Ingredients and Flavourings - page 30

are fermented to alcohol. The extract is concentrated by vacuum evaporation
during which practically all of the alcohol is removed. A small amount of sulphur
dioxide may be present.
Black carrots are gown in Turkey and Northern Europe and extracted by an
aqueous process and concentrated by a combination of low pressure evaporation
and membrane fi ltration. Commercial forms are sold on colour strength as
determined by their anthocyanin content. Grapeskin anthocyanins are normally
sold as a 1% water-soluble liquid containing sorbate or benzoate as a preservative
or a 4% spray-dried powder on maltodextrin. Black carrot is traditionally sold as
either a 3% water-soluble liquid or a 4% spray-dried powder on maltodextrin.
The color of anthocyanins is pH dependent. The anthocyanin system undergoes
mostly reversible transformations as the pH changes. Essentially anthocyanins
exist as fi ve different chemical moieties in equilibrium: red fl avylium cation;
colourless carbinol pseudo base; purple quinoidal base; blue quinoidal base anion;
and yellowish chalcone. These are the classic colours from pH indicator colours
and indeed red cabbage was originally impregnated into paper to form one of the
fi rst indicator papers.
Anthocyanin-based food colours are most stable at low pH (below pH 3.5),
where they give the red colour based on the fl avylium cation. By using
anthocyanins as food colours it has often been diffi cult to replicate the shades
found within nature. This is because within natural systems anthocyanins
undergo co-pigmentation with polyphenols such as fl avones and fl avonols, and
'intramolecular sandwich-type stacking'. 8 In addition, metal complexation seems
to be chiefl y responsible for blue fl ower colouration. Specifi cally it has been
found that the molecular structure of the cornfl ower pigment (protocyanin
complex) comes from the arrangement of four metal ions (one ferric iron, one
magnesium and two calcium ions), which bind a complex of six molecules each
of a succinyl anthcyanin and a malonylfl avone (co-pigment). 9,10 The colour shade
varies between the exact botanical sources used for the anthocyanins but in reality
year-to-year variations are moderated by the natural colour companies by blending
of stocks to minimise the impact on their customers.
In a low pH application, grapeskin extract is a burgundy red colour whereas
black carrot extract has less blue notes and is a more strawberry colour. Apart
from the shade, the main difference between fruit and vegetable forms of
anthocyanin is their stability to pH change. Typically fruit-based sources of
anthocyanins such as grapeskin extract will not give a stable colour at neutral pH.
If grapeskin extract is added to milk it will rapidly turn grey and form a precipitate.
However, if a vegetable sourced anthocyanin such as black carrot or red cabbage
is added to milk a stable mauve/purple colour is formed. Typical applications for
anthocyanins are soft drinks, confectionary and fruit preparations where an acidic
pH exists.
It is possible to take advantage of the pH shade change to create a blue
anthocyanin formulation. This can be done by adjusting the pH of the extract to
approximately pH 7-7.5 and then drying to fi x the colour of the formulation. It is
necessary to dry because of the loss of stability at higher pH values, which can be

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