460 DAIRY CHEMISTRY AND BIOCHEMISTRY
HOOC\
BixinLOOCH,HOOC
Norhixincoon
Figure 11.8 Structures of cis-bixin and norbixin, apocarotenoid pigments in annatto.The colour of dairy products such as butter and cheese is due to
fat-soluble pigments, especially carotenoids, which are not synthesized by
the animal but are obtained from plant sources in the diet. Therefore, feed
has a major effect on the colour of milk-fat. Cows fed on grass produce a
more yellow-coloured fat than animals fed on hay or concentrates. The
ability of cattle to metabolize carotenes to vitamin A varies between breeds
and between individuals (Chapter 6).
The most widely used added colorant in dairy products is annatto
(E160b) which is a yellow-orange preparation containing apocarotenoid
pigments obtained form the pericarp of the seeds of the tropical shrub, Bixa
orellana. The principal pigment in annatto is cis-bixin (methyl 9’-cis-6,6‘-
diapocarotene-6,6’-diooate) with smaller amounts of norbixin (cis-6,6-dia-
pocarotene-6,6’-dioic acid) (Figure 113). The heat treatment used in extrac-
tion normally converts cis-bixin to trans-bixin which is red and soluble in
oil. Annatto is used to give a yellow colour to margarine and to colour ‘red’
Cheddar and other cheeses.
References
IDF (1983) Measurement of extraneous water by the freezing point test, Bulletin 154, Interna-
tional Dairy Federation, Brussels.
Jenness, R. and Patton, S. (1959) Principles of Dairy Chemistry, John Wiley and Sons, New
York.
Mulvihill, D.M. (1992) Production, functional properties and utilization of milk protein
products, in Aduanced Dairy Chemistry, Vol, 1: Proteins, (ed. P.F. Fox), Elsevier Applied
Science, London, pp. 369-404.
Rattray, W. and Jelen, P. (1996) Thermal stability of skim milk with protein content
standardized by the addition of ultrafiltration permeates. lnt. Dairy J., 6, 157-70.