in Figure 2. This is a different species from G.jasminoides, but the flavonoid compounds in closely related species tend to be similar. The flavonoids would contribute a pale yellow color and the carotenoids an orange color.
The iridoid pigments constitute an interesting situation as a food colorant because a range of colors from green to yellow, red and blue, can be produced (1). The patent literature suggests extraction of the fruit with water, treatment with enzymes having /f-glycosidic or proteolytic (bromelain) activity, followed by reaction with primary amines from amino acids or a protein such as soy. The reaction conditions such as time, pH, temperature, oxygen content, degree of polymerization, and conjugation of the primary
1. F. J. Francis, "Less Common Food Colorants," in G. A. F. Hendry and J. D. Houghton, eds., Natural Food Colorants, Blackie Publishers, Glasgow, Scotland, 1996, pp. 310-342.
Monascus products have been well known in south and east oriental countries for centuries. Wong and Koehler listed their use as a Chinese medicine as far back as 1590 (1). The genus Monascus includes several fungal species that will grow on a number of carbohydrate substrates, especially steamed rice. Traditionally, Monascus species were grown on rice, and the whole mass was eaten as an attractive red food. It could also be dried, ground, and incorporated into other foods.
Monascin R = C5H11 Ankaflavin R = C7H15
Figure 1. Pigments of Monascus.
COLORANTS: PHYCOBILINS 399
Monascus species produce six pigments with the structures shown in Figure 1. Monascin and ankaflavin are yellow, rubropunctatin and monascorubin are red, and rub-ropunctamine and monascorubramine are purple. The red and yellow pigments are considered to be normal secondary metabolites of fungal growth, and the purple pigments may be formed by enzymatic modification of the red and yellow pigments. The red pigments are very reactive and readily react with amino groups via a ring opening and a SchifF rearrangement to form water-soluble compounds such as that in Figure 2 (2). The Monascus pigments have been reacted with amino groups, polyamino acids, amino alcohols, chitin amines or hexamines, proteins, peptides and amino acids, sugar amino acids, browning reaction products, aminoacetic acid, and amino benzoic acid (3). Obviously a number of derivatives are possible, and they have been shown to have greater water solubility, thermostability, and photostability than the parent compounds.
The Monascus pigments are readily soluble in ethanol and only slightly soluble in water. Ethanolic solutions are orange at pH 3 to 4, red at 5 to 6 and purplish red at 7 to 9. The pigments fade under prolonged exposure to light, but the pigments in 70% alcohol are more stable than in water. The pigments are very stable to temperatures up to 100°C in neutral or alkaline conditions.
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