Carotenoids as natural functional pigments

Abstract

Carotenoids are tetraterpene pigments that are distributed in photosynthetic bacteria, some species of archaea and fungi, algae, plants, and animals. About 850 naturally occurring carotenoids had been reported up until 2018. Photosynthetic bacteria, fungi, algae, and plants can synthesize carotenoids de novo. Carotenoids are essential pigments in photosynthetic organs along with chlorophylls. Carotenoids also act as photo-protectors, antioxidants, color attractants, and precursors of plant hormones in non-photosynthetic organs of plants. Animals cannot synthesize carotenoids de novo, and so those found in animals are either directly accumulated from food or partly modified through metabolic reactions. So, animal carotenoids show structural diversity. Carotenoids in animals play important roles such precursors of vitamin A, photo-protectors, antioxidants, enhancers of immunity, and contributors to reproduction. In the present review, I describe the structural diversity, function, biosyntheses, and metabolism of natural carotenoids.

Keywords: Biosyntheses; Carotenoids; Function; Metabolism; Natural pigments.

Fig. 1

a Basic structures of carotenoids and end groups. b Structures of typical carotenes and xanthophylls

Fig. 2

a Carotenoid biosynthetic pathways (formation of phytoene). b Desaturation of polyene chain and cyclization of end groups

Fig. 3

Xanthophyll cycles

Fig. 4

a Formation of tobiraxanthin and b formation of pittosporumxanthins in the seeds of Pittosporum tobira

Fig. 5

a Metabolic pathways of fucoxanthin in bivalves and tunicates. b Metabolic conversion mechanisms of end groups of fucoxanthin in bivalves and tunicates

Fig. 6

Metabolic pathways of peridinin in bivalves and tunicates

Fig. 7

Oxidative metabolism of β-carotene in crustaceans

Fig. 8

Metabolic conversion of zeaxanthin to (3S,3′S)-astaxanthin in Cyprinidae fish

Fig. 9

Reductive metabolic pathway of astaxanthin in marine fish

Fig. 10

Food chain and metabolism of carotenoids in sea angel

Fig. 11

Novel carotenoid pyropheophorbide A ester from abalone

Fig. 12

Carotenoid biosynthetic pathways by horizontal transfer genes from fungi and symbiotic bacteria in aphid and whitefly

Fig. 13

Oxidation pathway of xanthophylls with 3-hydroxy-β-end in mammals

Fig. 14

Auto oxidation products of astaxanthin and reaction products of astaxanthin with peroxynitrite

Fig. 15

Reaction products of ataxanthin with hydroxy radicals, superoxide anion radicals, and singlet oxygen