**3.6 Biosynthesis of canthaxanthin**

Canthaxanthin is a carotenoid, and it's one class identified to possess a lot of colouration. Canthaxanthin is biologically synthesized from the precursor, β-carotene, ketolase enzyme (BKT in algae and CRTW in bacteria) serves as the enzyme for the reaction. The allylic 4-position to a carbonyl group is oxidized in the β-ring, producing echinenone as intermediate product. The same enzyme sequentially transforms the 40-carbon atom in the second β-ring to a carbonyl [123, 124]. This is also a substrate for the synthesis of another keto carotenoid astaxanthin which is of commercial interest. The enzyme β-carotene hydroxylase introduces hydroxyl (OH) groups into the canthaxanthin rings at positions 3,30, resulting in astaxanthin formation [125].

### *3.6.1 Pharmacological activities of canthaxanthin*

Antioxidant and free radical scavenging properties [125]. Canthaxanthin alters the onset of many diseases such as cataracts, atherosclerosis, multiple sclerosis, age-related macular degeneration, and cancer [126].

**Figure 1.** *A summary of biological activities and health-promoting properties of biological metabolite.*
