*4.1. Chemical Structure and Mechanism of Action*

Fucoxanthin is a naturally occurring brown pigment that belongs to the class of non-provitamin A carotenoids, a class of 40-carbon organic molecules that consist of two groups: xanthophylls if their structure contains oxygen, and carotenes if there is no oxygen in their chemical formula. Fucoxanthin is a xanthophyll whose distinct structure includes an unusual allenic bond, epoxide group and conjugated carbonyl group in polyene chain [33] with antioxidant properties [34]. The difference, however is that fucoxanthin acts as an antioxidant under anoxic conditions whereas other carotenoids have practically no quenching abilities. Most tissues under physiological conditions have low oxygen presence. Furthermore, the typical antioxidants are usually proton donors (ascorbic acid, ΅-tocopherol, glutathione). Fucoxanthin, on the other hand, donates electron as a part of its free-radical quenching function. A combination of these distinct properties is very rarely found among naturally occurring food-derived compounds [35,36]. During normal metabolism the body produces heat. Fucoxanthin increases the amount of energy released as heat in fat tissue, a process also called thermogenesis. A published study reports that fucoxanthin affects multiple enzymes involved in fat metabolism causing an increase in the production of energy from fat [37]. 
