*3.4. Pigments*

Natural pigments are necessary for photosynthesizing algal metabolism, or macroalgae are divided into three groups depending on pigment content: Phaeophyceae (brown algae), Chlorophyceae (green algae), or Rhodophyceae (red algae) are three families of algae (red algae) [139]. Macroalgae can produce three fundamental types of organic pigments: chlorophylls, carotenoids, or phycobilins [140]. Macroalgae that are wealthy in chlorophylls a or b seem green, whereas algae appear greenish-brown owing to a combination of fucoxanthin (carotenoid), and algae appear red owing to combination of chlorophylls a, c, or d, and phycobilins. Chlorophylls are natural lipid-soluble greenish pigments with porphyrin ring [139]. The chemical structures of different types of pigments in seaweeds are presented in Figure 4.

**Figure 4.** Chemical structures of different types of pigments in seaweeds.

Carotenoids have received much interest and are used in nutritional supplements, fortified foods, animal feed, pharmaceuticals, or cosmetics because of their antioxidant and antimicrobial characteristics, which assist to decrease the prevalence of cardiovascular diseases, ophthalmologic diseases, or cancer [138]. Carotenoids are lipophilic, linear polyenes in two categories: (i) carotenoids, carotenoids, and lycopene; (ii) xanthophylls (e.g., antheraxanthin, zeaxanthin, lutein, fucoxanthin, violaxanthin) [167]. *Ascophyllum nodosum*, *Cladosiphon okamuranus*, *Fucus serratus*, *Chaetoseros* sp., *Ishige okamurae*, *Ecklonia stolonifera*, *Himanthalia elongata*, and *Fucus vesiculosus* all contain carotenoid. It is more efficient upon Gram-positive bacteria (like, *Streptococcus agalactiae*, *Staphylococcus aureus*, *Proteus mirabilis*, *Pseudomonas aeruginosa*, *Staphylococcus epidermidis*, or *Serratia marcescens*) and Gram-negative bacteria (like, *Klebsiella pneumoniae*, *Klebsiella oxytoca*, *Serratia marcescens*, *Acinetobacter lwoffii*, *Pseudomonas aeruginosa* or *Escherichia coli*) [139].

Phycobiliproteins are naturally fluorescent, water-soluble proteins classified as PC (blue pigment), PE (red pigment), and allophycocyanins (light-blue pigment), with PE being most common in several red macroalgae species [139]. Algae rich in phycobiliproteins include *Spirulina*, *Botryococcus*, *Chlorella* and *Nostoc*. These pigments were discovered to have anti-obesity, anti-inflammatory, anti-angiogenic, antioxidant, anti-carcinogenic or neuroprotective activities in a recent study [168]. Table 8 illustrates the role of different carotenoids in human health.


**Table 8.** Summarizes the key activities of carotenoids in human health.


**Table 8.** *Cont.*

Abbreviations: SHP-1: protein tyrosine phosphatase non-receptor type 6; MDA: Malondialdehyde; NO: nitric oxide; APOP: protein oxidation product; GSH: glutathione; CAT: catalase; GST: glutathione S-transeferase; BclxL: antiapoptotic factor; PARP: poly-ADP-ribose polymerase; (VCAM-1, ICAM-1): genes coding for vascular adhesion proteins.
