3.5 Other biopolymers

Algenanes are aliphatic, nonhydrolyzable, and insoluble biopolymers found in the ECM at 9 and 10% dry weight of race A and B, respectively. Due to their high resistance to degradation, they are attributed to the good preservation of colonies in sedimentary rocks [108].

Another reported biopolymer was the polyhydroxybutyrate (PHB), a biodegradable plastic with a yield of about 20% of the dry weight [109]. PHB is a polyester with thermoplastic and biodegradable properties, and it's a carbon and energy storage compound. For its similar physical properties to polypropylene and polystyrene, it is of commercial interest [110]. Under pH 7.5, 40°C, and with 60% wastewater as culture medium, a maximum yield of 247 0.42 mg/L PHB was reported [111].

3.3 Pigments

BOT22 (B)

BOT84 (L)

> BOT7 (S)

mg/cm2 . <sup>b</sup> mg/cm2 /day.

Table 3.

Biofilm bioreac.

Microalgae - From Physiology to Application

astaxanthin [85–87].

[94, 95].

132

3.4 Polysaccharides

Algae pigments have been reported to have antioxidant, anticancer, antiinflammatory, antiobesity, and antiangiogenic properties and function as neuroprotectives [85]. So, they could replace synthetic dyes in food, cosmetic,

St System TRT Biomass Lipids Ref.

CNT, content (% DW dry weight); Chu, Chu media for microalgae [8]; EF, Erlenmeyer flask; FBR, photobioreactor; N:P, proportion of nitrogen: phosphate; Px, biomass productivity (g/L day); NIA, no information available; Prod., productivity (g/L day); Rcwy, raceway; SCGR, specific cell growth rate (μ/day); μ, specific velocity of growth rate; St,

strain (race); TRT, treatment; Yld., yield (g/L); Xmax, maximum cellular concentration (g/L). <sup>a</sup>

Nitrocell. Memb. (diam. 25 mm and pore size 0.45 μm)

SCGR XMax Px CNT Yld. Prod.

NIA 10.04<sup>a</sup> 3.8<sup>b</sup> NIA 1.11<sup>a</sup> NIA

NIA 13.6<sup>a</sup> 0.99<sup>b</sup> NIA 0.83<sup>a</sup> NIA

NIA 3.12a 0.42<sup>b</sup> NIA 0.83<sup>a</sup> NIA [84]

Carotenoid pigments are unsaturated hydrocarbons, while xanthophylls have one or more functional groups containing oxygen such as lutein, canthaxanthin, and

Carotenoids abound in races B and L, lutein being the main pigment (22–29%), followed by others as β-carotene, echinenone, 3-OH echinenone, canthaxanthin, violaxanthin, loroxanthin, and neoxanthin. Transition to stationary phase causes a color change in B. braunii from green to brown, reddish orange, and pale yellow by accumulation of carotenoids and a decrease of intracellular pigments [88]. Can-

stationary phase in response to nitrogen deficiency [36]. The BOT-20 strain showed a dark red color during growth because of the accumulated echinenone of about 30.5% dry weight and 630 mg/L production, but with few hydrocarbons (8%) [89]. Adonixanthin was detected in race L during the stationary phase [90], and botryoxanthin A, botryoxanthin B, and braunixanthin 1 and 2 were detected in race B [37, 38, 91]. The 2-azahypoxanthine (AHX) similar to the phytohormone induced the accumulation of secondary carotenoids like botryoxanthin A and braunixanthin 1 and decreased the content of botryococcenes during the stationary phase [92],

In race A, lutein (79–84%) is the main carotenoid followed by β-carotene (1.75– 2.14%), violaxanthin (6–9%), astaxanthin (3–8%), and zeaxanthin (0.32–0.78%). In salinity and high light intensity conditions, the lutein increases [53, 93]. All of these compounds shown antioxidant properties and inhibitory effect against lipid peroxidation in vitro and in vivo and activated antioxidant enzymes such as catalase

The aqueous extracts of B. braunii (strain LB 572) reduce the skin dehydration,

stimulate collagen synthesis, promote the differentiation of adipocytes, and

thaxanthin (46%) and echinenone (20–28%) are predominant in the

imitating a lack of nitrogen condition without inhibiting the growth.

nutraceutical, and pharmaceutical products [86].

Comparison of crop conditions and lipid productivity in B. braunii.

B. braunii (UTEX 572) was used to produce intra- and extracellular Ag nanoparticles (AgNPs) with antimicrobial properties, and analysis suggested that the exopolysaccharides were the possible reducing and capping agents [112].
