Bioactive compounds with diverse chemical structures play a significant role in disease prevention and maintenance of physiological functions. Due to the increase in industrial demand for new biosourced molecules, several types of biomasses are being exploited for the identification of bioactive metabolites and techno-functional biomolecules that are suitable for the subsequent uses in cosmetic, food and pharmaceutical fields. Among the various biomasses available, macroalgae are gaining popularity because of their potential nutraceutical and health benefits. Such health effects are delivered by specific diterpenes, pigments (fucoxanthin, phycocyanin, and carotenoids), bioactive peptides and polysaccharides. Abundant and recent studies have identified valuable biological activities of native algae polysaccharides, but also of their derivatives, including oligosaccharides and (bio)chemically modified polysaccharides. However, only a few of them can be industrially developed and open up new markets of active molecules, extracts or ingredients. In this respect, the health and nutraceutical claims associated with marine algal bioactive polysaccharides are summarized and comprehensively discussed in this review.

Phycobiliproteins are photosynthetic light-harvesting pigments isolated from microalgae with fluorescent, colorimetric and biological properties, making them a potential commodity in the pharmaceutical, cosmetic and food industries. Hence, improving their metabolic yield is of great interest. In this regard, the present review aimed, first, to provide a detailed and thorough overview of the optimization of culture media elements, as well as various physical parameters, to improve the large-scale manufacturing of such bioactive molecules. The second section of the review offers systematic, deep and detailed data about the current main features of phycobiliproteins. In the ultimate section, the health and nutritional claims related to these bioactive pigments, explaining their noticeable potential for biotechnological uses in various fields, are examined.

This study aimed to maximize biomass concentration, biomass productivity and biochemical composition of the marine microalga Tetraselmis sp. In the current study, Box-Behnken Design was used to model the effect of NaNO3, NaH2PO4, metals and vitamins in the F/2 medium on the growth, total chlorophylls, carotenoids and starch contents. The total chlorophylls content was quantified by spectrophotometry. The FT-IR spectroscopy was used to estimate the biochemical compositions of Tetraselmis sp. grown under both optimized medium culture for starch production and standard culture medium. Finalized NaNO3 (1.76 mM), NaH2PO4 (0.018 mM), metals (1500 μL.L−1) and vitamins (312.5 μL.L−1) concentrations, generated an increase in biomass concentration up to 5.72 g.L−1 which contributed to an increase about 2.4-fold than that of the standard conditions of biomass productivity (408.57 mg.L−1.day−1). The maximum value of carotenoids content (0.3 mg.g DW−1) was achieved at the highest level of all factors. The total chlorophylls content reached also its maximum (5.18 mg.g DW−1) at high nitrate (1.76 mM), phosphate (0.054 mM), metals and vitamins concentrations, while the maximum starch content (42% DW) was achieved with low nitrate and phosphate concentrations (0.58 mM and 0.027 mM) and with metals and vitamins limitations. Thus, the nitrogen, phosphorus, metals and vitamins limitations led to divert the metabolism for the starch biosynthesis. The high biomass concentration productivity and starch production make Tetraselmis sp. strain a good candidate for biotechnological applications.

Polysaccharides from marine algae are one novel source of plant defense elicitors for alternative and eco-friendly plant protection against phytopathogens. The effect of exopolysaccharides (EPS) produced by Porphyridium sordidum on elicitation of Arabidopsis thaliana defense responses against Fusarium oxysporum was evaluated. Firstly, in order to enhance EPS production, a Box–Behnken experimental design was carried out to optimize NaCl, NaNO₃ and MgSO₄ concentrations in the culture medium of microalgae. A maximum EPS production (2.45 g/L) higher than that of the control (0.7 g/L) was observed for 41.62 g/L NaCl, 0.63 g/L NaNO₃ and 7.2 g/L MgSO₄ concentrations. Structurally, the EPS contained mainly galactose, xylose and glucose. Secondly, the elicitor effect of EPS was evaluated by investigating the plant defense-related signaling pathways that include activation of Salicylic or Jasmonic Acid-dependent pathway genes. A solution of 2 mg/mL of EPS has led to the control of fungal growth by the plant. Results showed that EPS foliar application induced phenylalaline ammonia lyase and H₂O₂ accumulation. Expression profile analysis of the defense-related genes using qRT-PCR revealed the up-regulation of Superoxide dismutases (SOD), Peroxidase (POD), Pathogenesis-related protein 1 (PR-1) and Cytochrome P450 monooxyge-nase (CYP), while Catalase (CAT) and Plant defensin 1.2 (PDF1.2) were not induced. Results suggest that EPS may induce the elicitation of A. thaliana’s defense response against F. oxysporum, activating the Salicylic Acid pathway.

Lately, microalgae have been used as natural additives in fish-transformed products to improve their nutritional quality. In this research, the effects of adding Spirulina platensis at concentrations of 0.5, 1 and 1.5% w/v on both the texture and the sensory characteristics of canned burgers were studied. In fact, the addition of Spirulina platensis to fish burgers improves their nutritional composition. Compared to the results of the other fish burger treatments, the treatments that contain 1% of Spirulina platensis had better texture and sensory properties (p < 0.05). Besides, these treatments showed higher swelling ability as well as water and oil holding capacities, due to the important dietary fibers and polysaccharides contents found in Spirulina platensis. No mold or foodborne pathogens were detected in any of the canned burgers up to 8 months of storage at 4 °C. Furthermore, burgers prepared with Spirulina were distinguished by the lowest mean (a* and b*) values (p < 0.05), which shows that the yellow color gradually diminished towards a greenish color. Because of the presence of polysaccharides and pigments (chlorophylls, carotenoids and phycocyanin), Spirulina platensis considerably ameliorates the antioxidant activities of the newly prepared fish burgers. On the whole, we can conclude that Spirulina platensis can be used as a nutritious additive to produce new fish-based products with high alimentary qualities.