Microalgae for high-value compounds and biofuels production: a review with focus on cultivation under stress conditions.

Spirulina is a species of filamentous cyanobacteria that has long been used as a food supplement. In particular, Spirulina platensis and Spirulina maxima are the most important. Thanks to a high protein and vitamin content, Spirulina is used as a nutraceutical food supplement, although its other potential health benefits have attracted much attention. Oxidative stress and dysfunctional immunity cause many diseases in humans, including atherosclerosis, cardiac hypertrophy, heart failure, and hypertension. Thus, the antioxidant, immunomodulatory, and anti-inflammatory activities of these microalgae may play an important role in human health. Here, we discuss the antioxidant, immunomodulatory, and anti-inflammatory activities of Spirulina in both animals and humans, along with the underlying mechanisms. In addition, its commercial and regulatory status in different countries is discussed as well. Spirulina activates cellular antioxidant enzymes, inhibits lipid peroxidation and DNA damage, scavenges free radicals, and increases the activity of superoxide dismutase and catalase. Notably, there appears to be a threshold level above which Spirulina will taper off the antioxidant activity. Clinical trials show that Spirulina prevents skeletal muscle damage under conditions of exercise-induced oxidative stress and can stimulate the production of antibodies and up- or downregulate the expression of cytokine-encoding genes to induce immunomodulatory and anti-inflammatory responses. The molecular mechanism(s) by which Spirulina induces these activities is unclear, but phycocyanin and β-carotene are important molecules. Moreover, Spirulina effectively regulates the ERK1/2, JNK, p38, and IκB pathways. This review provides new insight into the potential therapeutic applications of Spirulina and may provide new ideas for future studies.

The antioxidant, immunomodulatory, and anti-inflammatory activities of Spirulina: an overview

Microalgae are microorganisms that have different morphological, physiological, and genetic traits that confer the ability to produce different biologically active metabolites. Microalgal biotechnology has become a subject of study for various fields, due to the varied bioproducts that can be obtained from these microorganisms. When microalgal cultivation processes are better understood, microalgae can become an environmentally friendly and economically viable source of compounds of interest, because production can be optimized in a controlled culture. The bioactive compounds derived from microalgae have anti-inflammatory, antimicrobial, and antioxidant activities, among others. Furthermore, these microorganisms have the ability to promote health and reduce the risk of the development of degenerative diseases. In this context, the aim of this review is to discuss bioactive metabolites produced by microalgae for possible applications in the life sciences.

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Biologically Active Metabolites Synthesized by Microalgae

Microalgae can be regarded as an alternative and promising food ingredient due to their nutritional composition, richness in bioactive compounds, and because they are considered a sustainable protein source for the future. The aim of this work was to evaluate microalgae ( Arthrospira platensis F&M-C256, Chlorella vulgaris Allma, Tetraselmis suecica F&M-M33 and Phaeodactylum tricornutum F&M-M40) as innovative ingredients to enhance functional properties of cookies. Two biomass levels were tested and compared to control: 2% (w/w) and 6% (w/w), to provide high levels of algae-bioactives. The cookies sensory and physical properties were evaluated during eight weeks showing high color and texture stability. Cookies prepared with A. platensis and C. vulgaris presented significantly ( p A. platensis cookies were preferred. Besides, A. platensis also provided a structuring effect in terms of cookies texture. All microalgae-based cookies showed significantly higher ( p in vitro antioxidant capacity compared to the control. No significant difference ( p in vitro digestibility between microalgae cookies and the control was found.

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Microalgae biomass as an alternative ingredient in cookies: Sensory, physical and chemical properties, antioxidant activity and in vitro digestibility

In a minute proportion of angiosperm species, rehydrating foliage can revive from airdryness or even from equilibration with air of ~0% RH. Such desiccation tolerance is known from vegetative cells of some species of algae and of major groups close to the evolutionary path of the angiosperms. It is also found in the reproductive structures of some algae, moss spores and probably the aerial spores of other terrestrial cryptogamic taxa. The occurrence of desiccation tolerance in the seed plants is overwhelmingly in the aerial reproductive structures; the pollen and seed embryos. Spatially and temporally, pollen and embryos are close ontogenetic derivatives of the angiosperm microspores and megaspores respectively. This suggests that the desiccation tolerance of pollen and embryos derives from the desiccation tolerance of the spores of antecedent taxa and that the basic pollen/embryo mechanism of desiccation tolerance has eventually become expressed also in the vegetative tissue of certain angiosperm species whose drought avoidance is inadequate in micro-habitats that suffer extremely xeric episodes. The protective compounds and processes that contribute to desiccation tolerance in angiosperms are found in the modern groups related to the evolutionary path leading to the angiosperms and are also present in the algae and in the cyanobacteria. The mechanism of desiccation tolerance in the angiosperms thus appears to have its origins in algal ancestors and possibly in the endosymbiotic cyanobacteria-related progenitor of chloroplasts and the bacteria-related progenitor of mitochondria. The mechanism may involve the regulation and timing of the accumulation of protective compounds and of other contributing substances and processes.

The evolution of desiccation tolerance in angiosperm plants: a rare yet common phenomenon

The present study examined the possibility of increasing the contents of some bioactive compounds of Spirulina platensis cultivated in medium containing various hydrogen peroxide concentrations (2, 4, 6 and 8 mM) as a model for environmental stress. A positive correlation was observed between the increase of H2O2 and increasing amounts of cellular lipophilic antioxidants (total carotenoids and α-tocopherol) and hydrophilic antioxidants [glutathione (GSH) and ascorbic acid (AsA)]. HPLC profile of carotenoids revealed that algae responded to the change of H2O2 exposure by the accumulation of higher amounts of β-carotene, astaxanthine, luteine, zeaxanthin and cryptoxanthin. S. platensis showed significant linear increase in activities of antioxidant enzymes, i.e., catalase (CAT), peroxidase (PX), ascorbate peroxidase (APX) and superoxide dismutase (SOD), with increasing H2O2 concentrations. A pronounced increase of oxidative lesions’ indexes [thiobarbituric acid reactive substances (TBARS) and paramagnetic radical-EPR signal] was found in algal grown at 8 mM H2O2. These data revealed that S. platensis behaved with different strategies against H2O2 exposure which is dose dependent and their response strongly correlated with the scavenging enzymes (SOD, CAT, PX and APX) and antioxidant compounds (GSH, AsA, β-carotene, astaxanthine and α-tocopherol) in the antioxidant defense systems. Therefore, S. platensis could be considered as good candidates for successful cultivation in artificial open ponds under different environmental conditions, as high value health foods, functional foods and as source of wide spectrum of nutrients.

Enhancement of antioxidant production in Spirulina platensis under oxidative stress

The purpose of this study was to illustrate the enhancing process of phenolics synthesis in Spirulina maxima grown in Zarrouk’s medium supplemented with different concentration of NaNO3 and/or combined with phenylalanine (L-PA). Also, the protective efficacy of Spirulina polyphenolic (SPP) extracts against CCI4-induced microsomal lipid peroxidation and scavenging of hydroxyl radical formation were performed. The results revealed that the levels of NaNO3 and L-PA in growth medium had positive effects on the production of biomass (34-64 mg/day), total phenolics (4.51-16.96 mg/g d.w) and flavonoids (1.32-5.12 mg/g d.w) contents. The highest levels of these compounds were obtained in Zarrouk’s medium containing 3.77 g/L NaNO3 and 100 mg/L L-PA. The HPLC-DAD profile of all phenolic extracts of Spirulina showed the presence of large numbers of phenolic acids and flavonoids, in variable levels. Gallic, chlorogenic, cinnamic, pinostrobin and p-OH-benzoic were found as the most abundant constituents among different extracts. Polyphenolic of Spirulina exhibited antioxidant effects  CCI4-induced lipid peroxidation (inhibition %) in liver homogenate and on DPPH radical scavenging activity (with IC50 values ranged from 23.22 to 35.62 ig/ml), in dose-depended manner. Their protective potential was comparable to that of standard phenolic antioxidants (BHT, BHA and -tocopherol, with IC50 values ranged from 13.22 to 23.62 ig/ml). Thus, S. maxima can be regarded as potent natural sources of nutraceutical and functional ingredients.

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F. K. El Baz

Papers

Enhancement of antioxidant production in Spirulina platensis under oxidative stress

Production of phenolic compounds from Spirulina maxima microalgae and its protective effects