Extracellular polymeric substances with high radical scavenging ability produced in outdoor cultivation of the thermotol
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Extracellular polymeric substances with high radical scavenging ability produced in outdoor cultivation of the thermotolerant chlorophyte Graesiella sp. Wejdene Gongi 1,2 & Nereida Cordeiro 3,4 & Juan Luis Gomez Pinchetti 5 & Saloua Sadok 1 & Hatem Ben Ouada 1 Received: 16 June 2020 / Revised and accepted: 12 October 2020 # Springer Nature B.V. 2020
Abstract The present study developed a two-step strategy to enhance the production of extracellular polymeric substances (EPSs) by a thermotolerant chlorophyte, Graesiella sp., in view to their industrial valorisation. In the first step, Graesiella sp. was grown in outdoor conditions in pilot-scale photobioreactors of 100 L culture volumes. In the second step, the biomass collected in the exponential growth phase was submitted to heat stress (50 °C). A joint production of biomass reaching 0.50 gdw L−1 day−1 and of EPS production reaching 1.30 gdw L−1 in 2 days was obtained. EPSs mainly contained polysaccharides (80%) and proteins (14%). FTIR and 1HNMR revealed the presence of primary amine and sulfated groups. The EPSs contained antioxidant enzymes (SOD, CAT, and APX) maintained in an active state by the microenvironment offered by the EPSs. The EPSs were found to have a potent antioxidant activity via directly scavenging free radicals when compared to L-ascorbic acid. Keywords Microalgae . Graesiella . Chlorophyta . EPSs . Antioxidant enzymes . Characterization . Radical scavenging . Outdoor cultivation . Two-step strategy
Introduction In various sectors such as food, cosmetic, and health, the market is growing rapidly in the support of the development of “bio” products and in a global context of demand for reduction of chemical additives. Recently, it has been shown that the microalgae field has significant potential (Vigani et al. 2015) supporting the transition from a fossil fuel-based economy and the global mass-market industry to a “circular
* Hatem Ben Ouada [email protected] 1
Laboratory of Blue Biotechnology & Aquatic Bioproducts, National Institute of Marine Sciences and Technologies, 5000 Monastir, Tunisia
2
National Institute of Agronomy, University of Carthage, 1082 Tunis, Tunisia
3
LB3 Faculty of Science and Engineering, University of Madeira, 9000-390 Funchal, Portugal
4
CIIMAR, Interdisciplinary Centre of Marine and Environmental Research, University of Porto, 4450-208 Matosinhos, Portugal
5
Spanish Bank of Algae, Institute of Oceanography and Global Change (IOCAG), University of Las Palmas de G.C, Muelle de Taliarte s/n, 35214 Telde, Canary Islands, Spain
bioeconomy” responding to a growing demand of civil society. Although the total production volumes and market size of products derived from microalgae increased 5-fold since the beginning of the century, they are still relatively small and little diversified with respect to alternative sources (Enzing et al. 2014). In this context, the mobilization of new microalgal resources with the versatility of applications (human and animal food and bioactives) would make original contributions t
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