Extracellular polymeric substances with high radical scavenging ability produced in outdoor cultivation of the thermotolerant chlorophyte Graesiella sp.

Wejdene Gongi,Nereida Cordeiro,Hatem Ben Ouada,Juan Luis Gomez Pinchetti,Saloua Sadok

doi:10.1007/s10811-020-02303-0

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.

Highlights

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
Graesiella sp. biomass and extracellular polymeric substances (EPSs) kinetics were evaluated by following the increase in biomass density and EPS concentration, of the batch cultures grown over 9 days under natural environmental conditions (Fig. 1)
In most microalgae and cyanobacteria species, EPSs are produced during the stationary growth phase (Delattre et al 2016)

Summary

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. 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. Among these resources, thermotolerant microalgae strains have exceptional potential. As a consequence of growth at high temperatures, thermotolerant microalgae can possess wide possibilities for physiological adaptation and genetic modifications that make them potential producers of high-value thermo-stable bioactive compounds (Haki and Rakshit 2003).

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