Abstract
Microalgal extracellular polymeric substances (EPSs) are heteropolysaccharides that have characteristics suitable for industrial and biotechnological applications. Notably, they have strong anionic nature and high hydrophobicity. Nevertheless, systematic studies to demonstrate the viability of the production of EPSs on an industrial scale are still crucial. In this research, the chlorophyte Graesiella was grown on a raceway pond to view its EPS valorization. The biomass production achieved a maximum of 1.98 g L−1 and an EPS production of 1.6 g L−1 after six production days. The Graesiella EPSs with a molecular weight above 100 kDa are sulfated exopolymers containing mainly polysaccharide (70%) and protein (16%). The EPSs produced more stable emulsions with hydrocarbons and oils than Tween-20. The emulsification indices with n-hexane (88%) and maize oil (28%) indicate the EPSs’ strong emulsion-stabilizing capacity. The EPSs showed a peak flocculating percentage of 95% to kaolin suspension, with better flocculation performance than Al2(SO4)3 and alginate. Moreover, Graesiella EPSs had a significant effect on antimicrobial activity, significantly inhibiting fungal growth (71% for Botytis cinerea and 87% for Fusarium oxysporum), spore germination (100% of inhibition at a concentration of 1.8 g L−1), and mycelium growth (68% of inhibition). Also, Graesiella EPSs acted as a bactericide against Vibrio anguilaruim and Listonella anguilaruim (100% inhibition). EPSs were also found to have potent antioxidant activity compared with l-ascorbic acid. The obtained results open new perspectives to the further exploration of Graesiella sp. as a potential EPS producer, making it a promising candidate for numerous industrial applications.
Highlights
International demand for polymers continues to climb as the world population increases
1,1-Diphenyl-2-picrylhydrazyl free radical (DPPH) scavenging activity The DPPH scavenging activity was studied as described by Shimada et al (2002), with slight modifications
The absorbance was measured at 517 nm (Asample) and normalized to a blank sample consisting of DPPH solution (Acontrol)
Summary
International demand for polymers continues to climb as the world population increases. Amidst the increasing worry regarding harmful environmental damage and exhaustible fossil resources, there is significant interest in using natural resources for polymeric materials (Hillmyer 2017; Hong and Chen 2017). Various sustainable polymers extracted from macroalgae (agar, carrageenan, and alginate) and bacteria (dextran and xanthan gum) have been found to have biodegradability, biocompatibility, thermo-stability, and even biological activities (Brunchi et al 2016; Martău et al 2019; Wang et al 2020). These properties have targeted applications in the packaging, agricultural, textile, pharmaceutical, and medical domains (Nwodo et al 2012). Biopolymers extracted from macroalgae and bacteria are obtained following chemical or enzymatic
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