Physico-chemical characterization and enzymatic functionalization of Enteromorpha sp. cellulose

Highlights

• Green macro algae cellulose was extracted to investigate its physic chemical properties.

• Enteromorpha sp. cellulose was highly amorphous and presented interesting rheological properties.

• Algae cellulose could be enzymatically functionalized to reducing sugars or biosurfactants.

Abstract

Although green macro-algae represent a renewable and highly abundant biomass, they remain poorly exploited in terms of carbohydrate polymers compared to red and brown ones and other lignocellulosic materials. In this study, cellulose from the green macro-algae Enteromorpha sp. was isolated, physico-chemically characterized and enzymatically functionalized. The cellulose content was about 21.4% (w/w). FTIR analyses indicated an absence of acetyl or uronic esters confirming the absence of hemicellulose contamination. The 36% crystallinity index of the extracted cellulose revealed a high amorphous character as determined by X-ray diffraction. The moisture adsorption isotherms and specific surface measurements were respectively 42.87 g/100 g and 8.34 m²/g. The Enteromorpha sp. cellulose was first enzymatically saccharified by a commercial cellulase preparation from Aspergillus niger with a hydrolysis yield of 70.4%. Besides, it was successfully functionalized based on the transglycosylation mechanism of the same enzymatic preparation, to produce highly added-value biosurfactants (butyl-glucoside) with a concentration of 8 mM.

Introduction

Different biomasses such as agricultural products, marine seaweed or woody materials are produced in huge amounts annually. These different biomasses sources are exploited for different applications such as biofuel production, enzymes, bio surfactants etc. (Pandey, Soccol, Nigam, & Soccol, 2000).

An increasing interest is given to algal biomass for different reasons. It is mainly characterized by a sustainable growth, coupled with the facility of cultivation outdoor in aquatic media such as photobioreactors or open basins. Additionally, the use of algae doesn’t affect any human food sources (Goh & Lee, 2010; Lee et al., 2011a). These main advantages make algal biomass in effect an important material for different industrial applications. Macroalgae are classified in, brown, green and red algae. They live principally on coastal rocks and shallow seas (Lee, Ahn, Hwangm, & Lee, 2011b). Green algae represent in fact the most important available biomass that proliferates mainly in coastal waters (Robic et al., 2009a, Robic et al., 2009b).

The main exploited compounds from algae are phycocolloids from red and brown ones, namely carrageenan, alginate and agar, which represent the major fraction (Gunay & Linhardt, 1999). These polysaccharides are applied in a wide range of industries such as cosmetic, food and pharmaceutical (Feng, Liu, Li, Peng, & Song, 2011). Unlikely, green macroalgae are poorly exploited due to their special composition. They have the particularity to contain a sulfated matricial polysaccharide known as ulvan (Robic, Gaillard, Sassi, Lerat, & Lahaye, 2009c). Their cell wall polysaccharides form however 38–54% of the dry weight (Lahaye & Kaeffer, 1997).

Green macroalgae are considered as opportunistic organisms. They proliferate in biotic or abiotic conditions (Hayden et al., 2003, Lotze and Worm, 2002). Due to the anthropologic activities, the eutrophication level increased significantly in sea water and algae green tides became more frequent, generating many health and environmental problems (Hauxwell, Cebrián, Furlong, & Valiela, 2001).

Hence, exploiting green macroalgae will have a considerable interest in the environmental and biotechnological fields. Precisely, this abundant resource represents an interesting substrate for bio refinery or for the production of highly added-value molecules (Lin, Zhu, Xu, Liu, & Jia, 2009).

For the green macroalgae, the main characterized polysaccharide was ulvan (Robic et al., 2009a, Robic et al., 2009b, Robic et al., 2009c). However, few studies have focused on the parietal cell-wall polysaccharides like cellulose. Thus, this work aimed at the evaluation of the content, the quality, the spectroscopic and rheological properties, and the enzymatic conversion potentiality of cellulose from the green macroalgae Enteromorpha sp. An innovative strategy for the production of highly added-value butyl-glucoside (biosurfactant) is then proposed.