Biological valorization of co-products of agar extraction from Gelidium sesquipedale

L’objectif de ce travail est la valorisation des molécules bioactives présentes initialement dans Gelidium sesquipedale. Les rhodophycées agarophytes dont Gelidium sesquipedale sont exploitées à l’échelle industrielle pour l’agar, un phycocolloïde aux propriétés gélifiantes, qu’elles contiennent en abondance. Une multitude de coproduits sont générés lors de l’extraction de l’agar. Ces derniers, peu étudiés, ne sont pas valorisés alors qu’ils constituent une source potentielle de molécules d’intérêts. En premier lieu, le process industriel d’extraction de l’agar a été adapté à l’échelle du laboratoire afin de récupérer ces co-produits dont l’analyse a montré la richesse en glucides. Ils ont par la suite été fractionnés pour isoler les oligosaccharides dont certains sont connus comme éliciteurs chez les plantes. Ainsi, plusieurs fractions oligosaccharidiques ont été obtenues avec un rendement estimé à 15,7% de Gelidium sesquipedale sec. Les fractions sélectionnées ont été caractérisées par CPG, ESI-MS, RMN et perméthylation ce qui a permis d’élucider les structures des oligosaccharides qu’elles contiennent et de révéler notamment la présence de dérivés de floridoside dont le Gal2glycérol, le Gal3glycérol et le Gal4glycérol qui sont des molécules originales chez Gelidium sesquipedale non décrites à ce jour chez les algues rouges. Une dernière partie a consisté en la mesure de l’activité élicitrice de ces fractions qui a pu être vérifiée sur des plantes de tomate à travers des mesures de marqueurs biochimiques relatifs à l’expression des réactions de défense chez la plante. En conclusion, les coproduits issus de l’extraction de l’agar représentent une source de pSDNs (phyto stimulateur des défenses naturelles chez la plante) ; ils offrent une nouvelle perspective de développement à l’industrie de l’agar.This work aims at promoting the bioactive molecules initially present in Gelidium sesquipedale. The rhodophycea agarophytes, including Gelidium sesquipedale, are used for industrial extraction of agar, a phycocolloid with gelling properties, which they contain in abundance. A multitude of co-products are generated during the extraction of the agar. These co-products have only been studied a little, hence not valued, while they constitute a significant source of molecules of interest. Firstly, the industrial agar extraction process was adapted on a laboratory scale, in order to recover these coproducts, which were subsequently subjected to an analysis, which revealed the presence of carbohydrates as major components. They were submitted to a fractionation process to obtain oligosaccharidic fractions, with a potential of elicitor activity, and a yield estimated at 15.7% of dry Gelidium sesquipedale. Also, a follow-up of co-products from batches of Gelidium sesquipedale harvested in different years from 2014 to 2016, enabled the comparison of the composition of the various co-products, depending on the year of the harvest, and thus to evaluate the variability of the initial resource. In addition, the impact of an extraction factor, being the sodium concentration, and the comparison with an industrial co-product produced by this process, were carried out. The retained fractions were characterized by GPC, ESI-MS, NMR and permethylation that allowed the elucidation of the structures of the oligosaccharides they contain, and revealed in particular the presence of floridoside derivatives including Gal2glycerol, Gal3glycerol and Gal4glycerol, which are original molecules in Gelidium sesquipedale, not described to date in red algae. A final part consisted in measuring the activity of these fractions as elicitor that could be estimated on tomato plants through measurements of biochemical markers relating to the expression of defense reactions in the plant. In conclusion, the co-products from agar extraction represent a source of pSDNs (phyto stimulator of natural defense in the plant) and give a new perspective to the agar industry

Assessment of the Red Seaweed Gelidium sesquipedale By-Products as an Organic Fertilizer and Soil Amendment

The agar extraction process of the red algae Gelidium sesquipedale generates a solid residue as the main by-product. However, this residue remains non-valorized, despite its potential as a fertilizer. This study aims to determine the value of G. sesquipedale residue as organic fertilizer and for soil amendments. An incubation test of G. sesquipedale residue in soils was performed to measure the nitrogen (N), phosphorus (P), and calcium (Ca) release. The potential fertilization effect of the residue was evaluated in a greenhouse on two crops: strawberry and corn. The amount of available P was high at the beginning of the incubation experiment. The amounts of nitrate–nitrogen (NO₃−-N) and available Ca increased over the incubation time. A high efficiency of fertilization using the residue at different concentrations was observed in both crops. Application of the residue enhanced crop growth. The fertilization effect was associated with increased macro- and micro-elements in the strawberry fruit’s N, Ca, iron (Fe), manganese (Mn), and zinc (Zn) and in the corn leaves’ N, P, magnesium (Mg), and Fe. Moreover, the residue was a good soil organic amendment as it enhanced the amount of organic matter (OM) and some macro- and micro-elements in the soil after plant harvest

Assessment of the Red Seaweed <i>Gelidium sesquipedale</i> By-Products as an Organic Fertilizer and Soil Amendment

The agar extraction process of the red algae Gelidium sesquipedale generates a solid residue as the main by-product. However, this residue remains non-valorized, despite its potential as a fertilizer. This study aims to determine the value of G. sesquipedale residue as organic fertilizer and for soil amendments. An incubation test of G. sesquipedale residue in soils was performed to measure the nitrogen (N), phosphorus (P), and calcium (Ca) release. The potential fertilization effect of the residue was evaluated in a greenhouse on two crops: strawberry and corn. The amount of available P was high at the beginning of the incubation experiment. The amounts of nitrate–nitrogen (NO₃−-N) and available Ca increased over the incubation time. A high efficiency of fertilization using the residue at different concentrations was observed in both crops. Application of the residue enhanced crop growth. The fertilization effect was associated with increased macro- and micro-elements in the strawberry fruit’s N, Ca, iron (Fe), manganese (Mn), and zinc (Zn) and in the corn leaves’ N, P, magnesium (Mg), and Fe. Moreover, the residue was a good soil organic amendment as it enhanced the amount of organic matter (OM) and some macro- and micro-elements in the soil after plant harvest

Agar extraction by-products from gelidium sesquipedale as a source of glycerol-galactosides

International audienceAlkaline treatment is a common step largely used in the industrial extraction of agar, a phycocolloid obtained from red algae such as Gelidium sesquipedale. The subsequent residue constitutes a poorly valorized by-product. The present study aimed to identify low-molecular-weight compounds in this alkaline waste. A fractionation process was designed in order to obtain the oligosaccharidic fraction from which several glycerol-galactosides were isolated. A combination of electrospray ion (ESI)-mass spectrometry, H-1-NMR spectroscopy, and glycosidic linkage analyses by GC-MS allowed the identification of floridoside, corresponding to Gal-glycerol, along with oligogalactosides, i.e., (Gal)(2-4)-glycerol, among which -d-galactopyranosyl-(13)--d-galactopyranosyl1-2-glycerol and -d-galactopyranosyl-(14)--d-galactopyranosyl1-2-glycerol were described for the first time in red algae