Valorization of Seaweed Carbohydrates: Autohydrolysis as a Selective and Sustainable Pretreatment

Abstract

Seaweeds are promising feedstocks; nevertheless, the lack of systematic approaches to recover different high-value fractions in a clean and sustainable mode hampers their exploitation. Due to this necessity, an innovative environmentally friendly strategy was proposed in this article for the development of a sugar platform from Gelidium sesquipedale: for the first time, autohydrolysis followed by enzymatic saccharification (with cellulolytic and agarolytic cocktails) was applied to agarophyte seaweeds. The wide range of severities (between 2.47 and 4.94) studied in this work proved that the autohydrolysis-based process can be tuned to selectively extract different target carbohydrate fractions. Gelling agents (reaching 30 g/100 g DW) can be obtained by the application of low severity treatments, fermentable sugars or oligosaccharides with the nutraceutical potential (reaching 14 g/100 g DW) are produced when severity is increased, and at the highest severity, platform chemicals (reaching 4 g/100 g DW) are the final product. The reduction of processing times compared to traditional extraction methodologies and the elimination of chemicals used in dilute acid treatments make this strategy a clean and sustainable alternative for the valorization of both glucan and galactan fractions of G. sesquipedale.

Advances in Extraction Methods to Recover Added-Value Compounds from Seaweeds: Sustainability and Functionality

“…Moreover, the obtained products had important bioactivities suitable for cosmetic, nutraceutical and pharmaceutical industries [ 28 , 61 , 73 ]. For instance, significant antihypertensive activity has been described for hydrolyzed peptides from red seaweeds [ 86 , 87 ]. EAE extraction applied on Sargassum muticum , Osmundea pinnatifida , and Codium tomentosum presented the highest nitrogen and total phenolics contents, highest sulfated polysaccharide contents and highest prebiotic activity, respectively.…”

“…SWE applied by Trigueros [ 82 ] on protein fractions of Gelidium sesquipedale residues showed to be efficient and the work highlighted that the non-polar selectivity is directly proportional to the severity factors of the extraction method. Furthermore, Gomes et al [ 87 ] were able to extract different polysaccharide fractions from red seaweeds with different functionalities depending on the severity factor applied. Medium severity factors allowed to extract structural polysaccharides (agar), without impairing its gelling ability, while harsher severities hydrolyzed the polysaccharides available into oligosaccharides (eventually with prebiotic activity) or monosaccharides that could be used as substrate to fermentative processes.…”

“…The color removal (both phycobilliproteins and ethanol soluble pigments) prior to the carbohydrates will allow to valorize these fractions (without thermal degradation) while bleaching and facilitating the subsequent steps. Thermal extraction of carbohydrates can be made either by OH or by PSE with water as solvent [ 87 ], allowing energetic advantages and/or tuning for the desired carbohydrate product. Further protein recovery can be made through chemical processes, but also using EAE with proteases and finally the residual biomass can be converted to a glucose rich fraction to be used as fermentation substrate by autohydrolysis (that can be viewed as a particular case of sub-critical water extraction), using high severity factors.…”

The Red Seaweed Giant Gelidium (Gelidium corneum) for New Bio-Based Materials in a Circular Economy Framework

“…Gelidium corneum is known to have a high content of polysaccharides, very low content of lipids, and a fairly high content of protein [180,181]. Further, a close analysis of G. corneum shows that there are significant seasonal variations in the moisture, ash, protein, lipid, and carbohydrate content of the harvested wild biomass [6].…”

Adjustable Gel Texture of Recovered Crude Agar Induced by Pressurized Hot Water Treatment of Gelidium sesquipedale Industry Waste Stream: An RSM Analysis

“…In the same trend, the industrial extraction of agar has progressed considerably from a simple freezing process in the 1920s to more modern techniques. Microwave-assisted extraction [ 9 ], autoclave extraction, accelerated solvent extraction, ultrasounds coupled with hot water extraction [ 10 ], and enzyme-assisted extraction [ 11 ] are among the emerging technologies employed. According to Barrio et al [ 12 ], ultrasound tended to shorten the extraction time and allow for a higher agar extraction yield.…”