Brown algae (Phaeophyceae) have been consumed by humans for hundreds of years. Current studies have shown that brown algae are rich sources of bioactive compounds with excellent nutritional value, and are considered functional foods with health benefits. Polysaccharides are the main constituents of brown algae; their diverse structures allow many unique physical and chemical properties that help to moderate a wide range of biological activities, including immunomodulation, antibacterial, antioxidant, prebiotic, antihypertensive, antidiabetic, antitumor, and anticoagulant activities. In this review, we focus on the major polysaccharide components in brown algae: the alginate, laminarin, and fucoidan. We explore how their structure leads to their health benefits, and their application prospects in functional foods and pharmaceuticals. Finally, we summarize the latest developments in applied research on brown algae polysaccharides.

Lytic polysaccharide monooxygenase (LPMOs) are enzymes that catalyze the breakdown of polysaccharides in biomass and have excellent potential for biorefinery applications. However, their activities are relatively low, and methods to measure these activities are costly, tedious or often reflect only an apparent activity to the polysaccharide substrates. Here, we describe a new method we have developed that is simple to use to determine the activities of type-1 (C1-oxidizing) LPMOs. The method is based on quantifying the ionic binding of cations to carboxyl groups formed by the action of type-1 LPMOs on polysaccharides. It allows comparisons to be made of activities under different conditions. Based on the colorimetric detection and quantification of the pyrocatechol violet (PV)-Ni²⁺ complex, we have developed an assay to reliably detect and quantify carboxylate moieties introduced by type-1 LPMOs. Conditions were optimized for determining the activities of specific LPMOs. Comparisons were made of the activities against cellulose and chitin of a novel AA10 LPMO and a recently reported family AA11 LPMO. Activities of both LPMOs were boosted by hydrogen peroxide in the 1st hour of the reaction, with a 16-fold increase for the family AA11 LPMO, and up to a 34-fold increase for the family AA10 LPMO. We developed a versatile colorimetric cation-based assay to determine the activities of type-1 LPMOs. The assay is quick, low cost and could be adapted for use in industrial biorefineries.

The gene CCT67099 from Fusarium fujikuroi was shown to encode a novel enzyme from the Lytic Polysaccharide Monooxygenase (LPMO) Family AA11. The gene was expressed and a truncated version of the enzyme, designated as FfAA11, was purified from the periplasmic space of Escherichia coli cells at high yield. FfAA11 exhibited oxidative activity against α- and β-chitins, as well as lobster shells. Under optimised conditions, FfAA11 introduced 35 nmol of carboxylate (COO⁻) moieties per milligram of α-chitin. These carboxylate groups were introduced onto the chitin surface under mild enzymatic oxidation conditions in an aqueous solution without changes to the crystallinity of the chitin fibres. FfAA11 was also combined with a simple and environmentally friendly chemical method that transforms recalcitrant chitins into desirable functionalised (nano)materials. The use of ethyl(hydroxyimino)cyanoacetate (Oxyma)-assisted click chemistry allowed the rapid modification of the surface of FfAA11-oxidized chitins, with a fluorescent probe, a peptide, and gold nanoparticles. The chemical steps performed, including the FfAA11 oxidase treatment and surface chemical modification, were achieved without the production of any toxic by-products or waste organic solvents. This approach represents a novel method for the greener production of chitin-based biomaterials.

D-mannose is a natural and biologically active monosaccharide. It is the C-2 epimer of glucose and a component of a variety of polysaccharides in plants. In addition, D-mannose also naturally exists in some cells of the human body and participates in the immune regulation of cells as a prebiotic. Its good physiological benefits to human health and wide application in the food and pharmaceutical industries have attracted widespread attention. Therefore, in-depth research on preparation methods of D-mannose has been widely developed. This article summarizes the main production methods of D-mannose in recent years, especially the in-depth excavation from biomass raw materials such as coffee grounds, konjac flour, acai berry, etc., to provide new ideas for the green manufacture of D-mannose.