Algal Research 80 (2024) 103542 Available online 9 May 2024 2211-9264/© 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies. Compositional, structural, and functional characterization of fucoidan extracted from Sargassum polycystum collected from Saint Martin’s Island, Bangladesh Dipak Roy a , Mohammad Khairul Alam Sobuj b , Md. Shoebul Islam c , Md. Mozammel Haque a , Md. Ariful Islam a , Md. Mohidul Islam b , Md. Zulfikar Ali d , S.M. Rafiquzzaman a, * a Department of Fisheries Biology and Aquatic Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh b Marine Fisheries and Technology Station, Bangladesh Fisheries Research Institute, Cox’s Bazar 4700, Bangladesh c Shrimp Research Station, Bangladesh Fisheries Research Institute, Bagerhat 9300, Bangladesh d Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh A R T I C L E INFO Keywords: Fucoidan Sargassum polycystum Extraction Composition Antioxidant Antidiabetic ABSTRACT Fucoidan is a sulphated polysaccharide with diversified biological activities commonly found in brown seaweeds. In our present study, fucoidan was extracted from Sargassum polycystum collected from Saint Martin’s Island in three different extraction methods. The composition of the fucoidans was determined by measuring the total carbohydrate, sulfate, uronic acid, fucose, and protein contents. Fourier-transform infrared spectroscopy (FT-IR) and Proton nuclear magnetic resonance ( 1 H NMR) were studied to determine the structural groups of extracted fucoidans. Functional activities were analyzed by antioxidant activity and anti-diabetic activity assay. Fucoidan yield was obtained highest in the acid extraction method (0.061 ± 0.007 g/g), followed by the water extraction method (0.058 ± 0.005 g/g) and salt extraction method (0.041 ± 0.005 g/g). Water extracted fucoidan showed the highest carbohydrate content (62.97 %), uronic acid content (6.46 %), and protein content (2.62 %). Sul- phate content (28.56 %) was highest in salt extracted fucoidan, whereas fucose content (24.0 %) was highest in water extracted fucoidan. FT-IR and 1 H NMR analysis confirm several characteristic picks for the extracted fucoidans. Extracted fucoidans presented comparable antioxidant activity, but salt-extracted fucoidan presented the highest DPPH radical scavenging assay (86.85 ± 0.74 %, IC 50 = 0.03 mg/mL), ABTS radical scavenging assay (65.13 ± 0.92 %, IC 50 = 1.94 mg/mL), Phosphomolybdenum assay (4.356 ± 0.11) and Nitric Oxide (NO) radical scavenging assay (57.08 ± 0.52 %, IC 50 = 3.73 mg/mL) in dose-dependency manner. Further anti-diabetic ac- tivity assay resulted in the highest α-amylase inhibition activity (62.82 ± 1.36 %, IC 50 = 2.30 mg/mL) and α-glucosidase inhibition activity (55.73 ± 0.84 %, IC 50 = 3.71 mg/mL) by salt-extracted fucoidan. These func- tional potentials of seaweed may add significant value to the development of functional food and pharmaceutical materials. 1. Introduction Fucoidans are intricate and diverse natural sulphated poly- saccharides frequently encountered in brown seaweeds’ cell walls and several invertebrate species, such as the sea cucumber and sea urchin. The structural and compositional features of brown seaweeds exhibit variation, characterized mainly by the presence of fucose and sulphate, accompanied by minor quantities of galactose, xylose, mannose, and uronic acids [1]. Sulphate groups constitute a significant proportion of fucoidan, and the biological properties of fucoidan are closely associated with its sulphate content [2]. The structure of fucoidan is still a mystery due to its lack of confined regularity and its various components despite extensive investigations into its structural features [3]. It was found that fucoidans exhibited a diverse range of commendable biological activ- ities, including antioxidant, anti-inflammatory, anti-allergic, anti- tumor, anti-obesity, anti-coagulant, anti-viral, anti-hepatopathy, anti- uropathy, and anti-renalpathy effects [4]. Furthermore, the isolated fucoidan revealed significant anti-proliferative properties and * Corresponding author. E-mail addresses: dipakroy429@gmail.com (D. Roy), khairulsobuj6@gmail.com (M.K.A. Sobuj), shoebulshopnil@gmail.com (Md.S. Islam), mdmhaque1997@ gmail.com (Md.M. Haque), aiashir77@gmail.com (Md.A. Islam), mohidbfri@gmail.com (Md.M. Islam), rafiquzzaman@bsmrau.edu.bd (S.M. Rafiquzzaman). Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal https://doi.org/10.1016/j.algal.2024.103542 Received 3 November 2023; Received in revised form 20 March 2024; Accepted 8 May 2024