Sulfated Galactans from Agarophytes: Review of Extraction Methods, Structural Features, and Biological Activities

Abstract

Agarophytes are important seaweeds of the Rhodophyta type, which have been highly exploited for industrial use as sources of a widely consumed polysaccharide of agar. In addition to that, sulfated galactans (SGs) from agarophytes, which consist of various functional sulfate groups, have attracted the attention of scientists in current studies. SGs possess various biological activities, such as anti-tumor, anticoagulant, anti-inflammatory, antioxidant, anti-obesity, anti-diabetic, anti-microbial, anti-diarrhea, and gut microbiota regulation properties. Meanwhile, the taxonomy, ecological factors, i.e., environmental factors, and harvest period, as well as preparation methods, i.e., the pretreatment, extraction, and purification conditions, have been found to influence the chemical compositions and fine structures of SGs, which have, further, been shown to have an impact on their biological activities. However, the gaps in the knowledge of the properties of SGs due to the above complex factors have hindered their industrial application. The aim of this paper is to collect and systematically review the scientific evidence about SGs and, thus, to pave the way for broader and otherwise valuable industrial applications of agarophytes for human enterprise. In the future, this harvested biomass could be sustainably used not only as a source of agar production but also as natural materials in functional food and pharmaceutical industries.

Keywords: agarophytes; bioactivity; extraction; structure; sulfated galactans.

Figure 1

Statistical analysis of published papers and patents related to SGs within the past 20 years. (A) Annual publication. (B) Research areas.

Figure 2

The procedure and methods of pretreatment, extraction, and purification of sulfated galactans.

Figure 3

Schematic representation of sulfated galactans from red seaweed, Gracilaria spp. [45,95].

Figure 4

Schematic representation of sulfated galactans from red seaweed, Porphyra spp. [64].

Figure 5

Schematic representation of sulfated galactans from red seaweed, Gelidium spp. [15,103].

Figure 6

Schematic representation of sulfated galactans from red seaweed, Ahnfeltia spp. [16].

Figure 7

Overview of related bioactivities of anti-inflammatory and anti-lipid of SGs from seaweed of agarophytes. Sulfated galactans (SGs) express the main potential to decrease malondialdehyde (MDA) levels in liver, which affects the capacity of lipid metabolism and the release of pro-inflammatory mediators such as cytokines and chemokines, including autacoids. When MDA level is decreased, the liver is alleviated from injury from improper lipid and inhibits lipid oxidation. SG treatment shows improvements by these mechanisms in the induced rats model.