ISSUE FOCUS 28 FEED & ADDITIVE MAGAZINE May 2022 The numerous seaweeds identified contain varying amounts of fibre, consisting mainly of polysaccharides, with only small amounts of disaccharides and monosaccharides. Seaweed polysaccharides primarily occur in sulphated and non-sulphated forms. The structural array of polysaccharides functions as either matrix or storage molecules that differ in composition between seaweed species (Figure 2). In addition to solubility as a functional property, sulphated polysaccharides (SP) of seaweed origin are unique in that they combine the bioactivities of polysaccharides with the additional bioactivity of the attached sulphate group (Hentati et al, 2020). These SPs identified in brown, green and red seaweed are generally absent in land-based plants (Berri et al, 2017). The extent to which seaweed polysaccharides are sulphated differs among the main seaweed species. For example, the ulvans from green algae are extensively sulphated, whereas alginates, the predominant polysaccharide in brown seaweed, are not sulphated. The high diversity in seaweed polysaccharides provides opportunities to combine different seaweed species, creating a more diverse source of prebiotic fibres compared to using a single seaweed as a source of prebiotic fibre. This concept has been used to formulate specific blends of seaweeds, containing varying proportions of brown, green and red seaweeds. The bioactivity of seaweed polysaccharides depends on factors such as molecular weight, charge density, sulphate content of sulphated polysaccharides and structural and conformation characteristics (Hentati et al., 2020). Numerous scientific research reports indicate seaweed polysaccharides may display several bioactive properties including anticoagulant, antioxidant, antitrombotic, bacteriostatic and antiviral activities. However, evidence suggests, the prebiotic effect is the primary mode of action by which seaweed polysaccharides, added to animal feed influences GI microbial profile, physiological indicators of GI health, digestive efficiency and growth response in animals. PREBIOTIC EFFECTS OF SEAWEED POLYSACCHARIDES IN ANIMALS The prebiotic effect of seaweed polysaccharides in animals has been investigated under in vitro and in vivo conditions. While early studies were helpful in demonstrating the prebiotic properties of seaweed polysaccharides, the information provided is incomplete due to the lack of adequate techniques for assessing changes in the GI microbiota. However, reFigure 2: The polysaccharides in brown, green and red seaweeds (from Stiger and Deslandes, 2016).
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