ISSUE FOCUS FEED & ADDITIVE MAGAZINE November 2022 49 compounds with potential applications in human and animal nutrition. Their biochemistry includes polysaccharides, peptides, essential fatty acids, phlorophenols, phytogens, pigments and minerals. Among the bioactive compounds in seaweed, the polysaccharides are of particular interest for their specific prebiotic effect on the gastrointestinal (GI) microbiota and reported health and nutrition benefits (Sardari and Karlsson, 2018; Cherry et al., 2019; Shannon et al., 2021). SEAWEED POLYSACCHARIDES Unique polysaccharides (dietary fibre) found only in seaweed account for around 30-75% of dry weight, serving a structural role in cell walls (Xu et al, 2017). Of the total fibre in seaweed, a proportion is soluble polysaccharides, possessing particular prebiotic activity. The soluble polysaccharides generally comprise around 55–65% of total fibre in commonly used green and red seaweed and can be even higher in commonly used brown seaweed (Lahaye 1991). These soluble polysaccharides are particularly effective prebiotics in animals (Hentati et al, 2020). Relative to fibres in land-based plants, seaweed polysaccharides tend to be more highly substituted, more complex and less lignified, making them attractive as functional prebiotics in the animal hindgut. In addition to solubility as a functional property, the sulphated seaweed polysaccharides are unique in that they combine the bioactivities of polysaccharides and the attached sulphate group. The fibres identified in 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 and agars, the predominant polysaccharides in brown and red seaweed, respectively, are not. 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 or land plant polysaccharide 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 and structural and conformation characteristics (Hentati et al., 2020). Numerous scientific papers indicate that seaweed polysaccharides may display bioactive properties including anticoagulant, antioxidant, antithrombotic, bacteriostatic and antiviral activities. Several studies have reported that sulphated polysaccharides extracted from different seaweeds have demonstrated an inhibitory effect on the growth of pathogenic bacteria (De Jesus Raposo et al 2015). Extracts rich in seaweed fibres decreased the faecal E. coli populations in pigs and reduced bacterial load in raw meat products (McDonnel et al, 2010). Furthermore, green seaweed polysaccharides such as ulvans have been shown to possess strong immune-modulating activities (Wany et al., 2014). However, evidence suggests the prebiotic effect is the primary mode of action by which macroalgal polysaccharides added to animal feed influences GI microbial profile, physiological indicators of GI health, digestive efficiency and growth response in animals. Figure 1: Relative abundance of caecal bacteria at phylum level in broiler chickens consuming control diets or with added OceanFeedTM Poultry seaweed blend for 42 days.
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