Seaweed polysaccharides as a source of highly effective prebiotic fibre

Among the bioactive compounds highlighted in seaweed, the polysaccharides are of particular interest for their specific prebiotic effect on the gastrointestinal (GI) microbiota. This review provides a brief discussion on the prebiotic effect of seaweed polysaccharides on the GI microbiota. Specific examples of the prebiotic effects of seaweed polysaccharides, when applied as whole seaweed powder on the GI microbiota and the subsequent impacts on the animals are provided.

Dr Jason Sands
Head of Nutrition
Ocean Harvest Technology

Marine macroalgae (referred to as seaweed) consist of three diverse Phyla, the Phaeophyta (brown) Chlorophyta (green) and Rodophyta (red) seaweeds. Of the more than 10,000 species identified, a little under 300 species are commonly used globally. These can be further categorized into approximately, 163 species of Rhodophyceae, 75 of Pheophyceae and 33 of Chlorophyceae (White and Wilson, 2015). Numerous published reports and decades of successful use have highlighted the potential of seaweeds as rich sources of bioactive compounds with potential applications in animal nutrition. The range of bioactive components in seaweed include polysaccharides, peptides, essential fatty acids, polypnols, phytogens, pigments and minerals. Among the bioactive compounds highlighted in seaweed, the polysaccharides are of particular interest for their specific prebiotic effect on the gastrointestinal (GI) microbiota (de Jesus Raposo et al 2016; Sardari and Karlsson, 2018; Cherry et al., 2019; Shannon et al., 2021). This review provides a brief discussion on the prebiotic effect of seaweed polysaccharides on the GI microbiota. Specific examples of the prebiotic effects of seaweed polysaccharides, when applied as whole seaweed powder on the GI microbiota and the subsequent impacts on the animals are provided.

PREBIOTICS AND THE GI MICROBIOTA
Prebiotics are defined as non-digested food components that, through the stimulation of growth and/or activity of a single type or category of GI microbe, improve the health status of the host animal (Gibson and Roberfroid, 2017). To be considered a prebiotic a food component must: 1) be resistance to gastric acidity and hydrolysis by mammalian enzymes and subsequent gastrointestinal absorption; 2) be subject to fermentation by intestinal microflora; and 3) selectively stimulate the growth and/or activity of the intestinal bacteria that contribute to health and well-being of the host.

The gastrointestinal (GI) microbiota has been shown to affect the availability of nutrients in the intestine, modulate the immune response and to provide signals that effect behaviour of the host animal (Maslowski and Mackey, 2011; Stanley et al, 2014; LaBlanc et al 2017; Mesa et al, 2017). In healthy animals consuming a nutrient adequate diet, the microbial community has a specific composition (Borda-Molina et al, 2018; Tröscher-Mußotter et al, 2019). Poor diet, stress, infection, or other environmental challenges can alter the normal profile of the GI microbiota resulting in the development of a condition referred to as dysbiosis, a disturbance of the normal GI microbiota profile resulting in an altered immune response and consequent digestive disorders (DeGruttola et al, 2016).

Recent advances in genomic techniques have shed new light on the prebiotic effect of seaweed polysaccharides on the GI microbiota profile and related physiological effects (Borda Molina et al, 2018; Tröscher-Mußotter et al, 2019). Using metagenomic analyses, chicken cecal samples were found to contain Proteobacteria as the most abundant phylum (47–79%) followed by Firmicutes (12–28%) and Bacteroidetes (7–27%). At the family level, the Ruminococcaceae, Lachnospiraceae, Clostridiaceae, Eubacteriaceae and Unclassified bacteria are the more abundant species in the chicken ceca (Borda Molina et al, 2018). The dominant phyla in the pig’s cecaum are the Firmicutes and Bacteroidetes, which account for mor ethan 80% of the identified bacterial sequences identified. The most abundant bacterial families in the pig’s caecum and colon were Prevotellaceae (22.3%), Lactobacillaceae (17.9%), Lachnospiraceae (8.9%), Clostridiaceae (5.8%), Bacteroidaceae (5.4%), Veillonellaceae (5.4%) and Rumminococcaceae (3.7%) as reported by Tröscher-Mußotter et al, (2019). In cattle, the core microbiome of the rumen displays a distinct profile (Lamendella et al, 2011). This core microbiome in the rumen changes when diet-type changes between forage and high grain diets. Bacteroidetes and Firmicutes are the core phyla in the rumen of cattle consuming all diet types. When cattle are fed a high grain diet, Proteobacteria become the dominant phyla. With forage based diets, the Ruminococcaceae and Lachnospiraceae families are most prevalent. These changes in the core microbiota of the rumen, suggest it may be possible to effect changes in the rumen microbiota with seaweed polysaccharides.

Figure 1: The fibre profile of brown, green and red seaweeds expressed as the median reported value in g/kg of dry weight (Overland et al, 2018).

SEAWEED POLYSACCHARIDES
Unique polysaccharides or fibre found only in seaweed, account for around 30-75% of the dry weight of seaweeds, where they serve a structural role in cell walls (Xu et al, 2017). Of the total fibre in seaweed, only a proportion are soluble polysaccharides, posessing prebiotic activity. The soluble polysaccharides comprise around 55–65 % of total fibre in commonly used green and red seaweed but may be above 80 % in commonly used brown seaweed (Lahaye 1991; Figure 1). These soluble polysaccharides are particularly effective prebiotics in animals (Hentati et al, 2020).

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.

Figure 2: The polysaccharides in brown, green and red seaweeds (from Stiger and Deslandes, 2016).

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, recent advances in genomics techniques for assessing the GI microbiota, has shed new light on the prebiotic effect of seaweed polysaccharides on the GI microbiota profile and related physiological effects.

Furthermore, the additional bioactive properties of SPs of green seaweeds has been demonstrated using ulvans and their oligosaccharides, which have been shown to possess strong immune-modulating activities (Wany et al., 2014). Several studies have reported that sulphated polysaccharides extracted from different seaweeds, such as L. japonica, A. nodosum or U. pinnafitida have demonstrated an inhibitory effect on the growth of pathogenic bacteria (De Jesus Raposo et al, 2015). Extracts rich in either laminarin or fucoidan fibres at 0.3 and 0.24 g/kg of food, respectively, that were isolated from Laminaria spp., decreased the fecal E. coli populations in pigs and reduced bacterial load in raw meat products (McDonnel et al, 2010).

Figure 3: The relative abundance at Phyla level in broiler chickens consuming a wheat and soybean meal-based diet for 42 days.

APPLYING A SEAWEED BLEND POSITIVELY IMPACTS THE GI MICROBIOTA
A proprietary seaweed blend, including brown, green and red seaweeds was included in the diets of swine, poultry and equine at around 0.5% to 1% of daily feed intake to assess the effects on growth and productivity.

In a 42-day broiler chicken study, a proprietary seaweed blend was included at a rate of 0.5% to a wheat-soyabean based diet, the relative abundance profile of bacteria families in the ceca tended to shift towards the fimicutes (Figure 3). This shift led to a change in Fimicutes to Bacteroidegtes ratio from 17.7 to 22.6, indicating the presence of more of the important fibre degrading, butyrate producers such as the Ruminococcaceae and Lachnospiraceae (Vital et al, 2017). The broiler chickens consuming the seaweed containing diet tended (P≤0.09) to have improved body weight gain and feed conversion ratio.

In pigs, adding seaweed polysaccharides in the form of a seaweed blend to the diets of piglets over 35 days post-weaning, led to an improvement (P<0.01) or positive shift in the Firmicutes to Bacteroidetes ratio from a low of 5% to an average of 12% in the control and control with seaweed groups, respectively. The inclusion of seaweed also increased (P<0.5) the abundance of Ruminoccocaceae and Lachnospiraceae and decreased Prevotellaceae compared to the control group. At macro level, feed conversion ratio or feed efficiency was significantly improved (P=0.01) in the pigs consuming diets containing the seaweed blend.

In a trial with horses maintained at the same stable and allowed free access to hay over 12 weeks, a seaweed blend was added at 45 g per horse per day into their energy supplement. Faecal samples were collected from 5 horses at the beginning and end of the 12-week trial period. The relative abundance at bacterial family level revealed shifts in key fibre-degrading, butyrate producing families, the Ruminococcaceae and Lachnospiraceae. On the other hand, the relative abundance of Streptococcaceae and Akkermansiaceae, families that appear to increase in horses with laminitis were relatively reduced in horses consuming the seaweed blend.

CONCLUDING REMARKS
The GI microbiota which has been associated with nutrient availability and maintenance of the normal physiological status of the GI tract can be influence by the provision of prebiotic fibre. The prebiotic effect of unique, seaweed polysaccharides, that are not found in land-based plants, have been demonstrated in trials revealing positive impacts on the beneficial, butyrate-producing GI microbiota. Research has demonstrated that butyrate serves a key role in energy provision to the intestinal epithelium, modulating the immune response and affects several key metabolic pathways in the body. Initial data with whole seaweed blends suggests, seaweed polysaccharides are highly effective as prebiotics in animals. Ongoing research with seaweed seeks to further understand and optimize the prebiotic effect of seaweed polysaccharides in animals.

About Dr Jason Sands
Jason is Head of Nutrition at Ocean Harvest Technology Ltd. In this role Jason is responsible for leading research to develop technical documentation, strengthen the OceanFeed brand and support OHT’s sales and distribution teams by providing technical guidance for the OceanFeed range of products. Prior to Joining OHT, Jason worked various research and technical roles with public, academic and private companies. Jason holds a Bachelor and Master of science degrees in Animal Science from Tuskegee University and The University of Tennessee, respectively, and a PhD in Animal Nutrition from Purdue University.