Abstract
Agar, alginate, and carrageenans are high-value seaweed hydrocolloids, which are used as gelation and thickening agents in different food, pharmaceutical, and biotechnological applications. The annual global production of these hydrocolloids has recently reached 100,000 tons with a gross market value just above US$ 1.1 billion. The techno-functional properties of the seaweed polysaccharides depend strictly on their unique structural make-up, notably degree and position of sulfation and presence of anhydro-bridges. Classical extraction techniques include hot alkali treatments, but recent research has shown promising results with enzymes. Current methods mainly involve use of commercially available enzyme mixtures developed for terrestrial plant material processing. Application of seaweed polysaccharide targeted enzymes allows for selective extraction at mild conditions as well as tailor-made modifications of the hydrocolloids to obtain specific functionalities. This review provides an update of the detailed structural features of κ-, ι-, λ-carrageenans, agars, and alginate, and a thorough discussion of enzyme assisted extraction and processing techniques for these hydrocolloids.
Highlights
Hydrocolloids can be defined as substances that interact with water to form colloid systems either in the form of a gel or a sol system of solubilized particles
The currently used hydrocolloid polysaccharides are derived from plant, microbial, and seaweed sources: pectin is, for example, extracted from apple pomace and citrus peel; xanthan gum is prepared by aerobic fermentation from Xanthomonas campestris, and agar, alginates, and carrageenans are obtained from brown and red seaweeds
Commercial carrageenans are extracted from the carrageenophyte red seaweed genera Kappaphycus, Gigartina, Eucheuma, Chondrus, and Hypnea, in which the carrageenans comprise up to 50% of the dry weight [4]. κ-Carrageenan is mostly extracted from Kappaphycus alvarezii, known in the trade as Eucheuma cottonii, while ι-carrageeman is predominantly produced from Eucheuma denticulatum, known as Eucheuma spinosum. λ-Carrageenan is obtained from seaweeds within the Gigartina and Chondrus genera, which as sporophytic plants produce λ-carrageenan while they make a κ/ι-hybrid as gametophytic plants [4,5]
Summary
Hydrocolloids can be defined as substances that interact with water to form colloid systems either in the form of a gel or a sol system of solubilized particles. The currently used hydrocolloid polysaccharides are derived from plant, microbial, and seaweed sources: pectin is, for example, extracted from apple pomace and citrus peel; xanthan gum is prepared by aerobic fermentation from Xanthomonas campestris, and agar, alginates, and carrageenans are obtained from brown and red seaweeds. The Asia-Pacific region dominates seaweed cultivation production, followed by countries such as, Chile, Tanzania, and Madagascar [2]. In these countries, seaweed farming has had positive socio-economic benefits on the coastal communities by improving the economic and social livelihood for the people living in the coastal areas and has reduced overfishing [3]. This review describes the chemistry, properties, and applications of the three seaweed-derived hydrocolloids, carrageenans, agar, and alginate, with a focus on novel enzyme-assisted processing techniques. The use of enzymes, allows for reduction of chemicals in seaweed hydrocolloid extraction and holds enormous potential for creation of sustainable processing of seaweed polysaccharides
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