Chemistry, gelation, and enzymatic modification of seaweed food hydrocolloids

Background: Carrageenan, agar, and alginate are seaweed-derived carbohydrate hydrocolloids which are used as thickening and gelling agents in foods, pharma and biotechnology applications due to their unique gelation properties. These hydrocolloids are extracted commercially from a set of high-yielding, cultivated seaweeds (marine macroalgae). The seaweed type and biological and environmental factors during seaweed growth determine the chemical and rheological hydrocolloid properties. New insight into biosynthesis and microbial degradation of these seaweed-derived hydrocolloids includes discovery of unique enzymes that catalyze specific structural changes in the carbohydrate polymers which affect the hydrocolloid properties.

Scope and approach: In this review we describe the intricate chemical structures, gelation mechanisms and biosynthesis routes of seaweed hydrocolloids. We provide an overview of novel enzymes and enzyme reactions that catalyze changes in these hydrocolloids, and discuss how this new enzyme knowledge may enable further technological advancements in processing and applications of seaweed hydrocolloids.

Key Findings and Conclusions: The red seaweeds from the genera Kappaphycus and Eucheuma are key commercial sources of carrageenan, species from the genera Gracilaria and Gelidium are the main sources of agar, and brown seaweeds from the genera Laminaria and Macrocystis are currently the main sources of alginate. Recent progress has advanced our understanding of enzymatic reactions involved in the biosynthesis and microbial degradation of these hydrocolloids and especially uncovered unique epimerase, desulfatase, and alginate lyase processes. This new knowledge provides a basis for rethinking the sources and extraction protocols of these hydrocolloids because such enzymes can catalyze distinct molecular changes to improve the physical properties of the hydrocolloids.