Carrageenans: Biological properties, chemical modifications and structural analysis – A review

Abstract

Carrageenans are sulphated linear polysaccharides of d-galactose and 3,6-anhydro-d-galactose extracted from certain red seaweeds of the Rhodophyceae class. They have been extensively used in the food industry as thickening, gelling and protein-suspending agents, and more recently by the pharmaceutical industry as excipient in pills and tablets. Besides the well-known biological activities related to inflammatory and immune responses, carrageenans are potent inhibitors of herpes and HPV viruses and there are indications that these polysaccharides may offer some protection against HIV infection. Thus, this review describes important aspects of carrageenans related to their industrial/therapeutic applications, physicochemical properties and structural analysis. Moreover, chemical modifications of carrageenans that can lead to prototypes with potential application for the treatment of several diseases, such as herpes, HPV and AIDS, will be outlined.

Introduction

Over the last years, marine microorganisms such as bacteria, microalgae and seaweeds have represented a large source of valuable materials (DeLong, 1997, Rasmussen and Morrissey, 2007). The various unique carbohydrate residues that are found in marine organisms are especially interesting and emphasize the importance of obtaining further knowledge in this area (Michel, Nyval-Collen, Barbeyron, Czjzek, & Helbert, 2006). So far, the three commercially exploited carbohydrate polymers from marine organisms are: (1) alginates, the mannuronic-acid- and guluronic-acid-containing polymers from brown seaweeds; (2) agar, the d-galactose and 3,6-anhydro-l-galactose-containing polymers that are isolated from red seaweeds; and (3) carrageenans (De Ruiter and Rudolph, 1997, Selby and Whistler, 1993).

Carrageenan is a generic name for a family of polysaccharides, obtained by extraction from certain species of red seaweeds (Rhodophyta) (Van De Velde, Knutsen, Usov, Rollema, & Cerezo, 2002). The word carrageenan is derived from the colloquial Irish name for this seaweed, carrageen, which means “little rock”. The aqueous extraction of red seaweeds to obtain these hydrophilic colloids is known in Ireland since 1810 (Stanley, 1987). All seaweeds that produce carrageenan as their main cell-wall material belong to Rhodophyta, but there is almost no information available on the biosynthesis of carrageenans and the genetics of the seaweed plant cell wall (De Ruiter & Rudolph, 1997).

In the food industry, carrageenans are widely utilized due to their excellent physical functional properties, such as thickening, gelling and stabilizing abilities, and have been used to improve the texture of cottage cheese, to control the viscosity and texture of puddings and dairy desserts, and as binders and stabilizers in the meat-processing industry for the manufacture of patties, sausages and low-fat hamburgers.

The food industry accounts for 70–80% of the total world production, estimated at about 45,000 metric tonnes per year, of which about 45% goes to dairy products and 30% to meat and meat derivatives. The total market of carrageenans has been estimated as US $300 million/year (McHugh, 2003).

Carrageenans are also used in various non-food products, such as pharmaceutical, cosmetics, printing and textile formulations (Imeson, 2000). Carrageenans stabilize toothpaste preparations, absorb body fluids when formulated in wound dressings and interact with human carotene to give soft skin and silky hair in hand lotions and shampoos, respectively. They have proved to be useful as tableting excipients due to the good compatibility, high robustness and persistent viscoelasticity of the tablet during compression. These interesting properties indicated that carrageenans are suitable excipients for sustained-release formulations (Bhardwaj, Kanwar, Lal, & Gupta, 2000).

Therefore, considering the extensive applications of carrageenans, the aim of this review article is to present a comprehensive overview of recent and relevant aspects related, principally, to their biological activities, chemical modifications and structural analysis.