Agars from three species of Gracilaria (Rhodophyta) from Yucatan Peninsula Y. Freile-Pelegrın a, * , E. Murano b,c a Department of Marine Resources, CINVESTAV-Unidad Merida, A.P. 73 Cordemex, Merida, 97310 Yucatan, Mexico b POLY-bios Research Center and POLY-tech, AREA di Ricerca di Trieste, Padriciano 99, 34012 Trieste, Italy c PROTOS Research Institute, P.O. Box 972, 34100 Trieste, Italy Received 16 August 2002; received in revised form 2 February 2004; accepted 18 April 2004 Available online 21 July 2004 Abstract Gracilaria cervicornis, Gracilaria blodgettii and Gracilaria crassissima growing along the coasts of Yucatan were investigated for their agar content. The effect of different concentrations of NaOH in the alkali treatment was evaluated. The three species of Gracilaria produced agars, both native and alkali treated, with different properties confirming the heterogeneity of the agar polymers in this genera. G. cervicornis produces agar polymers with an occurrence of methoxylation and sulphation at the C-6 of the b-D- galactose residues, and with an extra methylation due to the presence of the 4-O-methyl-a-L -galactose residue. The presences of these residues is responsible for the extremely poor gelling ability of its agarocolloids, whose commercial value seems to be quite low. Agar extracts from G. blodgettii showed the typical pattern of unsubstituted agar with a very low degree of methylation on both galactose residues. The discrepancy found between sulphate content and NMR data of agar from this species requires a more detailed structural investigation. G. crassissima produces a good quality agar after sulphate precursor sequences have been removed by alkaline treatment, and it may be considered for exploitation as a source of commercial grade agar. Alkali treatment was effective both in removing alkali-labile sulphate and increasing the gel strength in G. crassissima but not in G. cervicornis and G. blodgettii. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Agar; Gracilaria; Seaweed 1. Introduction Gracilaria is one of the genera that comprises the greatest number of species in the family Gracilariaceae (Rhodophyta), with the majority of them being reported from warm-water and tropical regions. Currently, this genus is the major world-wide agar source. Adoption of the alkali treatment, which improves agar quality, and the development of suitable cultivation techniques, have allowed to the genus Gracilaria to complement the lack of quantities of Gelidium for agar industry (Armisen, 1995). Gracilaria spp. produce a complex mixture of galactans of the agar-type containing several extremes in structure with different substituents, whose type (sul- phate esters, methoxyls and pyruvic acid), amount and location strongly affect the physical properties of the gel. The molecular structure of agar polysaccharides, par- ticularly the type and location of sulphate esters, ap- pears to be species-specific (Craigie, 1990). The amount of sulphate which is alkali-labile can be lowered using an appropriate alkali treatment before agar extraction, leading to an increase in gel strength. The nature of the chemical structure of agars from Gracilaria spp. allows new uses in food industry. The low gel strength of the native agars of this genus, together with a low syneresis index (due to the high sulphate content), permits their use as gelling agents for spread foods, soft-texture con- fectionery and as a fat replacer. A comprehensive knowledge of agar chemistry is a pre-requisite for understanding its rheological properties and final use. Nuclear magnetic resonance and infrared spectroscopy have been shown to be effective methods for structural characterisation of these polysaccharides (Murano, 1995). Numerous structural studies on the agars of different species of Gracilaria have contributed to their selection for use in industry, i.e. Gracilaria chilensis Bird, McLachlan and Oliveira (Matsuhiro and * Corresponding author. Fax: +52-999-9812917. E-mail address: freile@mda.cinvestav.mx (Y. Freile-Pelegrın). 0960-8524/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2004.04.010 Bioresource Technology 96 (2005) 295–302