Agar from the red seaweed, Laurencia flexilis (Ceramiales, Rhodophyta) from northern Philippines

P>The worldwide production of the gelling agent agar mainly rely on the red algae of the order Gracilariales and Gelidiales for raw material. We investigate here the potential of a species from another red algal order, Ceramiales as an agar source. The agar from Laurencia flexilis collected in northern Philippines was extracted using native and alkali treatment procedures and the properties of the extracts were determined using chemical, spectroscopic and physical methods. The native agar, 26% dry weight basis, forms a gel with moderate gel strength (200 g cm-2). Alkali-treatment did not enhance the gel strength, indicating insignificant amounts of galactose-6-sulfate residue, the precursor of the gel-forming 3,6-anhydrogalactose (3,6-AG) moieties. Furthermore, the Fourier transform infrared and chemical analysis showed low sulfate and high 3,6-AG levels, not affected significantly by the alkali treatment. Nuclear magnetic resonance spectroscopic analysis revealed 3-linked 6-O-methyl-D-galactose and 4-linked 3,6-anhydro-L-galactose as the major repeating unit of the native extract, with minor sulfation at 4-position of the 3-linked galactose residues. The native and alkali treated agars have comparably high gelling and melting temperatures, whereas the former exhibits higher gel syneresis. Laurencia flexilis could be a good source of agar that possesses physico-chemical and rheological qualities appropriate for food applications. Due to the inability of alkali treatment to enhance the key gel qualities of the native extract, it is recommended that commercial agar extraction from this seaweed would be done without pursuing this widely-used industrial procedure.