Agar quality of commercial agarophytes from different geographical origins: 1. Physical and rheological properties

Abstract

Six economically important species ofGracilaria, from a number of commercial sources around the world, andGracilariopsis lemaneiformis, collected from two Japanese localities, were used as the sources of raw material for the evaluation of agar quality. Agar-agar was extracted by pretreatment with various concentratrions of NaOH (0%, 3%, 5%, 7%, 10%) incubated at 80 °C for 2 h. Agar yield, viscosity, dynamic gelling and melting temperature and gel texture were determined for 1.5% agar gels. The highest agar yield was obtained fromG. gracilis from Argentina (39.5%), while the lowest was from BrazilianG. gracilis (13.37%). Dynamic gelling temperature was highest in the agar fromG. gracilis from Turkey (59 °C) and lowest in the non-alkali treated agar isolated fromG. edulis from Indonesia (46 °C). Melting temperature ranged from 96 °C in the agars from the JapaneseGracilariopsis andG. chilensis from Chile to 69 °C in the non-alkali treated agar fromG. edulis from Indonesia. In general, all species produced an agar with high gel strength after treatment with 5% NaOH, except forG. chilensis and the twoGracilariopsis species, which produced an agar with high gel strength after treatment with 3, 7 and 10% NaOH. The highest gel strength (2056 ± 13.6 cm⁻²) and hardest gel (261 ± 19.89 g mm⁻²) were obtained fromG. lemaneiformis from Japan (Oita Prefecture) after treatment with 7 and 10% NaOH respectively. The lowest gel strength (351 ± 93 cm⁻²) was obtained fromG. gracilis from Brazil after treatment with 3% NaOH. The softest gel (66.31 ± 9.63 g mm⁻²) was isolated fromG. tenuistipitata from China, after treatment with 3% NaOH. The most flexible gel (11.62 ± 0.31 g mm⁻² × 10²) was obtained fromG. chilensis from Chile after treatment with 3% NaOH.