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    • Article

      Monthly variation of agar quality of some gracilarioids from the Philippines (Rhodophyta, Gracilariaceae) 

      MRJ Luhan, MSR Ferrer, J Tanaka & Y Aruga - The Philippine Scientist, 2004 - San Carlos Publications, University of San Carlos
      Species of the economically important gracilarioid seaweeds from the Philippines were studied to determine the monthly variation in agar quality. Yield, gel strength, melting and gelling temperatures, and sulfate contents were compared. Lowest agar yield was observed in Gracilaria changii in July (4.15%) and highest in Gracilariopsis heteroclada in March (20.84%). Gel strength was lowest in G. heteroclada in November (44 g cm-2) and highest in Gracilaria tenuistipitata in January (874 g cm-2). Melting temperature was lowest in G. heteroclada in November (68.7°C) and highest also in G. heteroclada in January (90.3°C). Gelling temperature was lowest at 34.4°C in G. changii and Gracilaria firma in November and December, respectively; and highest in G. heteroclada in October (45°C). Sulfate content was lowest in G. firma in November (0.16%) and highest in G. heteroclada in February (2.71%).

      The variation in the agar parameters could be due to different composition of agars of different species. Sulfate is significantly lower in Gracilaria firma. Yield is significantly higher in Gracilariopsis heteroclada. There is no significant difference in the gel strength, melting and gelling temperatures among species.
    • Book chapter

      Yield and agar quality of three red seaweed Gracilaria species grown in tanks at three salinities 

      MSR Ferrer & AN Marasigan - In T Bagarinao (Ed.), Research Output of the Fisheries Sector Program, 2007 - Bureau of Agricultural Research, Department of Agriculture
      Gracilaria changii, G. firma and G. tenuistipitata were collected from the eastern coast of Sorsogon in southeastern Philippines and grown in concrete tanks at the SEAFDEC Aquaculture Department in Iloilo in May-June and in September-October 1994 at a stocking density of 1 kg/m2 and at three salinities (15, 25, and 35 ppt). In the first run, the highest specific growth rates per day were 2.5% at 25 ppt for G. changii, 3.6% at 35 ppt for G. firma, and 3.2% at 15 ppt for G. tenuistipitata. In the second run, the highest daily growth rates were 1.4% for G. changii, 1.2% for G. firma, and 3.3% for G. tenuistipitata, all at 15 ppt. Nutrient and light limitation in the second run led to lower and even negative growth rates. Gracilaria changii and G. firma were euryhaline but grew best at 25–35 ppt; G.tenuistipitata was not euryhaline and grew best at 15 ppt. The highest growth rates in tanks were at salinities close to those in the natural habitat: G. changii at 25 ppt, G. firma at 35 ppt, and G. tenuistipitata at 15 ppt. The estimated potential production (dry weight kg/m2-yr) in tanks was 1.65 kg G. changii at 25 ppt, 2.49 kg G. firma at 35 ppt, and 2.35 kg G. tenuistipitata at 15 ppt.

      Agar yields from three Gracilaria species varied from 5% to 23%, on average lowest in G. tenuistipitatata, and were generally higher at 25 ppt and 35 ppt than at 15 ppt. Agar gel strengths were also strongly affected by salinity and were highest at 35 ppt. Gracilaria tenuistipitata had very high gel strength (average 782 g/cm2 but as high as 1,082 g/cm2 comparable to agarose), well above the specified 750 g/cm2 for the international market. Gracilaria changii and G. firma had average gel strengths of 516 and 558 g/cm2, well within the range (400–600 g/cm2) for commercial agar used in the food industry. The sulfate contents were lower at 15 ppt and were even 0% in several instances, especially in G. tenuistipitata. The gelling temperature of 32°C and melting temperature of 97.3°C qualifies G. tenuistipitata for the international market. Gracilaria changii and G. firma had melting temperatures of 93–95°C but gelling temperatures of just 29°C. Farming techniques for these seaweeds should be developed to produce enough raw material for profitable commercial processing.