Seasonal variations in the yield, gelling properties, and chemical composition of agars from Gracilaria eucheumoides and Gelidiella acerosa (Rhodophyta) from the Philippines

The yield, physical, and chemical properties of agars from two Philippine r ed seaweeds, Gracilaria eucheumoides and Gelidiella acei osa, were investig ated on a bimonthly basis. The yield of agar from Gracilaria eucheumoides w as at a maximum during the early rainy season (May, 29%) and at a minimum d uring the summer month of March (20%). In Gelidiella acerosa, a peak in aga r yield was also recorded in May (21%), with generally higher yields record ed during the rainy than in the dry season. Agar gel strengths fluctuated f rom 225 to 430 g cm(-2) and from 160 to 820 g cm(-2) for Gracilaria eucheum oides and Gelidiella acerosa, respectively, and both agars exhibited strong est gels in July. Significant seasonal variations were observed in the gell ing and melting temperatures of agar from Gracilaria eucheumoides, but not from Gelidiella acerosa. Sulphate content only varied slightly in agar samp les from Gracilaria eucheumoides, while a higher sulphate content was found in Gelidiella acerosa agar during the dry season. Moreover, the sulphate c ontent in G. acerosa agar fluctuated inversely with the 3,6-anhydrogalactos e content. A FT-IR analysis showed a fairly constant spectrum for temporal Gracilaria eucheumoides agar while peaks attributed to S-O vibrations inten sified in Gelidiella acerosa samples which were recorded to contain high su lphate residues and possess low gel strengths. Diagnosis of the FT-IR spect ra in the 1000-400 cm(-1) frequency range was also conducted in comparison with agarose and Gracilaria chilensis agar.