EVALUATION OF STEAM EXPLOSION AS PRETREATMENT IN AGAR EXTRACTION FROMGRACILARIA-DURA (C-AGARDH) J-AGARDH (GRACILARIACEAE, RHODOPHYTA)

Steam explosion was investigated as a pretreatment step in the isolati on of agar from the macroalga Gracilaria dura. As compared to conventi onal procedures, the yield of agar obtained using this method on alkal i (Na2CO3) conditioned algal material was higher. Extractions performe d first at 95-degrees-C and then at 121-degrees-C showed that the majo r fraction of the agar was extracted at 95-degrees-C, independently of the pretreatment. The efficiency of sulphate hydrolysis during steam explosion of G. dura previously conditioned in Na2CO3, was similar to that of a NaOH based alkali pretreatment. Except for a lower nitrogen content of the sample obtained after NaOH based alkali pretreatment an d a higher 6-0-methyl-beta-D-galactose content in the agar after steam explosion, the chemical composition of the agars showed no significan t difference. Agars extracted after steam explosion had melting temper ature, gel strength and apparent modulus of elasticity lower than thos e of corresponding 'native' and alkali (NaOH) pretreated samples, but comparable to those of a commercial sample.