LIQUEFACTION OF DULSE (PALMARIA-PALMATA (L) KUNTZE) BY A COMMERCIAL ENZYME PREPARATION AND A PURIFIED ENDO-BETA-1,4-D-XYLANASE

Liquefaction of dry and fresh Palmaria palmata by food grade enzyme preparations and a purified endo-beta-1,4-D-xylanase was studied. The endo-beta-1,4-D-xylanase (EC 3.2.1.8) was purified to homogeneity from a commercial food grade enzyme prepared from Aspergillus niger. It has a molecular weight of 22 500, a pI of 3.5, is inactive toward com arabinoxylan, p-nitrophenyl-beta-D-xylose, carboxymethyl cellulose but shows a weak activity toward microcrystalline cellulose. It hydrolyzes oat and dulse xylan equally well in seawater and deionized water essentially into xylose and xylobiose. It is stable between pH 5.5 to 9.0 and 0 to 30-degrees-C and its activity is optimal at pH 4.5-5.5 and 40-60-degrees-C. It has a K(m) of 2.2 and 2.8 mg ml-1 and V(max) of 3600 and 3900 nkat mg-1 of protein on oat and dulse xylan, respectively. Acetate buffer, deionized water and seawater alone extracted 62.6 to 64.5% of the dry weight of dry dulse, but the use of commercial food grade enzyme preparations or the purified xylanase improved liquefaction to 81.2-87.1%. Xylose and galactose were the only sugars present in the soluble extracts. Deionized and seawater extracted 58.8-52.7 and 39.1-42.2% of the dry weight of the fresh algae collected in fall and summer, respectively. Only galactose was found in the seawater extract, while some xylose with galactose were measured in the deionized water extract of the fresh autumn algal sample. Purified and crude xylanase improved liquefaction of fresh algae to 79.8-81.4 and 71.9-77.9% of the fresh dry weight (fall and summer, respectively) in deionized and seawater, respectively, and increased the xylose content of the soluble fractions. Polysaccharides in the soluble residues were composed of 1,3/1,4-linked xylose, 1-linked galactose (floridoside) and 1,4-linked glucose (cellulose) and contained essentially 1,4-linked xylose and 1,4-linked glucose in insoluble fractions obtained after enzymatic treatment. The use of xylanase-containing food grade enzyme preparations improves liquefaction of Palmaria palmata, particularly from fresh alga. This study indicates that processing such as drying may modify markedly the solubility of P. palmata cell wall polysaccharides, which would imply the existence of some organization and/or other components in the fresh cell wall that lower xylan solubility in seawater.