ALGINATE DEGRADATION DURING ANAEROBIC-DIGESTION OF LAMINARIA-HYPERBOREA STIPES

Polyphenols and divalent metal ions present in the tissue may seriousl y affect the degradation of alginate during anaerobic digestion of bro wn seaweeds. Laminaria hyperborea stipes, harvested at 59 degrees N of f the Norwegian coast in the autumn, were degraded at different concen trations of polyphenols in anaerobic batch reactors at 35 degrees C an d pH 7. This was done by removing or adding the mechanically peeled ou ter phenolic layer of the algae, and using methanogenic and alginate d egrading inocula already adapted to L. hyperborea degradation. Initial alginate released from the algal particles was affected by NaOH titra tions because the Ca/Na-ratio was reduced. After a rapid consumption o f the mannitol, alginate lyases were induced, and guluronate lyases sh owed the highest extracellular activity. Then the microbes digested 0. 12-0.23 g Na-alginate L-1 h(-1). Later the degradation rate of alginat es declined almost to zero, and 13-50% of the alginate remained insolu ble. The total solubilisation of alginates was apparently limited by b oth Ca-crosslinked guluronate residues and complexation with compounds such as polyphenols. The methane production had a lag phase that incr eased at higher amounts of soluble polyphenols, and the total fermenta tion probably also became product inhibited if soluble compounds such as acetate, ethanol and butyrate were accumulated.