Alginate lyase activity and acidogenesis during fermentation of Laminaria hyperborea

The initial hydrolysis and acidogenesis of L. hyperborea fronds were invest igated in anaerobic batch fermentations. The main product in the acidogenes is of fronds and fronds added extra substrates was acetate. Addition of ext ra glucose led to a diauxic development with glucose as the preferred subst rate and delayed initiation of alginate lyase activity. Addition of extra m annitol did not affect the initiation of lyase activity, but maximum activi ty was reduced. Addition of products such as acetate and propionate also re sulted in a delayed lyase activity. The fermentation of pure fronds resulte d in a high acetate/CO2 ratio, suggesting that the homoacetogenic pathway p layed an important role in the degradation of uronic acids. Addition of man nitol or glucose resulted in a much lower acetate/CO2 ratio and an initial decrease in soluble COD concentration, probably caused by biomass growth an d possibly some H-2 production. Thus, the seasonal changes of mannitol and laminaran in L. hyperborea fronds will result in different digestion charac teristics for this algae throughout the year.