Alginate lyase activity and acidogenesis during fermentation of Laminaria hyperborea

The initial hydrolysis and acidogenesis of L. hyperborea fronds wereinvestigated in anaerobic batch fermentations. The main product in theacidogenesis of fronds and fronds added extra substrates was acetate.Addition of extra glucose led to a diauxic development with glucose as thepreferred substrate and delayed initiation of alginate lyase activity. Additionof extra mannitol did not affect the initiation of lyase activity, butmaximum activity was reduced. Addition of products such as acetate andpropionate also resulted in a delayed lyase activity. The fermentation ofpure fronds resulted in a high acetate/CO₂ ratio, suggesting that thehomoacetogenic pathway played an important role in the degradation ofuronic acids. Addition of mannitol or glucose resulted in a much loweracetate/CO₂ ratio and an initial decrease in soluble CODconcentration, probably caused by biomass growth and possibly someH₂ production. Thus, the seasonal changes of mannitol and laminaranin L. hyperborea fronds will result in different digestion characteristicsfor this algae throughout the year.