Sequential acid and enzymic hydrolysis of sugar beet pulp

Fermentable sugars from beet pulp were obtained in a two-stage hydrolytic process. The first stage involved mild acid treatment to hydrolyze the hemicellulose, producing a pentose-rich syrup and a cellulose-rich fraction. The second stage was the enzymic saccharification of the cellulose fraction with fungal cellulases to produce a glucose-rich syrup. The acid hydrolysis stage was evaluated to optimize the type of acid, acid concentration, temperature and reaction time. Solubilization was markedly temperature-dependent, whereas the specificity of hemicellulose degradation depended on the type of acid utilized. The effects of different reaction times, enzyme-to-substrate ratios and particle sizes on the enzymic stage were studied. Both saccharification rate and the extent of final conversion to glucose were markedly affected by the enzyme-to-substrate ratio. Sugars recovered from the enzymic degradation of cellulose were partially fermented by Saccharomyces cerevisiae ATCC 4126.