[Protein enrichment of sugar beet bagasse for fermentation]

Abstract

Leached beet pulp is a plentiful waste in the sugar beet industry in Chile, reaching 100.000 metric tons per year on a dry basis. It represents an interesting substrate for protein upgrading through fermentation by cellulolytic organisms, because of the high content of cellulose and hemicellulose, with small amounts of protein and lignin (Table 1). The fermentation of leached beet pulp by the cellulolytic fungus Trichoderma reesei QM 9414 was studied under carbon limitation, with the celluloses as the only carbon and energy source. Nitrogen was supplied as ammonium sulphate and the medium was supplemented with other mineral salts as required for growth. Results on the kinetics of cellulose and hemicellulose degradation, level of reducing sugars in the medium, mycelial growth and production of cellulolytic enzymes are presented. Mycelial growth and related parameters were evaluated by an indirect method, based on nitrogen balances during fermentation. A yield of 0.26 g. of dry cell/g. of cellulosic substrate consumed and productivity of 0.095 g. of dry cell per liter per hour were obtained and compared with reported results on similar systems. After 40 to 45 hours of fermentation, approximately 80% of the cellulose and 45% of the hemicellulose were degraded (Fig. 2). Both, exoglucanase and endoglucanase, were induced; endoglucanase was growth associated, while exoglucanase appeared later in the growth phase, reaching its maximum activity in the stationary phase (Fig. 3). The product obtained was 30% protein and only 40 to 45% residual fiber, mostly hemicellulose. Mild acid hydrolysis has been successful in degrading hemicellulose but not cellulose, in the leached beet pulp.(ABSTRACT TRUNCATED AT 250 WORDS)