Protease production in solid state fermentation with liquid medium recycling in a stacked plate reactor and in a packed bed reactor by a local strainof Rhizopus oryzae

Protease production by the solid state fermentation (SSF) of wheat bran by a local strain of Rhizopus oryzae, was studied in a stacked plate reactor ( SPR) and a packed bed reactor (PBR), incorporating the liquid medium recycl ing strategy. In the SPR, advancing the start of recycling from day 5 to da y 3 almost doubled production from 364 units (U) to 600 U (total activity). Doubling the number of plates from five to ten (each plate having 2 g bran ) resulted in only a 25% increase in production to 750 U. Production was im proved by the intermittent removal of part product, followed by addition of fresh feed, with near-peak production being sustained for 10 days and a to tal activity yield of 1771 U over 16 days of extract withdrawal. The best r esults were obtained in the PER, in which the total activity yield of 6381 U, was four times that from the SPR. Rapid changes, including a 'product wa sh-out' effect, as observed by adapting the dilution rate concept, occurred in the PER but not in the SPR. Total enzyme and total protein yields showe d an oscillating tendency. (C) 2001 Elsevier Science Ltd. All rights reserv ed.