Protease production in solid state fermentation with liquid medium recycling in a stacked plate reactor and in a packed bed reactor by a local strain of 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 recycling strategy. In the SPR, advancing the start of recycling from day 5 to day 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 improved by the intermittent removal of part product, followed by addition of fresh feed, with near-peak production being sustained for 10 days and a total activity yield of 1771 U over 16 days of extract withdrawal. The best results 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 wash-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 showed an oscillating tendency. (C) 2001 Elsevier Science Ltd. All rights reserved.