Performance and homogeneity of Monascus sp. cultures in solid state fermentation in drum bioreactor with internal mixing: effects of mixing pattern.

Author(s)

Mariana de Paula Eduardo

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2010-07-08

Examining board members

Beatriz Vahan Kilikian; João Carlos Monteiro de Carvalho; David Alexander Mitchell; José Luís de Paiva; João Claudio Thomeo

• Advisor: Beatriz Vahan Kilikian

Abstract

This investigation aimed to verify the influence of mixing microbial growth, medium homogenization and heat removal within a solid state fermentation (SSF) bioreactor. The correlations obtained will help to establish the scale-up criteria. The model system involved the cultivation of the fungi Monascus sp. on rice. The assays were performed in a 40 l bioreactor under internal intermittent mixing with a cooling jacket and an air flux of 2 l.min-1 kgdm-1. The cultivations followed a rotational factorial plan: 12 to 60 paddle revolutions in 24 hours; with an interval of 2 to 12 hours between mixing events. Cellular growth rate was estimated by O2 consumption, CO2 production, and protein and ergosterol concentrations. The O2 consumption showed an 81% correlation with the revolutions pattern, and both the number of revolutions and interval between mixing events, influenced cell growth negatively. The maximal oxygen consumption rate (OUR) was reached after about 24 hours in cultivations submitted to shorter intervals between mixing events which indicates a positive effect of shaking on the fungal growth rate on the particle surface, as long as no medium compaction occurs. Thus it was concluded that the kind of used substrate (rice), whose reology was perceptively modified by the mixing process, acted harmfully on microbial respiration. If mixing is to be used in SSF bioreactors, the substrate used should have a low starch content and a high fiber content Ergosterol content showed an 85% positive correlation with the revolution pattern, indicating that the interval between mixing events is the most important factor. Assays performed with longer intervals between mixing events and greater numbers of turns achieved about 10 times higher ergosterol concentration than the others. The coefficient of variation of the moisture at five sites of the reactor represents the homogeneity, since they are related to the revolution patterns by 95%. (AU)