SOUZA, Rafael Limongi de.; FREIRE, Kristerson Reinaldo de Luna.; ALMEIDA, Andréa Farias de.
Résumé:
Brazil produces about 2.5 million tons / year of wet waste (malt bagasse
and residual yeast) from breweries. The residual brewer's yeast has about 70-80%
moisture, 45-50% total proteins and 10-20% soluble nitrogen, being a possible source of
nitrogen compounds. The objective of this work was to process the residue of brewer's
yeast aiming its use as a nutritional source for the cultivation of Bacillus sp. The wet
brewery residue was recovered, debarked, autolysed, fractionated and its crude extract
purified. The residue was characterized for pH, nitrogen composition and total protein.
After preparation of the residue, it was added in culture medium. In this work, the culture
of Bacillus sp was carried out with three compositions of culture medium differing in the
nitrogen source: Medium A (commercial yeast extract), Medium B (brewer's residual
yeast extract + ammonium) and Medium C (extract of residual brewer's yeast). Samples
were evaluated for pH, microbial growth and substrate concentration, as well as the
following kinetic parameters: μmax, Px and Yx/s. The extract of residual brewer's yeast
presented in its characterization 4.5% of total nitrogen and 39% of total protein and pH
of 6.41. During the process there was a decrease in pH for the cultures with Medium A
and B. The culture with Medium C did not change pH, remaining between 6.6 and 6.8.
Analyzing the parameters, cultures with Mediums B and C presented higher yields (Px)
and conversion factors (Y x/s) similar to the medium A (control) culture. These results
show that the use of the residual brewer's yeast extract has potential as a source of
organic nitrogen for the submerged culture of Bacillus sp.
