Utilização da levedura residual de cervejaria como fonte de nitrogênio para cultivo de Bacillus sp.

Abstract

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.