Population dynamics of yeasts inhabiting bioethanol production with cell recycling

Abstract

Seeking to understand the dynamics of the yeast population in a bioethanol fermentation process that uses cell recycling, the yeast inhabiting the fermentation tanks throughout the production season were monitored. A total of 26 yeasts were isolated from tanks in a Brazilian bioethanol distillery plant during six different periods of the season. These yeasts were evaluated with regard to fermentative capacity and all yeasts were qualified to be used for bioethanol production. Based on the numerical taxonomy, it was possible to say that they were all representative of Saccharomyces sensu stricto. A total of 10 different banding patterns were obtained from the 16 strains isolated. This work has shown that the yeast introduced at the beginning of the season was quickly replaced by one or more native yeast strains. It was also shown that the replacement of these strains is not always harmful to the process and isolating such yeasts found in the fermentation tanks could be an interesting strategy for new strain selection.

Artisanal cachaça and brewer's spent grain as sources of yeasts with promising biotechnological properties

“…The highlighted part shows the limits expected for commercial strains. The shaded region in chart represents the limits described for strains with good fermentative capacity by Tosin and Andrietta ().…”

“…This type of medium guarantees the absence of external factors, including contamination by chemical agents and nutritional variations due to processing, which can affect the parameters under study (Borges et al . ; Tosin and Andrietta ). Also, the carbon source concentration (150 g l −1 sucrose) of the synthetic medium is compatible with the concentration used in industrial ethanolic fermentation processes.…”

“…The preparation of the culture medium and the analyses and the fermentation experiments were performed as described by Tosin and Andrietta (). The fermentations were carried out in Erlenmeyer (250 ml) with 100 ml of sterile medium (150 g l −1 sucrose (Synth), 6·0 g l −1 yeast extract (Difco, Detroit, MI), 5·0 g l −1 potassium phosphate dibasic (Synth), 1·0 g l −1 magnesium sulphate heptahydrate (Synth), 1·0 g l −1 potassium chloride (Synth)).…”

“…After the run, the agarose gel was stained for 40 min with ethidium bromide and washed with TAFE buffer (0·5 μ l ml −1 ) for 30 min. The resulting gel was analysed under ultraviolet light (UVP BioImagem System, Upland, Canada) (Tosin and Andrietta ).…”

“…These statistical analyses were performed using software Assistat ver. 7.7 pt—free software—2017 (Campina Grande, Brazil; Silva and de Azevedo ). SensoMaker ver.…”