The fermentation of sugarcane molasses by Dekkera bruxellensis and the mobilization of reserve carbohydrates

Abstract

The yeast Dekkera bruxellensis is considered to be very well adapted to industrial environments, in Brazil, USA, Canada and European Countries, when different substrates are used in alcoholic fermentations. Our previous study described its fermentative profile with a sugarcane juice substrate. In this study, we have extended its physiological evaluation to fermentation situations by using sugarcane molasses as a substrate to replicate industrial working conditions. The results have confirmed the previous reports of the low capacity of D. bruxellensis cells to assimilate sucrose, which seems to be the main factor that can cause a bottleneck in its use as fermentative yeast. Furthermore, the cells of D. bruxellensis showed a tendency to deviate most of sugar available for biomass and organic acids (lactic and acetic) compared with Saccharomyces cerevisiae, when calculated on the basis of their respective yields. As well as this, the acetate production from molasses medium by both yeasts was in marked contrast with the previous data on sugarcane juice. Glycerol and ethanol production by D. bruxellensis cells achieved levels of 33 and 53 % of the S. cerevisiae, respectively. However, the ethanol yield was similar for both yeasts. It is worth noting that this yeast did not accumulate trehalose when the intracellular glycogen content was 30 % lower than in S. cerevisiae. The lack of trehalose did not affect yeast viability under fermentation conditions. Thus, the adaptive success of D. bruxellensis under industrial fermentation conditions seems to be unrelated to the production of these reserve carbohydrates.

High intracellular trehalase activity prevents the storage of trehalose in the yeastDekkera bruxellensis

“…In exponentially growing cells of Dekkera bruxellensis the intracellular content of trehalose was quantified as low as 0·15 μ g Eq.glucose/10 7 cell, reaching near 2 μ g Eq.glucose/10 7 cell in stationary phase, which is in accordance with the lack of trehalose storage we have previously reported (Pereira et al . ). This lack of storage might be related either to limitation of synthesis or to a fast turnover of the metabolite in this yeast.…”

“…On the other hand, we did not observe trehalose accumulation when D. bruxellensis cells following exposure to high sugar concentration during molasses fermentation (Pereira et al . ). The lack of further activation indicated that in D. bruxellensis N‐trehalase does not respond to PKA pathway.…”

“…; Pereira et al . ). Cells were maintained and cultivated in YPD medium with glucose (111 mmol l −1 ) as carbon source as described by Leite et al .…”

“…This yeast shares some characteristics with Saccharomyces cerevisiae which allows for an anaerobic growth and leads to high fermentation levels, contrasting to its tendency to oxidative metabolism due to high respiration capacity (Leite et al 2013). On the other hand, we have previously reported that D. bruxellensis does not accumulate trehalose as S. cerevisiae does, and so no mobilization of this metabolite is observed during fermentation of sugarcane molasses (Pereira et al 2014). It seems that both accumulation and mobilization of trehalose are important traits for yeast cells to survive to the fermentation processes (Pataro et al 2002;Basso et al 2011).…”

“…On the other hand, we have previously reported that D. bruxellensis does not accumulate trehalose as S. cerevisiae does, and so no mobilization of this metabolite is observed during fermentation of sugarcane molasses (Pereira et al . ). It seems that both accumulation and mobilization of trehalose are important traits for yeast cells to survive to the fermentation processes (Pataro et al .…”