Using Flow Cytometry to Evaluate the Stress Physiological Response of the Yeast Saccharomyces carlsbergensis ATCC 6269 to the Presence of 5-Hydroxymethylfurfural During Ethanol Fermentations

Lignocellulosic materials have been considered low-cost effective substrates for bioethanol production. However, lignocellulosic pretreatment releases toxic compounds such as 5-hydroxymethylfurfural (HMF) that is known to inhibit the yeast growth and ethanol production. In this work, flow cytometry was used to monitor the physiological response of the yeast Saccharomyces carlsbergensis ATCC 6269 in the presence of different initial HMF concentrations within the range of 0–15 g/L, in terms of cell membrane integrity, potential, and intracellular lipids. It was observed that the HMF presence affected more significantly the yeast growth than the ethanol production. At 15 g/L HMF, the yeast growth and fermentation ability were completely inhibited. The cell membrane integrity and potential decreased as the initial HMF concentration increased. At the end of the fermentation process with 10 g/L HMF, the yeast culture contained 45 % of cells with depolarized plasma membrane, 52 % of cells with permeabilized plasma membrane, and 53 % of cells with increasing reactive oxygen species (ROS) levels. Using the Nile Red stain, it was observed that intracellular polar lipids were more affected by the initial HMF concentration than the neutral lipids, probably due to the extensive membrane damage.