Presence of Low Concentrations of Acetic Acid Improves Fermentations using Saccharomyces cerevisiae

Darren Greetham

doi:10.4172/2155-9821.1000192

Abstract

Fermentation of sugars released from lignocellulosic biomass (LCMs) is potentially a sustainable option for the production of bioethanol. LCMs release fermentable hexose sugars and the currently non-fermentable pentose sugars; ethanol yield from lignocellulosic residues is dependent on the efficient conversion of available sugars to ethanol. One of the challenges facing the commercial application for the conversion of lignocellulosic material to ethanol is the presence of inhibitors released by the breakdown of plant cell walls. Presence of acetic acid is an inevitable side-effect for the release of fermentable sugars from the deconstruction of plant cell walls, increasing temperatures used for the pre-treatment process releases acetic acid from the lignin component of the plant cell wall. Using phenotypic microarray analysis revealed that low concentrations (20 mM) acetic acid augmented metabolic output in yeast for an initial period, however, assays at higher concentrations (>50 mM) reduced metabolic output. Fermentations in the presence of acetic acid where characterized by an improved fermentation efficiency in assays containing 20 mM acetic acid compared with control conditions, however, efficiency was reduced in assays using 50 mM acetic acid. Yeast cells in the presence of 20 mM acetic acid produced less glycerol, and produced more ATP when compared with control conditions or in the presence of 50 mM acetic acid.

Highlights

Short-chain weak organic acids are potent inhibitors of microbial growth and are widely applied as preservatives in food and beverages
Presence of acetic acid (0-100 mM) on metabolic output was assessed with a reduction in metabolic output observed at 75 mM acetic acid and no metabolic output observed in an assay containing 100 mM acetic acid (Figure 1A)
Low concentrations of acetic acid (

Summary

Introduction

Short-chain weak organic acids are potent inhibitors of microbial growth and are widely applied as preservatives in food and beverages. The toxicity of acetic acid and other weak organic acids is pH dependent, as it is the un-dissociated form which passively enters the yeast cell [4]. Un-dissociated acetic acid that diffuses through the cell membrane will become dissociated intracellularly [5], the degree of dissociation will depend on the cytosolic pH. In order to maintain a constant intracellular pH, protons are transported across the cell membrane through the activity of ATPases [5]. This results in an increase in ATP consumption and addition of acetate to a media has been shown to lower biomass produced [6]

Methods

Results

Conclusion