Aliphatic acids (acetic, formic and levulinic acids
), furaldehydes (furfural and 5-hydroxymethyl furfural) and aromatic compound extractives are among the inhibitory compounds which vary according to the type of raw material and pretreatment conditions (temperature, residence time, pressure, pH and others) (Martin, & Jonsson, 2003; Bellido et al., 2011; Behera et al., 2014).
For example, furans (furfural and hydroxymethylfurfural), carboxylic acids (acetic acids, levulinic acids
, and formic acids), and phenolic compounds (syringaldehyde, 4-hydroxybenzaldehyde, catechol, vanillin, 4-hydroxybenzoic acid, dihydroconiferyl alcohol, coniferyl aldehyde, and syringic acid) are the most common inhibitors for ethanol production by S.
Others include phenolics formed from the partial breakdown of lignin (Ando et al., 1986; Jonsson et al., 1998; Larsson et al., 1999) and weak organic acids such as acetic acid as well as formic and levulinic acids
that are formed from the breakdown of HMF and furfural (Larsson et al., 1999; Martin and Jonsson, 2002; Martinez et al., 2001).