Furans are probably the most important group of inhibitors, since the fermentability of hydrolysates obtained by acidification is inversely related to the concentration of these compounds. In addition, phenolic compounds cause loss of integrity in biological membranes, affecting their ability to serve as selective barriers and enzyme matrices [59]. Acetic acid, the main aliphatic compound present, is released from acetyl-hemicellulose groups. In turn, formic acid is a product of HMF degradation.