Inhibitory
Activity of Carbonyl Compounds on Alcoholic
Fermentation by Saccharomyces cerevisiae
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Abstract
Aldehydes and acids play important
roles in the fermentation inhibition
of biomass hydrolysates. A series of carbonyl compounds (vanillin,
syringaldehyde, 4-hydroxybenzaldehyde, pyrogallol aldehyde, and <i>o</i>-phthalaldehyde) were used to examine the quantitative
structure–inhibitory activity relationship of carbonyl compounds
on alcoholic fermentation, based on the glucose consumption rate and
the final ethanol yield. It was observed that pyrogallol aldehyde
and <i>o</i>-phthalaldehyde (5.0 mM) reduced the initial
glucose consumption rate by 60 and 89%, respectively, and also decreased
the final ethanol yield by 60 and 99%, respectively. Correlating the
molecular descriptors to inhibition efficiency in yeast fermentation
revealed a strong relationship between the energy of the lowest unoccupied
molecular orbital (<i>E</i><sub>LUMO</sub>) of aldehydes
and their inhibitory efficiency in fermentation. On the other hand,
vanillin, syringaldehyde, and 4-hydroxybenzaldehyde (5.0 mM) increased
the final ethanol yields by 11, 4, and 1%, respectively. Addition
of vanillin appeared to favor ethanol formation over glycerol formation
and decreased the glycerol yield in yeast fermentation. Furthermore,
alcohol dehydrogenase (ADH) activity dropped significantly from 3.85
to 2.72, 1.83, 0.46, and 0.11 U/mg at 6 h of fermentation at vanillin
concentrations of 0, 2.5, 5.0, 10.0, and 25.0 mM correspondingly.
In addition, fermentation inhibition by acetic acid and benzoic acid
was pH-dependent. Addition of acetate, benzoate, and potassium chloride
increased the glucose consumption rate, likely because the salts enhanced
membrane permeability, thus increasing glucose consumption