초록
<P><B>Abstract</B></P> <P>Short chain fatty acid fermentation was carried out using <I>Lactobacillus buchneri</I> ATCC 4005 under anoxic conditions at low pH values using xylose as substrate. Fermentation studies were conducted with free cells and with cells immobilized on alumina fibers in batch, fed-batch, and continuous reactors. The results indicate that xylose is readily utilized by <I>L. buchneri</I> as a carbon source with an estimated maximum specific growth rate (µ<SUB>max</SUB>) of 0.15 h<SUP>−1</SUP> for free cell and immobilized cell fermentations. Lactic and acetic acids were produced at high concentration levels of 67 g L<SUP>−1</SUP> and 32 g L<SUP>−1</SUP>, respectively in fed-batch fermentation without any apparent cell inhibition. Volumetric productivities of 6.4 g L<SUP>−1</SUP>h<SUP>−1</SUP> for lactic acid, and 4.3 g L<SUP>−1</SUP>h<SUP>−1</SUP> for acetic acid were obtained at a dilution rate of 0.5 h<SUP>−1</SUP>. The Luedeking-Piret model that relates cell growth to product formation is utilized to develop a mathematical model of the continuous fermentation system. The model predictions for volumetric acid productivities as a function of dilution rates are presented, and are shown to agree well with experimental data. This study is the first demonstration of a continuous fermentation process for the conversion of xylose to lactic and acetic acids using <I>L. buchneri</I> at a pH value of 4.0.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First report on continuous low pH bacterial fermentation on short chain fatty acid production. </LI> <LI> Batch fermentation kinetics of <I>L</I>. <I>buchneri</I> using xylose was established. </LI> <LI> High lactic (67 g L<SUP>−1</SUP>) and acetic acid (32 g L<SUP>−1</SUP>) levels were achieved in fed-batch fermentation. </LI> <LI> High acid productivities were achieved in immobilized cell fermentation systems. </LI> <LI> A mathematical model could describe changes in productivity with different dilution rates. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>