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Appl. Environ. Microbiol., Jul 1997, 2533-2542, Vol 63, No. 7
Copyright © 1997, American Society for Microbiology

Optimization of L-(+)-lactic acid production by ring and disc plastic composite supports through repeated-batch biofilm fermentation

KL Ho, AL Pometto 3rd and PN Hinz
Department of Food Science and Human Nutrition, Iowa State University, Ames 50011, USA.

Four customized bioreactors, three with plastic composite supports (PCS) and one with suspended cells (control), were operated as repeated- batch fermentors for 66 days at pH 5 and 37 degrees C. The working volume of each customized reactor was 600 ml, and each reactor's medium was changed every 2 to 5 days for 17 batches. The performance of PCS bioreactors in long-term biofilm repeated-batch fermentation was compared with that of suspended-cell bioreactors in this research. PCS could stimulate biofilm formation, supply nutrients to attached and free suspended cells, and reduce medium channelling for lactic acid production. Compared with conventional repeated-batch fermentation, PCS bioreactors shortened the lag time by threefold (control, 11 h; PCS, 3.5 h) and sixfold (control, 9 h; PCS, 1.5 h) at yeast extract concentrations of 0.4 and 0.8% (wt/vol), respectively. They also increased the lactic acid productivity of Lactobacillus casei subsp. rhamnosus (ATCC 11443) by 40 to 70% and shortened the total fermentation time by 28 to 61% at all yeast extract concentrations. The fastest productivity of the PCS bioreactors (4.26 g/liter/h) was at a starting glucose concentration of 10% (wt/vol), whereas that of the control (2.78 g/liter/h) was at 8% (wt/vol). PCS biofilm lactic acid fermentation can drastically improve the fermentation rate with reduced complex-nutrient addition.