| Discs plastic composite-supports (PCS) containing 50% agricultural products and 50% polypropylene (w/w) were produced by twin-screw high-temperature extrusion. PCS properties and ingredients (oat hulls, soybean hulls, yeast extract, soybean flour, dried red blood cells, bovine albumen, and/or salts) for Lactobacillus casei subsp. rhamnosus (ATCC 11443) biofilm formation and L(+)-lactic production was evaluated by two replications of a 2{dollar}sp{lcub}5-1{rcub}{dollar} design.; Soybean hulls, and salts decreased the hydrophobicity of PCS (P {dollar}<{dollar} 0.0001) and enhanced cells attachment (P {dollar}<{dollar} 0.03). Yeast extract enhanced the growth of free and attached cells in minimal medium (P {dollar}<{dollar} 0.0001). Bovine albumen blended with soybean hulls, yeast extract, soybean flour, and salts had the highest lactic acid concentration in the first (7.6 g/L) and twentieth (1.4 g/L) simulated repeated-batch fermentation. Under all conditions, suspended cells and polypropylene discs control gave negligible lactic-acid production and cell density.; PCS blended with bovine albumen, red blood cells, and soybean flour-leached nutrients gradually (20-30% initial leached nitrogen) and could still maintain 1 g/L lactic acid and cell density (absorbance at 620 nm:0.4-0.6) after the twentieth 20-mL simulated-repeated-batch fermentation. Polypropylene discs under all circumstances gave negligible lactic acid production and cell density. Lactic acid accumulation in PCS was shown to be mainly due to absorption and had no correlation with lactic acid production or biofilm formation.; PCS rings and discs with 35% soybean hulls, 5% yeast extract, 5% soybean flour, 5% dried bovine albumen, and 50% polypropylene were selected for long-term biofilm repeated-batch fermentation at controlled pH (5) and temperature (37{dollar}spcirc{dollar}C). The viable cells count on the PCS surface in 0.2, 0.4, and 0.8% yeast extract (YE) Lactic-Acid-Fermentation (LAF) medium (8% glucose) was {dollar}7.1times10sp9,{dollar} {dollar}8.5times10sp9,{dollar} and {dollar}2.4times10sp{lcub}10{rcub}{dollar} cfu/g PCS, respectively. PCS-bioreactors in 0.4 and 0.8% YE LAF medium shortened the lag time by 3-fold and 6-fold, respectively. PCS-bioreactors, at all YE concentration, increased LA productivity by 40-70%. PCS-bioreactors' total fermentation time with 0.2, 0.4, and 0.8% YE LAF medium were 1.4, 2.1, and 2.6 times faster than that of the control (suspended cells bioreactor), respectively. PCS-bioreactors had its fastest productivity (4.26 g/L/h) at 10% starting glucose, whereas the control (2.78 g/L/h) was at 8%. PCS biofilm lactic-acid fermentation can drastically improve fermentation rate under reduced complex nutrient addition. |
