Dialysis Continuous Process for Ammonium-Lactate Fermentation of Whey: Experimental Tests

Abstract

Laboratory experiments were conducted to validate theoretical predictions describing a dialysis continuous process for the fermentation of whey lactose to ammonium lactate, in which the fermentor contents are poised at a constant pH by adding ammonia solution and dialyzed through a membrane against water. Dried sweet-cheese whey was rehydrated to contain 230 mg of lactose per ml, supplemented with 8 mg of yeast extract per ml, charged into a 5-liter fermentor without sterilization, adjusted in pH (5.3) and temperature (44°C), and inoculated with Lactobacillus bulgaricus. The fermentor and dialysate circuits were connected, and steady-state conditions were established. A series of such conditions was managed nonaseptically for 94 days to study the process and to demonstrate efficiency and productivity. As time progressed, the fermentation remained homofermentative and increased in conversion efficiency, although membrane fouling necessitated dialyzer cleaning about every 4 weeks. With a retention time of 19 h, 97% of the substrate was converted into products. Relative to nondialysis continuous or batch processes for the fermentation, the dialysis continuous process enabled the use of more concentrated substrate, was more efficient in the rate of substrate conversion, and additionally produced a second effluent of less concentrated but purer ammonium lactate.

Dialysis Continuous Process for Ammonium-Lactate Fermentation: Improved Mathematical Model and Use of Deproteinized Whey

“…Figure 1 shows the computer-simulated curves obtained by using the steady-state solution with the values in Table 3 to describe the correlation between one important operating parameter and the conversion efficiency, e.g., Tf versus Sf and Sd. The curves all fit closely with the superimposed points of the previous experimental results with whole whey (22).…”

“…Inoculum. The inoculum culture was obtained from the fermentor effluent (day 94) of a previous dialysis continuous fermentation (22) originally started with Lactobacillus bulgaricus 2217 (Chris Hanson's Laboratory, Milwaukee, Wis. ).…”

“…Dialysis continuous fermentation system. The experimental dialysis fermentation system was conducted continuously at a temperature of 44°C and a pH of 5.5 with essentially the same equipment as used previously (22). However, plunger-type reciprocating pumps (type " P", Bran and Lubbe, Inc., Evanston, Ill.) were used to meter the whey and water, and the pH was regulated with a different automatic device (model pH-40, New Brunswick Scientific Co., New Brunswick, N.…”

“…A background for this development exists in studies of the fermentation using whole whey as the substrate. The fermentation can be managed as a batch process (18), continuous process (11), or dialysis continuous process (4,22). The latter process relative to the nondialysis processes enables the use of more concentrated substrate, is more efficient-in the rate of substrate conversion, and additionally produces a dialysate effluent of less concentrated but purer ammonium lactate.…”

“…The expression was incorporated into a mathematical model of the dialysis continuous process generalized with dimensionless parameters so that it could be widely applied (4). The resulting improved set of equations was employed to simulate the fermentation on a digital computer, and the results were verified using previous experimental results with whole whey as the substrate (22). Further simulations were then made to guide experimental tests in which deproteinized whey was used as the substrate.…”