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.