CONTINUOUS PROPIONATE PRODUCTION FROM WHEY PERMEATE USING A NOVEL FIBROUS BED BIOREACTOR

Continuous production of propionate from whey lactose by Propionibacte rium acidipropionici immobilized in a novel fibrous bed bioreactor was studied. In conventional batch propionic acid fermentation, whey perm eate without nutrient supplementation was unable to support cell growt h and failed to give satisfactory fermentation results for over 7 days . However, with the fibrous bed bioreactor, a high fermentation rate a nd high conversion were obtained with plain whey permeate and de-lacto se whey permeate. About 2% (wt/vol) propionic acid was obtained from a 4.2% lactose feed at a retention time of 35 to 45 h. The propionic ac id yield was similar to 46% (wt/vol) from lactose. The optimal pH for fermentation was 6.5, and lower fermentation rates and yields were obt ained at lower pH values. The optimal temperature was 30 degrees C, bu t the temperature effect was not dramatic in the range of 25 to 35 deg rees C. Addition of yeast extract and trypticase to whey permeate hast ened reactor startup and increased the fermentation rate and product y ields, but the addition was not required for long-term reactor perform ance. The improved fermentation results with the immobilized cell bior eactor can be attributed to the high cell density, similar to 50 g/L, attained in the bioreactor. Cells were immobilized by loose attachment to fiber surfaces and entrapment in the void spaces within the fibrou s matrix, thus allowing constant renewal of cells. Consequently, this bioreactor was able to operate continuously for 6 months without encou ntering any clogging, degeneration, or contamination problems. Compare d to conventional batch fermenters, the new bioreactor offers many adv antages for industrial fermentation, including a more than 10-fold inc rease in productivity, acceptance of low-nutrient feedstocks such as w hey permeate, and resistance to contamination. (C) 1994 John Wiley & S ons, Inc.