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Continuous Process for Ammonium-Lactate Fermentation of Deproteinized Whey

Department of Microbiology and Public Health, Michigan State University, East Lansing 48824

ABSTRACT

A mathematical model was developed to describe a process for the continuous fermentation of lactose to lactic acid with neutralization to a constant pH by ammonia. Equations for the steady state were used to simulate the effect of cell-retention time on substrate, product, and cell-mass concentrations in a single-stage system. The theoretical predictions then were validated by laboratory experiments in which reconstituted and supplemented deproteinized whey was fermented continuously by an adapted culture of Lactobacillus bulgaricus at pH 5.5 and 44 C without sterilization or asepsis. Lactate concentration was maximum (58.7 mg/ml) at a cell-retention time of 27 h, and cell mass was maximum (1.9 mg/ml) at 9.3 h. The single-stage continuous fermentation of deproteinized whey as compared to that of whole whey resulted in similarly high product accumulation and of substrate utilization at similarly high conversion rates. The fermentation of deproteinized whey also was simulated for operation with two stages in series at various retention-time ratios, the results of which predicted that the combined retention time could be reduced to 17 h with results as good as that with the single-stage operation.