Production of lactic acid by continuous fermentation using an inexpensive raw material and a simplified method of lactic acid purification

DETAILED DESCRIPTION The invention provides a method for producing lactic acid by continuous fermentation.
In a preferred embodiment, particular methods of whey permeate media pretreatment are utilized.
More specifically, the invention provides a process for producing lactic acid from fermentation broth comprising the steps of (a) fermenting the broth with a lactic acid or lactic acid salt-producing microorganism in a fermentation zone, (b) continuously removing a product-containing broth from said zone, removing cells of said microorganism from said broth to form a cell-free product-containing stream and recycling said cells to said zone; (c) contacting said cell-free lactate-containing stream at an acidic pH with a water-immiscible liquid consisting essentially of trialkyl tertiary amines of at least 24 carbon atoms and a water-immiscible organic solvent, whereby lactic acid and lactic acid salt are extracted from said stream into a water-immiscible phase, said liquid characterized by a distribution coefficient in excess of 1.
0 for lactic acid and lactic acid salt in said liquid versus water; (d) separating said water-immiscible liquid from the mixture formed in step (c); and (e) contacting said water-immiscible phase from step (d) with a material selected from the group consisting of aqueous ammonium hydroxide, solid alkalis, solid alkaline earth compounds, and aqueous non-homogenous suspensions of solid alkalis or solid alkaline earth compounds, whereby lactic acid and lactic acid salt are removed from said water-immiscible phase.
If the fermentation broth is whey permeate, the invention further provides a method of pretreatment of the whey comprising the steps of (1) providing the whey composition at an acidic pH from which a substantial portion of proteins having a molecular weight over 10,000 have been removed by ultrafiltration, (2) treating the composition from step (1) with a protease at a temperature in the range of 40.
degree.
C.
to 65.
degree.
C.
for a period sufficient to degrade proteins to smaller peptides and amino acids, such smaller peptides and amino acids characterized as being nonprecipitable under conditions of heat sterilization, increased salt concentration, or contact with organic solvents