Conventional Lactic Acid Production

Some of the economic hurdles and process cost centers of this conventional carbohydrate fermentation process, schematically shown in Eigure 1, are in the complex separation steps which are needed to recover and purify the product from the cmde fermentation broths. Eurthermore, approximately a ton of gypsum, CaSO, by-product is produced and needs to be disposed of for every ton of lactic acid produced by the conventional fermentation and recovery process (30). These factors have made large-scale production by this conventional route economically and ecologically unattractive. 

Fig. 1. Conventional process for lactic acid production from dextrose, molasses, or whey.

Investigations on the stereochemistry of chiral semiochemicals may be carried out by (gas) chromatographic separation of stereoisomers using chiral stationary phases, e.g. modified cyclodextrins [32]. Alter natively, formation of diastereomers (e.g. Mosher s ester or derivatives involving lactic acid etc.) may be followed by separation on conventional achiral stationary phases. Assignment of the absolute configuration of the natural product will again need comparison with an authentic (synthetic) reference sample. 

A new method for the preparation of soy sauce has been developed. The new scaled-up method divides the moromi process into two processes autolysis and fermentation. Because of the utilization of high temperatures, the new process permits the production of a NaCl free autolyzate from koji. Division of the fermentation process into two separated processes permit better control of lactic acid fermentation and alcohol fermentation processed which used to require great skill. The new scale-up procedure for soy sauce production yields a product in half the time required by the traditional (conventional) method and still produces a soy sauce with high levels of the desirable Bavor component, glutamic acid. Utilization of this protocol by the soy sauce producing industry should have significant economic impact to bo producers and consumers. 

The physical properties and melt processing of PLA are similar to those of conventional packaging resins. It may thus be used as a commodity resin for general packaging application. In many aspects the basic properties of PLA lie between those of crystal PS and PET [ 14]. When plasticized by its own monomer lactic acid, PLA becomes increasingly flexible so that products that mimic PVC, LDPE, LLDPE, PP, and PS can be prepared [15]. Possible applications are espe-... 

Separation of lactic and propionic acids. The lactose fraction in the sweet whey permeate from cheese whey ultrafiltration can be fermented to produce lactic acid. In conjunction with the fermentation step, inorganic membranes have been tested in a continuous process to separate the lactic acid. This approach improves the productivity and reduces energy consumption compared to a conventional fermentation process. In addition, it produces a cell-free product. In a conventional process, some cells, although immobilized, are often detached and released to the product Zirconia membranes with a MWCX) of 20,000 daltons were operated at 42 C and a crossflow velocity of 2-5 m/s for this purpose [Boyaval et al., 1987]. The resulting permeate flux is 12-16 L/hr-m. To... 

Figure 7.2 Conventional production of lactic acid (Adapted from Zhang, Jin, and Kelly (2007). Biochemical Engineering Journal 35 251-263). With permission.

One of the most important processes in the production of biochemicals is the 40,000 tons/yr lactic acid production involving the Lactobacillus oxidation of lactose. The MBR productivity increased eightfold compared to a conventional batch reactor with a 19-fold increased biomass concentration. Even a 30-fold increased production of ethanol was found upon coupling the Saccharomyces cerevisiae fermentation to a membrane separation. Other successful industrial applications involve the pathogen-free production of growth hormones, the synthesis of homochiral cyanohydrins, the production of 1-aspartic acid, phenyl-acetylcarbinol, vitamin B12, and the bio transformation of acrylonitrile to acrylamide. 

Biological production of lactic acid is complicated primarily due to economical considerations arising from product inhibition and the required downstream processing of dilute aqueous product streams. The standard method of biological lactic acid production is the anaerobic fermentation by Lactobacillus in a batch reactor [7]. The conventional process requires the base to be added to the reactor to control the pH and the use of calcium carbonate to precipitate the lactate. This process produces a lactate salt that must be acidified (usually by sulfuric acid) to recover the lactic acid, with calcium sulfate as an undesirable by-product. 

The conventional method of lactic acid production from starchy materials such as barley, corn, potato or rice requires pretreatment by gelatinization and liquefaction. This is usually carried out at an elevated temperature of about 90-130°C for at least 15 min, followed by saccharification of the starch by amy-... 

Direct acidification with HCl or in situ production of lactic acid by a mesophilic lactic starter still dominate in the production of acid casein. A relatively recent development in the production of acid casein is the use of ion exchangers for acidification. In one such method, a portion of the milk is acidified to approximately pH 2 at 10°C by treatment with a strong acid ion exchanger and then mixed with unacidified milk in proportions so that the mixture has a pH of 4.6. The acidified milk is then processed by conventional techniques. A yield increase of about 3,5% is claimed, apparently due to the precipitation of some proteose-peptones. The resulting whey has a lower salt content than normal and is thus more suitable for further processing. The elimination of strong acid reduces the risk of corrosion by the chloride ion (Cl ) and hence cheaper equipment may be... 

Key to the proposal appears to be the use of new technology being developed at the Oak Ridge National Laboratory under Dr. Brian Davison. The new process is based on a three-phase, biparticle, fluidized-bed bioreactor, in which lactic acid, produced continuously in a fluidized bed of immobilized Lactobacillus delhreuckii, is simultaneously adsorbed onto a solid polyvinylpyridine resin moving countercurrent to the fermenter beer. In this way, the pH can be maintained at the optimum 5.5 and product inhibition of the fermentation is minimized. As a result, fermentation rates have been increased 4- to 10-fold higher than the conventional fermentation process and the acid product can be recovered by methanol extraction. 

The advantageous use of membranes in the removal of toxic compoimds produced during fermentation has been demonstrated in several fermentation systems. Increased (2.5 fold) volumetric productivities and product concentration yields (fourfold) were reported by Christen et al. [209] in ethanolic fermentations assisted by supported hquid membranes. Increased final product concentrations and yield were also reported by Xavier et al. [134] when comparing membrane-assisted extractive fermentation of lactic acid with conventional fermentations. 

---