L-Lactic Acid Production By Lactobacillus Casei Fermentation

Lactic acid and its derivatives are widely used in food, pharmaceutical, leather, and textile industries. Furthermore, since lactic acid has an excellent reactivity that stems from it having both a carboxylic acid and hydroxyl group, it can undergo a variety of chemical conversions into potentially useful chemicals such as propylene oxide, propylene glycol, acrylic acid,2,3-pentanedione, and lactate ester. Recently, there has been an increased interest in lactic acid production because it could be used as a raw material for the production of poly-lactic acid, a polymer used as specialty medical and environmental-friendly biodegradable plastics, which substitute for synthetic plastics derived from petroleum feedstocks.Most lactic acid bacteria require a wide range of growth factors including amino acids, specific minerals, vitamins, fatty acids, purines, and pyrimidines for their growth and biological activity. Most studies reported on lactic acid production by lactic acid bacteria were performed in media containing expensive nutrients such as yeast extract (YE) and peptone. A number of studies about the nutrients necessary for lactic acid bacteria fermentation had established a conclusion that among the various complex nitrogen sources, YE and peptone were the best choice for both microbial growth and lactic acid production. However, for the production of lactic acid as a source for commodity chemicals, YE and peptone were not cost effective. In the economic analyses for lactic acid production, material cost of YE was estimated to contribute over30%to the total production cost due to its high price, which implied an obvious need for a cheaper alternative.In order to reduce the manufacturing cost of L-lactic acid, we reported a new promising nitrogen source, soybean meal hydrolysate (SMH), for the complete replacement of yeast extract and peptone. In the exponential fed-batch fermentation, the maximum cell growth (3.70g l-1) was obtained after70.5h fermentation. The concentration of L-lactic acid was162.5g l-1, after96h fermentation. And the concentration of lactic acid was determined by high performance liquid chromatography system was190g l-1. The yield and productivity of L-lactic acid are89.7%and1.69g l-1h-1, respectively. This study suggested that SMH could provide useful basis for L-lactic acid production by Lactobacillus casei LA-04-1fermentation. In the hope of utilizing this cheap proteinaceous renewable material for the economical production of L-lactic acid, the feasibility of SMH as an alternative nitrogen source to YE and peptone was successfully demonstrated in batch and fed-batch cultures of Lactobacillus casei LA-04-1.Batch fermentation has been the method used industrially for L-lactic acid production. For the batch fermentation of lactic acid bacteria, the best results obtained in the published paper with glucose as the substrate are150.2g l-1for the final L-lactic acid concentration and1.34g l-1h-1for the productivity. However, the major disadvantage of batch fermentation is that L-lactic acid concentration and productivity decreased due to inhibition by high substrate concentration, a conventional property of batch fermentation. The development of continuous culture techniques eliminated this restriction by providing an essentially invariant microbial environment. This allowed constant, usually stable, or at least controllable growth rates that could be selected in a range from zero to approximately the maximum rate observed in a batch culture. Continuous systems with continuous high output can consequently be much more efficient in terms of fermenter productivity. Although promising results were obtained in continuous culture techniques, a membrane separation process is not without its problems. Foremost of these is accumulation of rejected solutes on the membrane surface during the course of fermentation that results in flux decline. This decreases the permeate flow rate and makes the process less cost efficient.Fed-batch culture is a batch culture fed continuously or sequentially with substrate without the removal of fermentation broth, which has the advantages of batch and continuous fermentation at the same time. Fed-batch is generally superior to batch and continuous processing, and is especially beneficial when changing nutrient concentrations affect the productivity and biomass of the desired product. However, as far as we know, until now there are few systematic reports on fed-batch fermentation for high concentration and efficient production of L-lactic acid by lactic acid bacteria. In this paper, the L-lactic acid production by anaerobic fermentation of lactic acid bacteria was studied. The effects of different fed-batch methods such as pulse fed-batch, constant feed rate fed-batch, constant residual glucose concentration fed-batch, exponential fed-batch on the fermentation of L-lactic acid were determined. According to the results of experiments, exponential fed-batch culture is an effective method for the fermentation of L-lactic acid. The maximum lactic acid concentration (210g l-1) and L-lactic acid concentration (180g l-1) in exponential feeding glucose solution (850g l-1) and yeast extract (1%) was obtained, respectively. L-lactic acid yield, the maximal dry cell weight and productivity were up to90.3%,4.30g l-1,2.14g l-1h-1, respectively. Compared with the traditional batch culture, the exponential feeding glucose and yeast extract culture showed56.5%improvement in L-lactic acid production,68.6%improvement in dry cell weight and59.7%improvement in productivity.