The production of lactic acid by using Lactobacillus casei and soybean hydrolysate during batch and fed-batch fermentation

• Main Authors: Wen-Ling Liao, 廖雯怜
• Other Authors: Yi-Chung Fu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/00265462759722041715

碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 97 === Lactic acid is a multifunctional chemical substance that has a three-dimensional structure, and exists in two types of optical isomers with different optical activations, namely L(+) and D(-)-Lactic acid, respectively. They are mainly produced through the methods of utilization of microbial fermentation and chemical synthesis. The polylactic acid polymer that lactic acid is capable of synthesizing possesses a high economic value that should be treated as a biodegradable material. Compared with plastic materials that cannot be decomposed naturally, it generates less waste disposal problems, and due to its low toxicity, polylactic acid has become the ideal material to use in food packages and other consumer products. The production of lactic acid is mainly performed by means of lactic acid fermentation, but the expensive nitrogen source - the fermentation substrate, has been the culprit of high manufacturing costs. Therefore, this has prompted many studies to use a low-cost nitrogen source to replace the common high-priced yeast extraction method in order to reduce the cost of lactic acid production. For this experiment we adopted the batch method utilizing Lactobacillus casei BCRC 10697 as a carbon source in molasses or glucose, using soybean extract or hydrolysate as the nitrogen source to perform fermentation in a fermentation tank. During the fermentation stage, the mycelia growing conditions of different fermented substrates, lactic acid production, production rate, glucose consumption and conversion rate, etc. were closely watched. On the other hand, the experiment also explored the different handling methods, using a soybean extract and hydrolysate as the nitrogen source, and glucose as the carbon source, batch and fed-batch methods were employed to obtain lactic acid yielding results. The results indicate that under batch fermentation conditions using soybean extract solution A and molasses as the fermentation substrates it is possible to provide lactic acid bacteria with an appropriate amount of nutrition to generate lactic acid, and also capable of reducing fermentation substrate cost. Among the different processing methods to obtain the nitrogen source, the soybean hydrolysate ranks as the best one, being capable of yielding 100.88g/L of high volume lactic acid within 72 hours under the conditions of 103g/L glucose concentration. Therefore, soybean hydrolysate is able to serve as a cheap nitrogen source that can be applied to processing in the future. In regard to the fed-batch fermentation method, we have shown that it is able to improve the inhibitory effect problem of substrate through appropriate feeding approach to increase lactic acid production. Perhaps in the future, we might attempt to separate lactic acid bacteria from the product at an appropriate fermentation time through lactic acid bacteria immobilization technique, and once again, to re-enter the feeding materials. This might be able to increase the final lactic acid production, and shorten the proliferation time while the lactic acid bacteria are being re-diluted during the feeding period. The product obtained through the appropriate and simplified processing method of using defatted soybean powder as raw material is able to replace the high-priced nitrogen source from yeast extract. Using the batch or fed-batch method of fermentation to adopt lactic acid fermentation of glucose to yield lactic acid, the Yield'' is able to reach 100%, or even exceed 100%! This shows that there is indeed a great development potential. We ought to carry out further testing to apply it to processing methods.