Date

2022-8-01

Author

Çetin, Zeynep Başak

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Lactic acid is a multifunctional organic acid used as an acidifier, flavoring, or preservative in textile, food, pharmaceutical, and cosmetic industries. Bacterial fermentation is the most preferred method for lactic acid production, but the often-used refined sugar increases the cost of production. For this reason, a new environmentally friendly, sustainable, and low-cost carbon source is being researched. The seeds of horse chestnut are mostly used in the pharmaceutical industry for antioxidant production, while the shells are inert. In the present study, lactic acid production processes and efficiency were investigated from pre-treated horse chestnut shells as a promising raw material. In addition to separate hydrolysis and fermentation, simultaneous saccharification and fermentation technologies, a new method has been established by combining the advantages of these two processes. In the developed process, two bioreactors, one for enzymatic hydrolysis and the other for fermentation, were connected by hoses and the medium in the reactors was circulated through a pump. Thus, the optimum pH and temperature conditions required for the enzyme in the reactor used for enzymatic hydrolysis and for the microorganism in the reactor used for fermentation were provided. In addition to the effective operation of the enzyme and microorganism, the medium circulation between the reactors prevented the decrease in enzyme activity due to irreversible product inhibition. In the experiment, lactic acid titers and yields were measured by changing the temperature and pH parameters. After enzymatic hydrolysis, the total sugar in the hydrolysate was converted to 18.25 g L-1 lactic acid equivalent to a yield of 0.18 g g-1 dry horse chestnut shell by L. casei in separate hydrolysis and fermentation (SHF). In the simultaneous saccharification and fermentation process, using the same parameters, 6.45 g L-1 lactic acid concentration was produced, while the yield was 0.065 g g-1 dry horse chestnut shell. The highest lactic acid titer (42.1 g L-1) and yield (0.42 g g-1 dry horse chestnut shell) were obtained from the simultaneous saccharification and fermentation with a dual bioreactor process (SSF2). Based on the results obtained from this study, the simultaneous saccharification and fermentation with dual bioreactor method for microorganisms and enzymes, whose optimal conditions are not close to each other, gave promising results in obtaining valuable end products from lignocellulosic raw materials such as horse chestnut shells.

Subject Keywords

Horse chestnut shell, Enzymatic hydrolysis, Lactic acid, Simultaneous saccharification and fermentation

URI

https://hdl.handle.net/11511/98591

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Graduate School of Natural and Applied Sciences, Thesis