Production and Purification of <span style="font-variant: small-caps">l</span>-lactic Acid in Lab and Pilot Scales Using Sweet Sorghum Juice

• Main Authors: Agata Olszewska-Widdrat, Maria Alexandri, José Pablo López-Gómez, Roland Schneider, Michael Mandl, Joachim Venus
• Format: Article
• Language: English
• Published: MDPI AG 2019-04-01
• Series: Fermentation
• Subjects: fermentation; lactic acid; downstream; sweet sorghum juice; <i>Bacillus coagulans</i>
• Online Access: https://www.mdpi.com/2311-5637/5/2/36

Sweet sorghum juice (SSJ) was evaluated as fermentation substrate for the production of <span style="font-variant: small-caps;">l</span>-lactic acid. A thermophilic <i>Bacillus coagulans</i> isolate was selected for batch fermentations without the use of additional nutrients. The first batch of SSJ (Batch A) resulted on higher lactic acid concentration, yield and productivity with values of 78.75 g∙L^&#8722;1, 0.78 g∙g^&#8722;1 and 1.77 g∙L^&#8722;1 h^&#8722;1, respectively. Similar results were obtained when the process was transferred into the pilot scale (50 L), with corresponding values of 73 g∙L^&#8722;1, 0.70 g∙g^&#8722;1 and 1.47 g∙L^&#8722;1 h^&#8722;1. A complete downstream process scheme was developed in order to separate lactic acid from the fermentation components. Coarse and ultra-filtration were employed as preliminary separation steps. Mono- and bipolar electrodialysis, followed by chromatography and vacuum evaporation were subsequently carried out leading to a solution containing 905.8 g∙L^&#8722;1 lactic acid, with an optical purity of 98.9%. The results of this study highlight the importance of the downstream process with respect to using SSJ for lactic acid production. The proposed downstream process constitutes a more environmentally benign approach to conventional precipitation methods.