Production of lactic acid using facultative anaerobic bacteria : optimization

• Main Author: Nurulsuriani, Awang
• Format: Undergraduates Project Papers
• Language: English
• Published: 2015
• Subjects: TP Chemical technology
• Online Access: http://umpir.ump.edu.my/id/eprint/12749/1/FKKSA%20-%20NURULSURIANI%20AWANG%20-%20CD%209533.pdf; http://umpir.ump.edu.my/id/eprint/12749/

Lactic acid (CH3-CHOHCOOH) is the most widely occurring carboxylic acid, having a prime position due to its versatile applications in industries. The use of cheap raw material is important as the price for lactic acid in the market is not too high. This research was done to optimize the production of lactic acid using mixed culture of facultative anaerobic bacteria and banana stem waste (BSW) as the substrate. The inoculum used for this research was probiotic milk drink (PMD). The fermentation process was done by varying the temperature and the fermentation time in 250 mL Erlenmayer flask. The temperature and fermentation time were the factors chosen in this research. The temperature range used was 37-41°C, while the range for fermentation time was 18-22 ours. Fermentation process was done without agitation and the ratio of BSW: PMD was 4:1; 40 ml of BSW was mixed with 10 ml of inoculum. The total experiment runs were 13 runs. Design Expert 7.0 software was used to set the total number of experimental runs and the range for the factors chosen. The samples from the fermentation process were then analyzed using High Performance Liquid Chromatography (HPLC) and the optimum condition was determined using Response Surface Methodology (RSM). The range for the lactic acid concentration from the experimental result was 0.010 mg/mL to 0.0155 mg/mL. Validation experiment was done to validate suggested optimum condition. Design Expert 7.0 software suggested a total of two validation runs. The fermentation time was maintained at 20 hours. The only parameter that was changed in this validation experiment was the temperature which at 38°C and 39°C. The error from the validation experiment was 0.06 %. In conclusion, Central Composite Design (CCD) and RSM enabled the determination of optimal operating conditions for obtaining greater lactic acid production. The optimization of the analyzed responses demonstrated that the best results for lactic acid production (0.16 g/g) were obtained at 39 °C and fermentation time at 20 hours. The yield of lactic acid at the optimum condition was 0.16 g/g while its concentration was 0.014 mg/mL.