Optimization Of L-Lactic Acid Fermentation Process Based On The Parameters Correlation

Lactic acid is an important organic acid. With wide application and market prospect, lactic acid and its derivatives has become the focus in recent years. In several main methods of lactic acid production,the technology of microbial fermentation has an absolute advantage because of its low cost, wide source of raw materials and so on..In this paper, Bacillus coagulans being experimental strain, the study focused on the problem of higher residual sugar and heteropoly acid content in the end of lactic acid fermentation, and developed by fermentation and extraction process optimization. Central composite design method combined with mass spectrometry analysis were used to control conditions of fermentation process for lower residual sugar and mixed acid. With single factor and orthogonal experiment methods, active carbon absorption was used to remove the residual sugar from crude lactic acid in the extraction process. The results are as follows:(1)The change law of fermentation parameters and their relations were studied by parameter correlation analysis in the control process. pH and OUR were main factors that affect the residual sugar utilization and heteropoly acid generated.(2) In50L fermentor, fermentation process was optimized to reduce residual sugar and heteropoly acid content by controlling pH and OUR. The optimized conditions were0-16h pH5.0-5.2, I6h-Glu1.5%pH6.3-6.5, and then pH5.8-5.9,, OUR0.7-0.8mol/m3·h. Under the conditions,,residual sugar decreased from0.35-0.4%to0.2%, the mixed acid content decreased from0.33mol/L to0.067mol/L or so.(3) The optimal conditions of50L were used in20T and60T fermentor for scale-up experiment. Compared with50L, the results of scale-up were different. The content of residual sugar and mixed acid reached about0.3%and0.133mol/L. The results might be due to the absence of agitator, and additional alkali was difficult to well-mix in a short time, that would result in partial acid or alkali. Higher pH could aggravate the uneven phenomenon.(4) In order to find out the reasons of scale-up experiment, simulation experiment of flow field in50L fermentor was conducted. The stirring speed was0and150rpm,experimental results show that gas flow rate and shear distribution weren’t uniform without agitation, and the dead space was obvious. With the fermentor volume increase, the phenomenon was more seriously.(5) According to the results of simulation experiment, lower pH was used to alleviate the problem of uneven mixing. The controlled conditions were0-16h pH5.0-5.2,16h-Glu=1.5%pH6.0-6.2, and then5.6-5.8, OUR0.7-0.8mol/m3·h. The experimental results show that mixed acid content in20T fermentor was the same as that in50L fermentor basically. But, residual sugar in60T fermentor was slightly higher, up to0.28%.(6) In extraction process, with single factor and orthogonal experiment methods, active carbon absorption was used to remove the residual sugar. The experimental results showed that powdered carbon quantity was the most significant factor to removal of sugar. The optimal conditions were70℃,60min, and carbon quantity6%. Under the conditions, the maximum removal rate could attain57%..