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Capillary Electrophoresis as a Tool for Evaluating Lactic Acid Production from Sorghum

¹USDA-ARS GMPRC, 1515 College Ave., Manhattan, KS 66502. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 785-776-2708. Fax: 785-537-5534. E-mail: tilman.schober@ars.usda.gov ³Dept. Biological and Agricultural Engineering, Kansas State University, Manhattan, KS 66506.

Sorghum is an underutilized resource for the production of bioindustrial chemicals like lactic acid. Capillary electrophoresis (CE) was tested to monitor the fermentation process, i.e., quantify the amount of lactic acid and by-products in the fermentation broth using phosphate buffer pH 6.25 containing the electroosmotic flow modifier cetyltrimethylammonium bromide (CTAB). High levels of calcium carbonate were required during fermentation to stabilize the pH and these caused considerably prolonged migration times in CE. A 1:10 dilution of the samples with water was the best way to reduce salt load and thus conductivity in the sample plug, and thus to eliminate the problem of prolonged migration times. Further improvements were achieved by rinsing the capillary with HCl and water after each run, rather than NaOH and water. HCl might more efficiently remove Ca²⁺ ions from the capillary surface. The fermentation broth studied was based on liquefied sorghum inoculated with Rhizopus oryzae. The main product was lactic acid (24.60 ± 0.56 g/L) and a significant by-product was fumaric acid (1.07 ± 0.04 g/L).