Tuesday, April 20, 2010
11-56

Citric acid production by Candida guilliermondii on soy biodiesel-based glycerol

Thomas P. West, Biology and Microbiology, South Dakota State University, Box 2104, Brookings, SD 57007

The ability of the yeast Candida guilliermondii to utilize raw glycerol from the processing of soy biodiesel for citric acid production was examined. A raw glycerol coproduct is formed during the transesterification of soybean oil for biodiesel production. There are a number of commercial applications of the specialty chemical citric acid relative to its uses in foods, beverages and pharmaceuticals. The yeast species C. guilliermondii ATCC 9058 was utilized in this work. A raw glycerol-containing medium (pH 5.2) was developed and the yeast was grown in the medium at 30oC for 168 hours with aeration. The yeast cells were pelleted by centrifugation and the resultant supernatant was assayed for its citric acid content. To determine citric acid content, a coupled enzyme assay involving the enzymes citrate lyase, malate dehydrogenase and lactate dehydrogenase was used where the reaction was monitored at 340 nanometers. Citric acid production was found to be highest when C. guilliermondii was grown on medium containing 6% raw glycerol. The yeast produced lower levels of citric acid on the medium containing 1% or 3% raw glycerol. The citric acid yield by ATCC 9058 was highest on the medium containing 1% raw glycerol. In conclusion, C. guilliermondii ATCC 9058 produced citric acid from raw glycerol with the level of citric acid production being dependent upon the raw glycerol concentration present in the medium.

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