P85: Ability of a Candida strain to produce citric acid from soy biodiesel-based glycerol

Soy biodiesel production results in a coproduct stream of glycerol, fatty acid and methylesters of fatty acids. During soy biodiesel production, raw glycerol is the major coproduct. This low value glycerol can be used to ferment a specialty chemical such as citric acid. The industrial applications of this specialty chemical include its uses as an acidulant and a chelator. In this study, the ability of the yeast Candida parapsilosis ATCC 7330 to convert different concentrations of soy-based raw glycerol to citric acid was compared. A raw glycerol-containing medium (pH 5.2) was developed and the yeast was grown in the medium at 30^oC for 168 hours with aeration. Once the yeast cells were pelleted by centrifugation, the supernatant was assayed for its citric acid content. A coupled enzyme assay monitored at 340 nanometers involving the enzymes citrate lyase, malate dehydrogenase and lactate dehydrogenase was utilized to determine citric acid concentrations. Citric acid production was found to be highest when C. parapsilosis ATCC 7330 was grown on medium containing 6% raw glycerol. The yeast produced lower levels of citric acid on the medium containing 1%, 8% or 10% raw glycerol. The highest citric acid yield by ATCC 7330 was observed when the medium contained 1% raw glycerol. In conclusion, C. parapsilosis ATCC 7330 was able to produce citric acid from different concentrations of raw glycerol in the medium but citric acid production was not proportional to the glycerol level present.