Abstract
Fumaric acid is widely used in the food and beverage, pharmaceutical and polyester resin industries. Rhizopus oryzae is the most successful microorganism at excreting fumaric acid compared to all known natural and genetically modified organisms. It has previously been discovered that careful control of the glucose feed rate can eliminate the by-product formation of ethanol. Two key parameters affecting fumaric acid excretion were identified, namely the medium pH and the urea feed rate. A continuous fermentation with immobilised R. oryzae was utilised to determine the effect of these parameters. It was found that the selectivity for fumaric acid production increased at high glucose consumption rates for a pH of 4, different from the trend for pH 5 and 6, achieving a yield of 0.93 gg−1. This yield is higher than previously reported in the literature. Varying the urea feed rate to 0.255 mgL−1h−1 improved the yield of fumaric acid but experienced a lower glucose uptake rate compared to higher urea feed rates. An optimum region has been found for fumaric acid production at pH 4, a urea feed rate of 0.625 mgL−1h−1 and a glucose feed rate of 0.329 gL−1h−1.
Highlights
The global market is experiencing a shift towards more renewable feedstocks and procedures
All of the fermentations were conducted with immobilised R. oryzae in a bio-reactor, which allowed for the control of the fermentation conditions
An experimental run consisting of around 200 h remained at constant pH and urea addition rate while the glucose feed rate was altered
Summary
The global market is experiencing a shift towards more renewable feedstocks and procedures. This is largely motivated by the drive to find alternatives to crude oil-derived chemicals. Focus has been brought onto the production of bio-based chemicals from renewable carbohydrate sources [1,2]. Dicarboxylic acids are one group that have been identified to be ideal bio-based platform chemicals. Malic acid and succinic acid were highlighted as they are produced in the tricarboxylic acid (TCA) cycle. They are not readily excreted by many organisms in large quantities
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