Continuous Production of Fumaric Acid with Immobilised Rhizopus oryzae: The Role of pH and Urea Addition

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.

The Effect of pH, Metal Ions, and Insoluble Solids on the Production of Fumarate and Malate by Rhizopus delemar in the Presence of CaCO3

“…It is also critical to highlight that a variation in the amount of H + would result in differences in the amounts of alkali required to control the pH. This is because the acids present may either be as fully dissociated, aqueous undissociated, or solid undissociated acid forms [13]. The stoichiometry of organic acid production and accompanying H + production as a function of pH at standard ambient temperature was previously presented by Taymaz et al [33].…”

“…The study found an optimum region for FA production at pH 4, a urea feed rate of 0.625 mg L −1 h −1 , and a glucose feed rate of 0.329 g L −1 h −1 . Moreover, pH 6 was found to be the least favourable condition with regard to FA production [13]. This section of the research study was therefore considered additive, comparing the previously unstudied pH 7 condition to the other three (4, 5, and 6) [13], with a special focus on investigating the conditions that result in MA production.…”

“…R. delemar will be used henceforth in this research for clarity purposes. Compared against the metric above, R. delemar is the most successful fumaric acid producer, with the highest yield reported as 0.93 g g −1 in homofumarate production using immobilised fungus [13]. Additionally, significantly high productivities have been reported from immobilised R. delemar with a rotary biofilm contactor and an adsorption column [14].…”

“…Based on the work on A. oryzae [3,26], three factors were likely responsible for the observed response. These were insoluble solids, metal ions, and pH [13,24,27].…”

“…Increasing CaCO 3 concentrations beyond the amounts required for neutralisation means that the pH would be maintained throughout the duration of the fermentation [18]. In a recent study, Swart et al [13] found that higher pH conditions (pH 6) were unfavourable for fumaric acid production with R. delemar. The findings clearly indicated that the three-fold increase in osmotic and ionic stresses, compared to the pH 4 condition, resulted in the production of unwanted byproducts, including malic acid.…”