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

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.

Dietary Supplementation with Fumaric Acid Improves Growth Performance in Nile Tilapia Juveniles

Organic acids have recently been identified as promising replacements for antibiotics in aquafeeds that promote fish growth and feed efficiency. This study evaluated the inclusion of fumaric acid (FA; 0, 5, 10, 15, 20, and 30 g/kg) in diets (350 g/kg CP; 3.4 kcal digestible energy/g) of Nile tilapia juveniles. Fish (average weight 1.7 ± 0.1 g) were distributed in three 40 L aquaria per treatment (13 fish/aquaria) in a completely randomized design. Over 35 days, the fish received the experimental diets three times daily to apparent satiety. The maximum weight gain, feed efficiency ratio, and protein efficiency ratio were recorded in fish supplemented with 14–15 g/kg FA. After 28 days, Enterobacteriaceae was registered only in the gut of tilapia without FA augmentation. Gram-negative bacteria in the fish gut decreased (p < 0.05) in fish receiving 17 g/kg of dietary FA, increased after this level. The intestinal villi height and width were affected (p < 0.05) by FA levels and feeding time. Thus, inclusion of 15 g/kg of FA was effective in promoting growth, improving intestinal morphometry, and decreasing negative gut bacteria of Nile tilapia juveniles after 35 days.

Four- and Five-Carbon Dicarboxylic Acids Present in Secondary Organic Aerosol Produced from Anthropogenic and Biogenic Volatile Organic Compounds

To better understand precursors of dicarboxylic acids in ambient secondary organic aerosol (SOA), we studied C4–C9 dicarboxylic acids present in SOA formed from the oxidation of toluene, naphthalene, α-pinene, and isoprene. C4–C9 dicarboxylic acids present in SOA were analyzed by offline derivatization gas chromatography–mass spectrometry. We revealed that C4 dicarboxylic acids including succinic acid, maleic acid, fumaric acid, malic acid, DL-tartaric acid, and meso-tartaric acid are produced by the photooxidation of toluene. Since meso-tartaric acid barely occurs in nature, it is a potential aerosol tracer of photochemical reaction products. In SOA particles from toluene, we also detected a compound and its isomer with similar mass spectra to methyltartaric acid standard; the compound and the isomer are tentatively identified as 2,3-dihydroxypentanedioic acid isomers. The ratio of detected C4–C5 dicarboxylic acids to total toluene SOA mass had no significant dependence on the initial VOC/NOx condition. Trace levels of maleic acid and fumaric acid were detected during the photooxidation of naphthalene. Malic acid was produced from the oxidation of α-pinene and isoprene. A trace amount of succinic acid was detected in the SOA produced from the oxidation of isoprene.