Production of l-lactic acid by Rhizopus oryzae using semicontinuous fermentation in bioreactor

Abstract

Semicontinuous fermentation using pellets of Rhizopus oryzae has been recognized as a promising technology for L-lactic acid production. In this work, semicontinuous fermentation of R. oryzae AS 3.819 for L-lactic acid production has been developed with high L-lactic acid yield and volumetric productivity. The effects of factors such as inoculations, CaCO₃ addition time, and temperature on L-lactic acid yield and R. oryzae morphology were researched in detail. The results showed that optimal fermentation conditions for the first cycle were: inoculation with 4% spore suspension, CaCO₃ added to the culture medium at the beginning of culture, and culture temperature of 32-34 °C. In orthogonal experiments, high L-lactic acid yield was achieved when the feeding medium was (g/l): glucose, 100; (NH₄)₂SO₄, 2; KH₂PO₄, 0.1; ZnSO₄·7H₂O, 0.33; MgSO₄·7H₂O, 0.15; CaCO₃, 50. Twenty cycles of semicontinuous fermentation were carried out in flask culture. L: -lactic acid yield was 78.75% for the first cycle and 80-90% for the repeated cycles; the activities of lactate dehydrogenases (LDH) were 7.2-9.2 U/mg; fermentation was completed in 24 h for each repeated cycle. In a 7-l magnetically stirred fermentor, semicontinuous fermentation lasted for 25 cycles using pellets of R. oryzae AS 3.819 under the optimal conditions determined from flask cultures. The final L-lactic acid concentration (LLAC) reached 103.7 g/l, and the volumetric productivity was 2.16 g/(l·h) for the first cycle; in the following 19 repeated cycles, the final LLAC reached 81-95 g/l, and the volumetric productivities were 3.40-3.85 g/(l·h).

L‐lactic acid production by Rhizopus oryzae MBG‐10 using starch‐rich waste loquat kernels as substrate

“…At the other CaCO 3 concentrations (0, 10, and 30 g/L), determined pHs were 4.4, 5.1, and 6.0, respectively. Optimal CaCO 3 concentration of 20 g/L was lower than those reported in the previous studies [25][26][27]. For example, Wu et al [27] reported that the maximum lactic acid production by R. oryzae was achieved when 50 g/L CaCO 3 were used as neutralizing agent.…”

Zygomycetes-based biorefinery: Present status and future prospects

“…Glucose, however, has been reported to yield up to 0.90 g/g L-lactic acid (Wu et al, 2011), which also surpasses the yield and productivity, using xylose as substrate. Some improvements have nevertheless been made towards xylose conversion into L-lactic acid.…”

“…In the cell growth stage, the zygomycetes are kept in a relatively rich medium. In the production stage, the produced biomass is cultivated in a nitrogen-limited medium to promote production of organic acids (Wu et al, 2011). Additional requirements for the organic acid production are oxygen-rich conditions and a neutralizing agent to maintain the pH-value in the medium (Zhang et al, 2007).…”

Lactic Acid Production to Purification: A Review

“…Rhizopus species, such as R. oryzae and R. arrhizus, have amylolytic enzymatic activity, which enables them to convert starch directly to L(+)-lactic acid. Several studies have reported on the use of Rhizopus for lactic acid production (Yin et al 1998;Liu et al 2006;Yu et al 2007;Guo et al 2010;Wu et al 2011;Saito et al 2012). Fig.…”