Kinetic characteristics of long-term repeated fed-batch (LtRFb) l-lactic acid fermentation by a Bacillus coagulans strain

Abstract

Application of degradable plastics is the most critical solution to plastic pollution. As the precursor of biodegradable plastic PLA (polylactic acid), efficient production of l-lactic acid is vital for the commercial replacement of traditional plastics. Bacillus coagulans H-2, a robust strain, was investigated for effective production of l-lactic acid using long-term repeated fed-batch (LtRFb) fermentation. Kinetic characteristics of l-lactic acid fermentation were analyzed by two models, showing that cell-growth coupled production gradually replaces cell-maintenance coupled production during fermentation. With the LtRFb strategy, l-lactic acid was produced at a high final concentration of 192.7 g/L, on average, and a yield of up to 93.0% during 20 batches of repeated fermentation within 487.5 h. Thus, strain H-2 can be used in the industrial production of l-lactic acid with optimization based on kinetic modeling.

Keywords: Bacillus coagulans; Kinetics; Long‐term repeated fed‐batch; l‐Lactic acid.

FIGURE 1

Time curves of residual glucose (A), OD₆₀₀ (B), and l‐lactic acid (C), and the histogram of yields (D) during fermentation for optimization of pH. Symbols for different fermentation conditions in (A), (B), and (C): ●, pH 6.2; ■, pH 6.5; ▲, pH 7.0; ▼, pH 7.5

FIGURE 2

Time curves of residual glucose (A), OD₆₀₀ (B), and l‐lactic acid (C), and the histogram of yields (D) during fermentation for optimization of temperature. Symbols for different fermentation conditions in (A), (B), and (C): ●, 50°C; ■, 52°C; ▲, 55°C; ▼, 57°C

FIGURE 3

Time curves of residual glucose (A), OD₆₀₀ (B), and l‐lactic acid (C), and the histogram of yields (D) during fermentation for optimization of initial glucose concentration. Symbols for different fermentation conditions in (A), (B), and (C): ●, 140 g/L initial glucose; ■, 160 g/L initial glucose; ▲, 180 g/L initial glucose; ▼, 200 g/L initial glucose; ◆, 220 g/L initial glucose

FIGURE 4

Time curves of residual glucose (A), OD₆₀₀ (B), and l‐lactic acid (C), and the histogram of yields (D) during fermentation for optimization of inoculation volume. Symbols for different fermentation conditions in (A), (B), and (C): ●, 10% (v/v) inoculation volume; ■, 20% (v/v) inoculation volume; ▲, 30% (v/v) inoculation volume

FIGURE 5

Time curves of OD₆₀₀ (A) and l‐lactic acid (B), and the histogram of yields (C) during LtRFb fermentation. In (A), the OD₆₀₀ curves for the odd and even fermentation batches are indicated by dashed and solid lines, respectively

FIGURE 6

Fitting curves of OD₆₀₀ (A) and l‐lactic acid concentration (B) in batch 20, and kinetic parameters (C) of 20 batches in LtRFb fermentation based on kinetic models. Symbols for different parameters in (C): ○, product of α and μ_m in product simulation; ■, β in product simulation