Fermentative lactic acid production from coffee pulp hydrolysate using Bacillus coagulans at laboratory and pilot scales

Highlights

• Hydrolysis of coffee pulp recovered 70–80% of available sugars.

• Lactic acid production from hydrolysate was investigated at 2 L and 50 L scales.

• At 50 L scale productivity was highest at 4.0 g L⁻¹ h⁻¹.

• The yield was 0.78 g lactic acid per gram of sugar consumed.

• Downstream processing resulted in a 937 g L⁻¹ optical pure l(+)-lactic acid solution.

Abstract

In this study, the lignocellulosic residue coffee pulp was used as carbon source in fermentative l(+)-lactic acid production using Bacillus coagulans. After thermo-chemical treatment at 121 °C for 30 min in presence of 0.18 mol L⁻¹ H₂SO₄ and following an enzymatic digestion using Accellerase 1500 carbon-rich hydrolysates were obtained. Two different coffee pulp materials with comparable biomass composition were used, but sugar concentrations in hydrolysates showed variations. The primary sugars were (g L⁻¹) glucose (20–30), xylose (15–25), sucrose (5–11) and arabinose (0.7–10). Fermentations were carried out at laboratory (2 L) and pilot (50 L) scales in presence of 10 g L⁻¹ yeast extract. At pilot scale carbon utilization and lactic acid yield per gram of sugar consumed were 94.65% and 0.78 g g⁻¹, respectively. The productivity was 4.02 g L⁻¹ h⁻¹. Downstream processing resulted in a pure formulation containing 937 g L⁻¹ l(+)-lactic acid with an optical purity of 99.7%.