Abstract
L-Lactic acid is a promising three-carbon building-block chemical, widely used in the food, pharmaceutical, leather and textile industries and Rhizopus oryzae is an important filamentous fungus for the production of L-lactic acid with high optical purity. This study investigated the medium compositions for the maximum biomass cultivation of R. oryzae L-lactic acid fermentation, and optimized the operation parameters for semi-continuous repeated fermentation in a stirred tank fermentor using response surface method (RSM) analysis. The results indicated that a higher biomass cultivation of 3.750±0.05 g/L was achieved when the medium was composed of 12% (w/v) glucose, 0.4% (w/v) ammonium sulfate and 0.045% (w/v) monopotassium phosphate. The optimal fermentation conditions for the initial batch were as follows: the aeration was 0.75 L/(L·min), inoculation of germs was 11% and agitation speed was 560 rpm. The fermentative intensity of the initial batch and the sequentially repeated batches with self-immobilized pelletized R. oryzae were 2.162 g/(L·h) and 3.704 g/(L·h), respectively. Key words: Self-immobilized, Rhizopus oryzae, pellet, lactic acid, response surface method (RSM).
Highlights
L-Lactic acid is a natural chemical, widely used as acidulant, flavor and preservative in the food, pharmaceutical and leather industries (Efremenko et al, 2006; Rojan et al, 2007; Gullon et al, 2008)
This study investigated the medium compositions for the maximum biomass cultivation of R. oryzae L-lactic acid fermentation, and optimized the operation parameters for semi-continuous repeated fermentation in a stirred tank fermentor using response surface method (RSM) analysis
The results indicated that a higher biomass cultivation of 3.750±0.05 g/L was achieved when the medium was composed of 12% (w/v) glucose, 0.4% (w/v) ammonium sulfate and 0.045% (w/v) monopotassium phosphate
Summary
L-Lactic acid is a natural chemical, widely used as acidulant, flavor and preservative in the food, pharmaceutical and leather industries (Efremenko et al, 2006; Rojan et al, 2007; Gullon et al, 2008). It can further be polymerized into polylactic acid, which is applied in biodegrable plastics and textile fiber production. This environmental friendly polymer attracts the interest of the researchers all over the world (Zhang et al, 2007; Sauer et al, 2008; Maneeboon et al, 2010). The relationship between morphology of R. oryzae and lactate productivity was investigated for the purpose of enhancing the conversion rate of glucose
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