Production d-lactic acid from cassava starch by lactobacillus delbruekii in the semi industrial scale 16-l bioreactor

Abstract

Lactic acid is a vastly required organic used in many food, pharmaceutical, cosmetic and chemical industries. In addition, it has received an increasing attention for as a major component of the biodegradable poly lactic acid (PLA). Starch-rich agricultural raw materials such as potato, corn and wheat showed high potential as carbon sources in industrial microbial production processes. The present work focused on enhancing D-lactic acid production by Lactobacillus delbruekii through medium optimization using cassava starch as a C-source. Firstly the composition of production medium was optimized, and then the growth and lactic acid production kinetics were compared on both un-optimized and optimized medium compositions. Results showed that the optimized medium suitable for maximal lactic acid production was composed of [g/L]: cassava starch, 10; yeast extract, 2.5; peptone, 3; K2HPO4, 4; tri-Ammonium citrate, 1; MgSO4.7H2O, 0.57; MnSO4.4H2O, 0.12, FeSO4.7H2O, 0.003. Results also showed that medium optimization using one factor at time (OFAT) approach, increased lactic acid production by about 1.7-folds from that obtained in un-optimized medium compositions. Also, growth and production rates were improved. Further process optimization was achieved by transferring the process to 16-L stirred tank bioreactor. Both cell growth and production kinetics were significantly improved. Maximal volumetric productivity of 14.1 g/L was achieved after 48 h of cultivation with improved growth and production rates. This corresponded to an increase of about 2.5-folds from the maximal concentration obtained in optimized shake-flask cultivation. Accordingly, the obtained optimized semi-defined production medium can be used for large scale production process of D-lactic acid due to its efficiency in terms of product yield and medium cost.