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Lactic acid production by bacterium Lactobacillus amylovorus DSM 20531T

Lactic acid and its derivatives have versatile applications. Novel utilisation of the simplest hydroxyl acid that exists in two optically active configurations, the L(+) and D(-) isomers, have increased the demand for it. Biodegradable polylactides (PLA ; L-, D- and D, L-lactide copolymers) have been studied for use in medical applications and as packaging material. Carbohydrate fermentation technology can produce the desired stereoisomer and it is an alternative to chemical synthesis of the racemic mixture of L(+)- and D(-)-lactic acid from petrochemicals. The biotechnological potential of green biomass residues, industrial by-products and traditionally waste materials are underexplored for their use as raw materials in the low-temperature and low- energy-consumption process for lactic acid production. Direct conversion of relatively cheap and complex substrates to lactic acid by bacteria possesing amylolytic and lactic acid producing potential could be employed in economically attractive bioprocesses. The lactic acid production by Lactobacillus amylovorus DSM 20531T in chemically defined media (MRS) with glucose (So = 20 g/L), sucrose (So = 10 g/L), soluble starch (So = 10 and 100 g/L) and corn flour (100 g/L, concentration of starch S0 75 g/L) was investigated. The batch fermentations were conducted in a lab-scale stirred tank bioreactor at temperature (30, 35, 40, 45 and 50°C) and pH (5.5) conditions encountered. The estimation of efficiency of the homolactic fermentations was based on high-pressure liquid chromatography (HPLC) analysis. L. amylovorus DSM 20531T grew well and produce lactic acid on glucose, sucrose and soluble starch (So = 10 g/L) with expected values for bioprocess efficiency (YP/S = 0.95-1 g /g ; Pr = 0.8-1.7 g/(L h). Under described conditions optimal temperature for starch consumption, bacterial growth and production of lactic acid is 45°C. After longer lag phase (12 h) in MRS-starch (S0 = 100 g L-1) than in MRS-starch (2 h, S0 = 10 g L-1), comparable values for productivity (Pr  1 g L-1 h-1) and yield coefficient of lactic acid (YP/S  0.9 g/g) were obtained. Production of lactic acid from corn starch by L. amylovorus DSM 20531T has to be improved. Preliminary results from batch experiments in MRS-starch medium (S0 = 10 g L-1) co-inoculated with Lactobacillus delbrueckii as an indicator strain suggest that L. amylovorus DSM 20531T is bacteriocin-producing organism.

lactic acid bacteria; SSF; HPLC; different carbohydrates; stirred tank bioreactor

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