Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441

Process variables and concentration of carbon in media were optimised for l actic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the expe rimental area (80-160 g l(-1)). The highest lactic acid concentration in ba tch fermentation, 118.6 g l(-1), was obtained with 160 g l(-1) glucose. The maximum volumetric productivity, 4.4 g l(-1) h(-1) at 15 h, was achieved a t an initial glucose concentration of 100 g l(-1). Similar lactic acid conc entrations were reached with a fedbatch approach using growing cells. in wh ich case the fermentation time was much shorter. Statistical experimental d esign and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 3 5 degreesC, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (2 2 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the, growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lacti c acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).