Optimization of Operational Parameters for Preparation of L-lactic Acid by Fermentation of Waste Tobacco Stems with Lactobacillus casei

Monofactorial experiments were performed to study the effects of six operational parameters,including fermentation means, fermentation duration, loading capacity, inoculum size, temperature and initial p H, on the preparation of L-lactic acid by the fermentation of waste tobacco stems with Lactobacillus casei XJL. According to the results of monofactorial experiments, four factors(inoculum size, loading capacity, initial p H and temperature) were selected and orthogonally tested at three levels.The results showed that: 1)Initial p H, inoculum size and loading capacity significantly affected the yield of L-lactic acid. 2)The optimum operational parameters were initial p H 7.0, loading capacity 120/250 m L(120 m L tobacco stem extraction loaded in a conical flask of 250 m L), inoculum size 7.5%(the volume ratio of transferred inoculant solution to total culture solution after inoculation), static culture for 48 hours at 37 ℃; under the above conditions, the maximum yield of L-lactic acid reached 157.50 g/kg.