Enhanced Sorbitol Production under Submerged Fermentation using Lactobacillus plantarum

Background and Objective: Sorbitol is a non-toxic and slightly hygroscopic compound with different applications. Zymomonas mobiles produces sorbitol from sucrose or mixtures of glucose and fructose (formation is coupled with the dehydrogenation of glucose to glucono-δ- lactone). Recombinant Zymomonas mobilis may produce sorbitol and gluconic acid from glucose and fructose using different divalent metal ions with reduced the ethanol yield and significantly increased yield of sorbitol. Current study envisaged to alter the media components, physical process parameters and supplementation of amino acids for enhanced sorbitol production. Material and Methods: Several process variables were evaluated on sorbitol production including carbon sources (glucose, fructose, maltose, sucrose), carbon concentrations (5, 10, 20 and 25 g l^-1), nitrogen sources (peptone, tryptone, yeast extract, beef extract and organic nitrogen mix), temperatures (25, 29, 33, 37, 41°C), pH (6, 6.5, 7 , 7.5 ,8), agitation rate (50, 100, 150, 200 rpm) and amino acids (cysteine, cystine, tryptophan)in batch cultivation of Lactobacillus plantarum NCIM 2912. Shake flask cultivation performed under optimum conditions like temperature 37°C, pH 7.0 and agitation rate of 150 rpm, resulted in enhanced sorbitol production. Comparative study of sorbitol production in solid state fermentation and submerged fermentation was also evaluated. Results and Conclusion: Batch cultivation under submerged conditions further performed in 7.5^-l lab scale bioreactor (working volume 3.0^-l) under optimized conditions resulted in maximum cell biomass of 8.95±0.03 g g^-1 and a sorbitol content of 9.78±0.04 g l-1 after 42.0 h of fermentation. Scale up study on bioreactor resulted in maximum sorbitol yield (Yp/x) and productivity of 1.11 g g^-1 and 0.50 g l^-1 h under submerged fermentation, respectively.