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Modified alginate as immobilization matrix and barrier between two-phase liquid system: implementation in D-/L-lactic acid production and beyond

Direct conversion of starch to lactic acid is routinely and efficiently performed under industrially applicable conditions by Lactobacillus amylovorus DSM 20531T. This simultaneous semi-solid substrate saccharification and fermentation (s5f) type of bioprocess can be further upgraded and become a part of a highly integrated process for production of lactate esters from starch. In our work, modified alginate was used as immobilization system of L. amylovorus DSM 20531T cells. Spherical beads with dimeter of 4.0 ± 02 mm containing the strain cells and starch were formed under mild conditions and used as biocatalyst in s5f batch experiments that were carried out over several days at 45C, 150 rpm and noncontrolled pH. Immobilized biocatalyst maintained high metabolic activity within matrix and hydrolized starch from starch-loaded-beads to maltooligosaccharides (maltohexaose, maltotetraose, maltotriose and maltose) and glucose, and fermented simple carbohydrates thereof to D-/L-lactic acid, as quantified by HPLC methods. Use of starch caused disintegration of soft and flexible beads that otherwise were stable and retained their size, shape and color under harsh conditions, including absolute ethanol, sulfuric acid solution and combination of the two unfavourable substances. Micromolar amounts of ethyl lactate that was formed in such two- phase system were determined by GC-MS method.

modified alginate, starch, s5f, Lactobacillus amylovorus, D-/L-lactate, esters

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