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Employment of alginate-encapsulated Lactobacillus amylovorus DSM 201531T in production of lactates and their esters

Aim of this work is to create a set of optimal conditions for encapsulation of an amylolytic lactic acid bacterium together with a convenient polymeric substrate and thus enable direct conversion of the substrate to lactic acid by encapsulated biocatalyst. Formed capsules should meet certain specific requirements, as follows: (i) retain relative high metabolic activity of the biocatalyst in an isolated hydrocolloid environment, (ii) enable diffusion of produced lactic acid across a coating layer, and (iii) protect encapsulated biocatalyst from organic solvent and other unfavourable substances and conditions in exterior environment. Essentially uniform highly spherical modified calcium alginate beads with dimeter of 4.0 ± 02 mm containing amylolytic lactic acid bacterium Lactobacillus amylovorus DSM 20531T and high concentration of starch were prepared under aseptic conditions and used in batch experiments. First, metabolic activity of the entrapped biocatalyst was investigated in shaken flasks experiments at 45C, 150 rpm and decreasing mild acidic pH over three to four days. Utilization of starch from starch-loaded-beads by strain L. amylovorus DSM 20531T caused deformation of the beads and, later during the batch process, their disintegration, as expected. Simultaneous hydrolysis of starch to maltooligosaccharides, fermentation of maltooligosaccharides therefrom to D-/L-lactic acid and diffusion of the produced lactates to the exterior environment of the beads was identified and quantified by HPLC methods. Based on obtained experimental data it can be clearly concluded that the modified calcium alginate starch-loaded-beads fit completely the first two requirements. Then, influence of ethanol but also sulfuric acid in the exterior environment on persistence of rather soft and flexible beads under above described conditions was tested. Stable size, shape and color of the beads confirmed their endurance to both - ethanol and sulfuric acid when they were added separately and together to the liquid phase containing the beads. Therefore, the beads can serve as an efficient barrier between delicate beads interior and rather harsh environment. It remains to be experimentally proven if designed system can be used in manufacturing of lactate esters, e.g. ethyl lactate, outside of the beads. Up to now, we were able to quantify ethyl lactate formed in water-containing system at the level of mol/L by GC-MS method.

alginate beads, bacterial cells encapsulation, lactic acid, mass spectrometry-gas chromatography, starch

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