CE-UV/VIS and CE-MS for monitoring organic impurities during the downstream processing of fermentative-produced lactic acid from second-generation renewable feedstocks

Abstract

BackgroundDuring the downstream process of bio-based bulk chemicals, organic impurities, mostly residues from the fermentation process, must be separated to obtain a pure and ready-to-market chemical. In this study, capillary electrophoresis was investigated for the non-targeting downstream process monitoring of organic impurities and simultaneous quantitative detection of lactic acid during the purification process of fermentatively produced lactic acid. The downstream process incorporated 11 separation units, ranging from filtration, adsorption and ion exchange to electrodialysis and distillation, and 15 different second-generation renewable feedstocks were processed into lactic acid. The identification of organic impurities was established through spiking and the utilization of an advanced capillary electrophoresis mass spectrometry system.ResultsA total of 53 % of the organic impurities were efficiently removed via bipolar electrodialysis; however, one impurity, pyroglutamic acid, was recalcitrant to separation. It was demonstrated that the presence of pyroglutamic acid disrupts the polymerization of lactic acid into poly lactic acid. Pyroglutamic acid was present in all lactic acid solutions, independent of the type of renewable resource or the bacterium applied. Pyroglutamic acid, also known as 5-oxoproline, is a metabolite in the glutathione cycle, which is present in all living microorganisms. pyroglutamic acid is found in many proteins, and during intracellular protein metabolism, N-terminal glutamic acid and glutamine residues can spontaneously cyclize to become pyroglutamic acid. Hence, the concentration of pyroglutamic acid in the lactic acid solution can only be limited to a certain amount.ConclusionsThe present study proved the capillary electrophoresis system to be an important tool for downstream process monitoring. The high product concentration encountered in biological production processes did not hinder the capillary electrophoresis from separating and detecting organic impurities, even at minor concentrations. The coupling of the capillary electrophoresis with a mass spectrometry system allowed for the straightforward identification of the remaining critical impurity, pyroglutamic acid. Although 11 separation units were applied during the downstream process, the pyroglutamic acid concentration remained at 12,900 ppm, which was comparatively high. All organic impurities found were tracked by the capillary electrophoresis, allowing for further separation optimization.Electronic supplementary materialThe online version of this article (doi:10.1186/s13036-016-0027-2) contains supplementary material, which is available to authorized users.

Recent advances in the application of capillary electromigration methods for food analysis and Foodomics

“…Besides, CE‐UV has been employed for the determination of the organic acids composition and quantification of 31 wine samples and for the classification of 38 samples of commercial wine from four wine‐producing provinces of Argentina according to the grape variety applying the Tucker3 algorithm , as well as for the measure of the changes in organic acids levels in coffee seeds as function of different fermentation treatments . Moreover, CE has shown an interesting application as a tool for the downstream process monitoring by the detection of organic impurities in the process of lactic acid purification from 15‐s generation renewable feedstock .…”

Investigation of spiral-wound membrane modules for the cross-flow nanofiltration of fermentation broth obtained from a pilot plant fermentation reactor for the continuous production of lactic acid

“…Additional file 1: Figure S2 (see supporting information) shows the electropherograms generated by the CE system of the media permeate for the membranes and the feed (Laube et al 2016). The electropherograms portray the rejection characteristic of the organic molecule fractions in the permeate.…”

“…The direct detection mode micellar electrokinetic chromatography (MEKC) was applied. The detection wavelength and bandwidth were each 200 nm (Laube et al 2016). …”

“…The permeate has a medium sodium lactate (57,000 ppm) and a low macromolecule concentration. The retentate has a low sodium lactate (35,300 ppm) and a high macromolecule concentration (Laube et al 2016a). The retentate, in the case of the continuous process, is either recycled back to the fermenter, along with the LA bacteria, or forwarded to another membrane separator (Kamm et al 2008).…”

Conceptual design of a dual reactive dividing wall column for downstream processing of lactic acid

“…In contrast, process simulation experiments use mixtures of LA and water only, in some cases also adding inert impurities. Laube et al (2016) studied the purification of LA experimentally from fermentation broths with impurities. As a result, a 15-unit operation process without reaction was produced, which did not effectively remove pyroglutamic acid, which is undesirable, especially for LA polymerisation into PLA.…”