Lactulose production from lactose by recombinant cellobiose 2-epimerase in permeabilisedEscherichia colicells

Production of lactulose from lactose using a novel cellobiose 2-epimerase from Clostridium disporicum

Lactulose is a semisynthetic nondigestive sugar derived from lactose, with wide applications in the food and pharmaceutical industries. Its biological production routes which use cellobiose 2-epimerase (C2E) as the key enzyme have attracted widespread attention. In this study, a set of C2Es from different sources were overexpressed in Escherichia coli to produce lactulose. We obtained a novel and highly efficient C2E from Clostridium disporicum (CDC2E) to synthesize lactulose from lactose. The effects of different heat treatment conditions, reaction pH, reaction temperature, and substrate concentrations were investigated. Under the optimum biotransformation conditions, the final concentration of lactulose was up to 1.45 M (496.3 g/L), with a lactose conversion rate of 72.5 %. This study provides a novel C2E for the biosynthesis of lactulose from low-cost lactose.

Lactulose production from lactose isomerization by chemo-catalysts and enzymes: Current status and future perspectives

Lactulose, a semisynthetic nondigestive disaccharide with versatile applications in the food and pharmaceutical industries, has received increasing interest due to its significant health-promoting effects. Currently, industrial lactulose production is exclusively carried out by chemical isomerization of lactose via the Lobry de Bruyn-Alberda van Ekenstein (LA) rearrangement, and much work has been directed toward improving the conversion efficiency in terms of lactulose yield and purity by using new chemo-catalysts and integrated catalytic-purification systems. Lactulose can also be produced by an enzymatic route offering a potentially greener alternative to chemo-catalysis with fewer side products. Compared to the controlled trans-galactosylation by β-galactosidase, directed isomerization of lactose with high isomerization efficiency catalyzed by the most efficient lactulose-producing enzyme, cellobiose 2-epimerase (CE), has gained much attention in recent decades. To further facilitate the industrial translation of CE-based lactulose biotransformation, numerous studies have been reported on improving biocatalytic performance through enzyme mediated molecular modification. This review summarizes recent developments in the chemical and enzymatic production of lactulose. Related catalytic mechanisms are also highlighted and described in detail. Emerging techniques that aimed at advancing lactulose production, such as the boronate affinity-based technique and molecular biological techniques, are reviewed. Finally, perspectives on challenges and opportunities in lactulose production and purification are also discussed.

Potential of Biocatalysis in Pharmaceuticals

Biocatalysis has been continuously evolving as an essential tool which is playing a significant role in the industrial synthesis of chemicals, active pharmaceuticals, pharmaceutical intermediates, etc. where the high-yielding chemo-, regio-, and enantioselective reactions are needed. Despite its vital importance, industrial biocatalysis is facing certain limitations such as operational stability, economic viability, efficient recovery, and reusability. The limitations mentioned can be overcome by the isolation of specific enzyme producers from extreme environment by protein engineering, bioinformatics, and recombinant DNA technologies. Recently, chemoenzymatic pathway and biological cascade reactions have also been developed and designed to perform the synthesis of pharmaceuticals. In this chapter, we compile the broad applications of biocatalysts in the synthesis of pharmaceuticals.

Characterisation of a novel cellobiose 2-epimerase from thermophilic Caldicellulosiruptor obsidiansis for lactulose production

BACKGROUND

Lactulose, a bioactive lactose derivative, has been widely used in food and pharmaceutical industries. Isomerisation of lactose to lactulose by cellobiose 2-epimerase (CE) has recently attracted increasing attention, since CE produces lactulose with high yield from lactose as a single substrate. In this study, a new lactulose-producing CE from Caldicellulosiruptor obsidiansis was extensively characterised.

RESULTS

The recombinant enzyme exhibited maximal activity at pH 7.5 and 70 °C. It displayed high thermostability with T_m of 86.7 °C. The half-life was calculated to be 8.1, 2.8 and 0.6 h at 75, 80, and 85 °C, respectively. When lactose was used as substrate, epilactose was rapidly produced in a short period, and afterwards both epilactose and lactose were steadily isomerised to lactulose, with a final ratio of 35:11:54 for lactose:epilactose:lactulose. When the reverse reaction was investigated using lactulose as substrate, both lactose and epilactose appeared to be steadily produced from the start.

CONCLUSION

The recombinant CE showed both epimerisation and isomerisation activities against lactose, making it an alternative promising biocatalyst candidate for lactulose production. © 2016 Society of Chemical Industry.

Efficient production of lactulose from whey powder by cellobiose 2-epimerase in an enzymatic membrane reactor

In this study, the gene encoding cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) was successfully expressed in Bacillus subtilis WB800. After the fermentation medium optimization, the activity of recombinant strain was 4.5-fold higher than the original medium in a 7.5L fermentor. The optimal catalytic pH and temperature of crude CsCE were 7.0 and 80°C, respectively. An enzymatic synthesis of lactulose was developed using cheese-whey lactose as its substrate. The maximum conversion rate of whey powder obtained was 58.5% using 7.5 U/mL CsCE. The enzymatic membrane reactor system exhibited a great operational stability, confirmed with the higher lactose conversion (42.4%) after 10 batches. To our best knowledge, this is the first report of lactulose synthesis in food grade strain, which improve the food safety, and we not only realize the biological production of lactulose, but also make good use of industrial waste, which have positive impact on environment.

Hidden Reaction: Mesophilic Cellobiose 2-Epimerases Produce Lactulose

Lactulose (4-O-β-d-galactopyranosyl-d-fructofuranose) is a prebiotic sugar derived from the milk sugar lactose (4-O-β-d-galactopyranosyl-d-glucopyranose). In our study we observed for the first time that known cellobiose 2-epimerases (CEs; EC 5.1.3.11) from mesophilic microorganisms were generally able to catalyze the isomerization reaction of lactose into lactulose. Commonly, CEs catalyze the C2-epimerization of d-glucose and d-mannose moieties at the reducing end of β-1,4-glycosidic-linked oligosaccharides. Thus, epilactose (4-O-β-d-galactopyranosyl-d-mannopyranose) is formed with lactose as substrate. So far, only four CEs, exclusively from thermophilic microorganisms, have been reported to additionally catalyze the isomerization reaction of lactose into lactulose. The specific isomerization activity of the seven CEs in this study ranged between 8.7 ± 0.1 and 1300 ± 37 pkat/mg. The results indicate that very likely all CEs are able to catalyze both the epimerization as well as the isomerization reaction, whereby the latter is performed at a comparatively much lower reaction rate.

Synthesis and purification of galacto-oligosaccharides: state of the art

Lactose-derived non-digestible oligosaccharides are prominent components of functional foods. Among them, galacto-oligosaccharides (GOS) outstand for being prebiotics whose health-promoting effects are supported on strong scientific evidences, having unique properties as substitutes of human milk oligosaccharides in formulas for newborns and infants. GOS are currently produced enzymatically in a kinetically-controlled reaction of lactose transgalactosylation catalyzed by β-galactosidases from different microbial strains. The enzymatic synthesis of GOS, although being an established technology, still offers many technological challenges and opportunities for further development that has to be considered within the framework of functional foods which is the most rapidly expanding market within the food sector. This paper presents the current technological status of GOS production, its main achievements and challenges. Most of the problems yet to be solved refer to the rather low GOS yields attainable that rarely exceed 40 %, corresponding to lactose conversions around 60 %. This means that the product or reaction (raw GOS) contains significant amounts of residual lactose and monosaccharides (glucose and galactose). Efforts to increase such yields have been for the most part unsuccessful, even though improvements by genetic and protein engineering strategies are to be expected in the near future. Low yields impose a burden on downstream processing to obtain a GOS product of the required purity. Different strategies for raw GOS purification are reviewed and their technological significance is appraised.