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

Characterization of an epilactose-producing cellobiose 2-epimerase from Clostridium sp. TW13 and reutilization of waste milk

A novel cellobiose 2-epimerase gene (CsCEase1) from Clostridium sp. TW13 was successfully overexpressed. CsCEase1, with a molecular weight of 45.0 kDa, exhibited a specific activity of 254.75 U/mg and showed optimal activity at 40 °C and pH 7.5. Using CsCEase1, 44.30 % of lactose was converted into epilactose, yielding a production level of 26.58 g/L. An efficient purification method was developed, incorporating crystallization and β-galactosidase treatment to remove the unconverted lactose, while Saccharomyces cerevisiae was used to consume the produced glucose. Final purification with activated carbon resulted in epilactose with 98 % purity and a recovery rate of 66.47 %. Furthermore, CsCEase1 was incubated with whey power and expired milk, achieving epilactose conversion rates of 29.65 % and 32.69 %, respectively. These findings highlight the potential of CsCEase1 for the cost-effective and environmentally sustainable production of epilactose from dairy waste.

Advances and prospects on production of lactulose and epilactose by cellobiose 2-epimerases: A review

Lactulose and epilactose are nondigestible disaccharides with a wide range of applications in clinical medicine, nutrition, and the food industry due to their health-benefiting properties. Their chemical synthesis typically involves stringent catalytic conditions and intricate reaction procedures, resulting in elevated production costs and challenges in product separation. Cellobiose 2-epimerases (CEs) facilitate the isomerization and epimerization of lactose to produce lactulose and epilactose directly, without the need for co-substrates. This enzymatic process offers advantages such as mild reaction conditions, straightforward operation, high conversion efficiency, and reduced by-product formation. Recently, numerous CE genes have been identified and characterized, with their enzymatic properties undergoing extensive analysis. This review consolidates information on the properties of CEs from various sources and examines their catalytic mechanisms based on crystal structure data. Additionally, the current research progress in the enzymatic synthesis of lactulose and epilactose is comprehensively reviewed. The future direction of CE research is discussed, highlighting the potential for large-scale production of lactulose and epilactose through environmentally sustainable enzymatic methods.

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.

Identification of a thermostable cellobiose 2-epimerase from Caldicellulosiruptor sp. Rt8.B8 and production of epilactose using Bacillus subtilis

BACKGROUND

Epilactose, a potential prebiotics, was derived from lactose through enzymatic catalysis. However, production and purification of epilactose are currently difficult due to powerless enzymes and inefficient downstream processing steps.

RESULTS

The encoding gene of cellobiose 2-epimerase (CE) from Caldicellulosiruptor sp. Rt8.B8 was cloned and expressed in Escherichia coli BL21(DE3). The enzyme was purified and it was suitable for industrial production of epilactose from lactose without by-products, because of high k_cat (197.6 s^-1 ) and preferable thermostability. The Rt8-CE gene was further expressed in the Bacillus subtilis strain. We successfully produced epilactose from 700 g L^-1 lactose in 30.4% yield by using the recombinant Bacillus subtilis whole cells. By screening of a β-galactosidase from Bacillus stearothermophilus (BsGal), a process for separating epilactose and lactose was established, which showed a purity of over 95% in a total yield of 69.2%. In addition, a mixed rare sugar syrup composed of epilactose and d-tagatose was successfully produced from lactose through the co-expression of l-arabinose isomerase and β-galactosidase.

CONCLUSION

Our study shed light on the efficient production of epilactose using a food-grade host expressing a novel CE enzyme. Moreover, an efficient and low-cost process was attempted to obtain high purity epilactose. In order to improve the utilization of raw materials, the production process of mixed syrup containing epilactose and d-tagatose with prebiotic properties produced from lactose was also established for the first time. © 2021 Society of Chemical Industry.

Efficient biosynthesis of exopolysaccharide from Jerusalem artichoke using a novel strain of Bacillus velezensis LT-2

This study focused on the non-grain biorefining of Jerusalem artichoke (JA) for exopolysaccharide (EPS) efficient production by using Bacillus velezensis LT-2. Results showed that LT-2 could directly utilize JA tuber power (JATP) for EPS production, and its EPS yield reached 11.47 ± 0.33 g/L in the simultaneous saccharification and fermentation (SSF) mode. Furthermore, the SSF mode shortened the fermentation period by 26.67% and reduced the fermentation cost by 79.41% due to the improved substrate utilization and the avoidance of inhibition effects of a high fructose concentration. Transcriptome sequencing results showed that inulin could accelerate nucleotide-sugars biosynthesis, induce EPS synthetic gene cluster transcription, and strengthen the electron transport respiratory chain and the transporter systems, thereby ensuring EPS efficient synthesis. This work exhibited a productive non-grain and environmentally friendly fermentation strategy for EPS biosynthesis, which promoted the JA industry development and created new prospects for high-value industrial products biosynthesis by using JATP.

Permeabilized TreS-Expressing Bacillus subtilis Cells Decorated with Glucose Isomerase and a Shell of ZIF-8 as a Reusable Biocatalyst for the Coproduction of Trehalose and Fructose

Metal-organic frameworks (MOFs) are a class of porous materials with versatile properties. In this study, ZIF-8 was employed to establish a two-enzyme system by encapsulating permeabilized Bacillus subtilis cells coated with glucose isomerase. B. subtilis was constructed by introducing the shuttle plasmid PMA5 associated with the overexpression of trehalose synthase. Using this two-enzyme system, trehalose was produced by trehalose synthase and the byproduct glucose was converted to fructose with the help of glucose isomerase. The decrease in glucose production not only relieved the inhibition of the entire reaction chain but also increased the final yield of trehalose. The highest trehalose production rate reached 67.7% and remained above 50% after 20 batches. In addition, the toxicity of the ZIF-8 coating for B. subtilis was investigated by fluorescence microscopy and was found to be negligible. By simulating an extreme environment, the ZIF-8 coating was demonstrated to have a protective effect on the cells and enzymes. This study provides a theoretical basis for the application of MOFs in the immobilization of microorganisms and enzymes.

Sustainable Valorization of Whey by Electroactivation Technology for In Situ Isomerization of Lactose into Lactulose: Comparison between Electroactivation and Chemical Processes at Equivalent Solution Alkalinity

The demand for production of prebiotics at a commercial scale is rising due to the consumers' growing health awareness. Whey, a coproduct of the dairy industries, is a suitable feed medium to produce a prebiotic lactulose through the isomerization of lactose under alkaline conditions. The aim of the present study was to compare the isomerization of lactose into lactulose in situ of whey by using electroactivation technology with the chemical isomerization method using KOH as catalysis under equivalent solution alkalinity. Electroisomerization of lactose into lactulose was performed by using whey solutions of 7, 14, and 21% (w/v) dry matter under current intensities of 300, 600, and 900 mA, respectively, during 60 min with a sampling interval of 5 min. The conventional chemical method was carried out using KOH powder as catalyst at the alkalinity that corresponded to that measured in the electroactivated whey at each 5 min interval. The results showed that lactulose production was dependent on the whey concentration, current intensity, and EA time. The highest lactulose yield of 32% was achieved under a 900 mA current intensity at 60 min for a 7% whey solution. Thereafter, the EA conditions were compared to those of a conventional chemical isomerization process by maintaining similar alkalinity in the feed solutions. However, no lactulose was produced by the chemical process for the equivalent solution alkalinity as in the EA technique. These results were correlated with the solution pH, which reached the required values in a 7% whey solution with values of up to pH 11.50, whereas the maximum pH values that were obtained at higher whey concentrations were around 10-10.50, which was not enough to initiate the lactose isomerization reaction. The outcomes of this study suggest that EA is an efficient technology to produce lactulose using whey lactose.

Insights into Thermophilic Plant Biomass Hydrolysis from Caldicellulosiruptor Systems Biology

Plant polysaccharides continue to serve as a promising feedstock for bioproduct fermentation. However, the recalcitrant nature of plant biomass requires certain key enzymes, including cellobiohydrolases, for efficient solubilization of polysaccharides. Thermostable carbohydrate-active enzymes are sought for their stability and tolerance to other process parameters. Plant biomass degrading microbes found in biotopes like geothermally heated water sources, compost piles, and thermophilic digesters are a common source of thermostable enzymes. While traditional thermophilic enzyme discovery first focused on microbe isolation followed by functional characterization, metagenomic sequences are negating the initial need for species isolation. Here, we summarize the current state of knowledge about the extremely thermophilic genus Caldicellulosiruptor, including genomic and metagenomic analyses in addition to recent breakthroughs in enzymology and genetic manipulation of the genus. Ten years after completing the first Caldicellulosiruptor genome sequence, the tools required for systems biology of this non-model environmental microorganism are in place.

Simulation-guided enzyme discovery: A new microbial source of cellobiose 2-epimerase

Cellobiose 2-epimerase (CE) is a promising industrial enzyme that can be utilized in the dairy industry. More thermostable CEs from different microorganisms are still needed for a higher lactulose productivity. This study demonstrated the feasibility to use molecular dynamics (MD) simulation as the preliminary computational filter for thermostable enzymes screening. Sequence information of eleven uncharacterized CEs were chosen to be analyzed by MD simulations. The CE from Dictyoglomus thermophilum (Dith-CE) was determined experimentally to be one of the most thermostable CEs with the highest epimerization (160 ± 6.5 U mg^-1) and isomerization activities (3.52 ± 0.23 U mg^-1) among all the reported CEs. This enzyme shows the highest isomerization activity at 85 °C and pH 7.0. The kinetic parameters (k_cat and K_m) of isomerization activity of this CE are 3.98 ± 0.3 s^-1 and 235.2 ± 11.2 mM, respectively. These results suggest that the CE from Dith-CE is a promising lactulose-producing enzyme.

Sustainable bioconversion of food waste into high-value products by immobilized enzymes to meet bio-economy challenges and opportunities - A review

Over the past few years, food waste has intensified much attention from the local public, national and international organizations as well as a wider household territory due to increasing environmental, social and economic concerns, climate change and scarcity of fossil fuel resources. On one aspect, food-processing waste represents a substantial ecological burden. On the other hand, these waste streams are rich in carbohydrates, proteins, and lipids, thus hold significant potential for biotransformation into an array of high-value compounds. Indeed, the high sugar, protein, and fat content render food waste streams as attractive feedstocks for enzymatic valorization given the plentiful volumes generated annually. Enzymes as industrial biocatalysts offer unique advantages over traditional chemical processes with regard to eco-sustainability, and process efficiency. Herein, an effort has been made to delineate immobilized enzyme-driven valorization of food waste streams into marketable products such as biofuels, bioactive compounds, biodegradable plastics, prebiotics, sweeteners, rare sugars, surfactants, etc. Current challenges and prospects are also highlighted with respect to the development of industrially adaptable biocatalytic systems to achieve the ultimate objectives of sustainable manufacturing combined with minimum waste generation. Applications-based strategies to enzyme immobilization are imperative to design cost-efficient and sustainable industrially applicable biocatalysts. With a deeper apprehension of support material influences, and analyzing the extreme environment, enzymes might have significant potential in improving the overall sustainability of food processing.

Development of sugarcane resource for efficient fermentation of exopolysaccharide by using a novel strain of Kosakonia cowanii LT-1

This work focuses on the development of non-food fermentation for the cost-effective biosynthesis of exopolysaccharide (EPS) by using a new strain of Kosakonia cowanii LT-1. This novel strain more efficiently utilizes sucrose for EPS production than other glycosyl donors. Comparative transcriptomic analysis is used to understand EPS synthesis promotion and the effects of sucrose on EPS biosynthesis. We speculate that ATP-binding cassette transporter, phosphotransferase, and two-component systems may be the most essential factors for EPS biosynthesis. The enhanced oxidative phosphorylation increases the synthesis rate of ATP to satisfy the energy demands for EPS production with sucrose as the substrate. Sugarcane juice, a cheap raw material, could improve the EPS yield in batch fermentation and achieve approximately 29.66% cost savings for substrate. Our work presents a promising non-food fermentation approach for the synthesis of high-value industrial products.

Continuous enzymatic synthesis of lactulose in packed-bed reactor with immobilized Aspergillus oryzae β-galactosidase

Lactulose synthesis from fructose and lactose in continuous packed-bed reactor operation with glyoxyl-agarose immobilized Aspergillus oryzae β-galactosidase is reported for the first time. Alternative strategies to conventional batch synthesis have been scarcely explored for lactulose synthesis. The effect of flow rate, substrates ratio and biocatalyst-inert packing material mass ratio (M_B/M_IM) were studied on reactor performance. Increase in any of these variables produced an increase in lactulose yield (Y_Lu) being higher than obtained in batch synthesis at comparable conditions. Maximum Y_Lu of 0.6 g·g^-1 was obtained at 50 °C, pH 4.5, 50% w/w total sugars, 15 mL·min^-1, fructose/lactose molar ratio of 12 and M_B/M_IM of 1/8 g·g^-1; at such conditions yield of transgalactosylated oligosaccharides (Y_TOS) was 0.16 g·g^-1, selectivity (lactulose/TOS molar ratio) was 5.4 and lactose conversion (X_Lactose) was 28%. Reactor operation with recycle had no significant effect on yield, producing only some decrease in productivity.

Converting Galactose into the Rare Sugar Talose with Cellobiose 2-Epimerase as Biocatalyst

Cellobiose 2-epimerase from Rhodothermus marinus (RmCE) reversibly converts a glucose residue to a mannose residue at the reducing end of β-1,4-linked oligosaccharides. In this study, the monosaccharide specificity of RmCE has been mapped and the synthesis of d-talose from d-galactose was discovered, a reaction not yet known to occur in nature. Moreover, the conversion is industrially relevant, as talose and its derivatives have been reported to possess important antimicrobial and anti-inflammatory properties. As the enzyme also catalyzes the keto-aldo isomerization of galactose to tagatose as a minor side reaction, the purity of talose was found to decrease over time. After process optimization, 23 g/L of talose could be obtained with a product purity of 86% and a yield of 8.5% (starting from 4 g (24 mmol) of galactose). However, higher purities and concentrations can be reached by decreasing and increasing the reaction time, respectively. In addition, two engineering attempts have also been performed. First, a mutant library of RmCE was created to try and increase the activity on monosaccharide substrates. Next, two residues from RmCE were introduced in the cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) (S99M/Q371F), increasing the k_cat twofold.