Continuous hydrolysis of pullulan using covalently immobilized pullulanase in a packed bed reactor

Exploring the potential of pullulan-based films and coatings for effective food preservation: A comprehensive analysis of properties, activation strategies and applications

Pullulan is naturally occurring polysaccharide exhibited potential applications for food preservation has gained increasing attention over the last half-century. Recent studies focused on efficient preservation and targeted inhibition using active composite ingredients and advanced technologies. This has led to the emergence of pullulan-based biofilm preservation. This review extensively studied the characteristics of pullulan-based films and coatings, including their mechanical strength, water vapor permeability, thermal stability, and potential as a microbial agent. Furthermore, the distinct characteristics of pullulan, production methods, and activation strategies, such as pullulan derivatization, various compounded ingredients (plant extracts, microorganisms, and animal additives), and other technologies (e.g., ultrasound), are thoroughly studied for the functional property enhancement of pullulan-based films and coatings, ensuring optimal preservation conditions for diverse food products. Additionally, we explore hypotheses that further illuminate pullulan's potential as an eco-friendly bioactive material for food packaging applications. In addition, this review evaluates various methods to improve the efficiency of the film-forming mechanism, such as improving the direct coating process, bioactive packaging films, and implementing layer-by-layer coatings. Finally, current analyses put forward suggestions for future advancement in pullulan-based bioactive films, with the aim of expanding their range of potential applications.

The application of conventional or magnetic materials to support immobilization of amylolytic enzymes for batch and continuous operation of starch hydrolysis processes

In the production of ethanol, starches are converted into reducing sugars by liquefaction and saccharification processes, which mainly use soluble amylases. These processes are considered wasteful operations as operations to recover the enzymes are not practical economically so immobilizations of amylases to perform both processes appear to be a promising way to obtain more stable and reusable enzymes, to lower costs of enzymatic conversions, and to reduce enzymes degradation/contamination. Although many reviews on enzyme immobilizations are found, they only discuss immobilizations of α-amylase immobilizations on nanoparticles, but other amylases and support types are not well informed or poorly stated. As the knowledge of the developed supports for most amylase immobilizations being used in starch hydrolysis is important, a review describing about their preparations, characteristics, and applications is herewith presented. Based on the results, two major groups were discovered in the last 20 years, which include conventional and magnetic-based supports. Furthermore, several strategies for preparation and immobilization processes, which are more advanced than the previous generation, were also revealed. Although most of the starch hydrolysis processes were conducted in batches, opportunities to develop continuous reactors are offered. However, the continuous operations are difficult to be employed by magnetic-based amylases.

Regulation of the catalytic behavior of pullulanases chelated onto nickel (II)-modified magnetic nanoparticles

Chelating of pullulanases onto nickel (II)-modified magnetic nanoparticles results in one-step purification and immobilization of pullulanase, and facilitates the commercial application of pullulanase in industrial scale. To improve the catalytic behavior, especially the operational stability, of the nanocatalyst in consecutive batch reactions, we prepared various iminodiacetic acid-modified magnetic nanoparticles differed in surface polarity and spacer length, on which the His6-tagged pullulanases were chelated via nickel ions, and then studied the correlation between the MNPs surface property and the corresponding catalyst behavior. When pullulanases were chelated onto the surface-modified MNPs, the thermostability of all pullulanase derivatives were lower than that of free counterpart, being not relevant to the protein orientation guided by the locality of the His6-tag, but related to the MNPs basal surface polarity and the grafted spacer length. After chelating of pullulanases onto MNPs, there were changes observed in the pH-activity profile and the apparent Michaelis constant toward pullulan. The changing tendencies were mainly dependent on the His6-tagged pullulanase orientation, and the changing extents were tuned by the spacer length. The reusability of pullulanase immobilized by N-terminal His6-tag was higher than that of pullulanase immobilized by C-terminal His6-tag. Moreover, the reusability of the immobilized pullulanase tested increased till grafting polyether amine-400 as spacer-arm, therefore the N-terminal His6-tagged pullulanase chelating MNPs grafted polyether amine-400 gave the best reusability, which retained 60% of initial activity after 18 consecutive cycles with a total reaction time of 9h. Additionally, the correlation analysis of the catalyst behaviors indicated that the reusability was independent from other catalytic properties such as thermostability and substrate affinity. All the results revealed that the catalyst behavior can be mainly controlled by the His6-tagged pullulanase orientation than by the MNPs surface property which can tune the catalyst function.

Depiction of carbohydrate-active enzyme diversity in Caldicellulosiruptor sp. F32 at the genome level reveals insights into distinct polysaccharide degradation features

Diverse and distinctive encoding sequences of CAZyme in the genome of Caldicellulosiruptor sp. F32 enable the deconstruction of unpretreated lignocellulose.

High-level expression of Bacillus naganoensis pullulanase from recombinant Escherichia coli with auto-induction: effect of lac operator

Pullulanase plays an important role in specific hydrolysis of branch points in amylopectin and is generally employed as an important enzyme in starch-processing industry. So far, however, the production level of pullulanase is still somewhat low from wide-type strains and even heterologous expression systems. Here the gene encoding Bacillus naganoensis pullulanase was amplified and cloned. For expression of the protein, two recombinant systems, Escherichia coli BL21(DE3)/pET-20b(+)-pul and E. coli BL21(DE3)/pET-22b(+)-pul, were constructed, both bearing T7 promoter and signal peptide sequence, but different in the existance of lac operator and lacI gene encoding lac repressor. Recombinant pullulanase was initially expressed with the activity of up to 14 U/mL by E. coli BL21(DE3)/pET-20b(+)-pul with IPTG induction in LB medium, but its expression level reduced continually with the extension of cryopreservation time and basal expression was observed. However, E. coli BL21(DE3)/pET-22b(+)-pul , involving lac operator downstream of T7 promoter to regulate foreign gene transcription, exhibited pullulanase activity consistently without detected basal expression. By investigating the effect of lac operator, basal expression of foreign protein was found to cause expression instability and negative effect on production of target protein. Thus double-repression strategy was proposed that lac operators in both chromosome and plasmid were bound with lac repressor to repress T7 RNA polymerase synthesis and target protein expression before induction. Consequently, the total activity of pullulanase was remarkably increased to 580 U/mL with auto-induction by lac operator-involved E. coli BL21(DE3)/pET-22b(+)-pul. When adding 0.6% glycine in culture, the extracellular production of pullulanase was significantly improved with the extracellular activity of 502 U/mL, which is a relatively higher level achieved to date for extracellular production of pullulanase. The successful expression of pullulanase with lac operator regulation provides an efficient way for enhancement of expression stability and hence high-level production of target protein in recombinant E. coli.

Use of polyhydroxybutyrate and ethyl cellulose for coating of urea granules

Fertilizers contain essential nutrients for agricultural growth and development. However, most nitrogen fertilizers are substances with high solubility of ions and are very susceptible to leaching and volatilization. To minimize these losses, an alternative is the creation of a physical barrier around granules. One way is to coat granules with polymers. In the present work urea granules were coated with polyhydroxybutyrate and ethyl cellulose in various conditions in the presence of emulsifiers. The original granules and the final products were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetry, to evaluate the surface morphology, the interaction between the granules and the coating, and the rates of mass change. The rates of urea release in distilled water were measured with a commercial enzyme kit. It is shown that those polymers are effective for coating of granules, leading to reduction of rates of urea dissolution in water.

Signal peptide-independent secretory expression and characterization of pullulanase from a newly isolated Klebsiella variicola SHN-1 in Escherichia coli

A strain with the power to produce extracellular pullulanase was obtained from the sample taken from a flour mill. By sequencing its 16S rDNA, the isolate was identified as Klebsiella variicola SHN-1. When the gene encoding pullulanase, containing the N-terminal signal sequence, was cloned into Escherichia coli BL21 (DE3), extracellular activity was detected up to 10 U/ml, a higher level compared with the results in published literature. Subsequently, the recombinant pullulanase was purified and characterized. The main end product from pullulan hydrolyzed by recombinant pullulanase was determined as maltotriose with HPLC, and hence, the recombinant pullulanase was identified as type I pullulanase, which could be efficiently employed in starch processing to produce maltotriose with higher purity and even to evaluate the purity of pullulan. To investigate the effect of signal peptide on secretion of the recombinant enzyme, the signal sequence was removed from the constructed vector. However, secretion of pullulanase in E. coli was not influenced, which was seldom reported previously. By localizing the distribution of pullulanase on subcellular fractions, the secretion of recombinant pullulanase in E. coli BL21 (DE3) was confirmed, even from the expression system of nonsecretory type without the assistance of signal peptide.

Continuous-flow step gradient mass spectrometry based method for the determination of kinetic parameters of immobilized mushroom tyrosinase in equilibrating conditions: comparison with free enzyme

A mass spectrometry (MS)-based methodology for enzymatic assay in equilibrium conditions was designed and evaluated. This on-line assay involves the introduction of a continuous-flow step gradient (CFSG) of a substrate solution in the column containing immobilized enzyme and the simultaneous tracking of the product formation. We showed that the constant concentration of substrate in the entire bioreactor for an appropriate duration ensures the equilibration of the studied enzyme (mushroom tyrosinase). Under these conditions, it was demonstrated also that the kinetic and enzymatic parameters (Michaelis-Menten constant, K(M) , the maximal specific activity, SA(max)) are independent of the flow rate of the mobile phase. The feasibility of the mentioned approach for inhibitory tests was also investigated. The coupling of the mass spectrometer to the bio-reactor allows the selective monitoring of the enzymatic reaction products and increases their detection level. Very high sensitivity, 500 pmol/min/column, and selective monitoring of the products of the enzymatic reaction are allowed by MS detection. The methodology developed here constitutes a sensitive analytical tool to study enzymes requiring long equilibration times.