Advances in the understanding of the production, modification and applications of xylanases in the food industry.

Xylanases have broad applications in the food industry to decompose the complex carbohydrate xylan. This is applicable to enhance juice clarity, improve dough softness, or reduce beer turbidity. It can also be used to produce prebiotics and increase the nutritional value in foodstuff. However, the low yield and poor stability of most natural xylanases hinders their further applications. Therefore, it is imperative to explore higher-quality xylanases to address the potential challenges that appear in the food industry and to comprehensively improve the production, modification, and utilization of xylanases. Xylanases, due to their various sources, exhibit diverse characteristics that affect production and activity. Most fungi are suitable for solid-state fermentation to produce xylanases, but in liquid fermentation, microbial metabolism is more vigorous, resulting in higher yield. Fungi produce higher xylanase activity, but bacterial xylanases perform better than fungal ones under certain extreme conditions (high temperature, extreme pH). Gene and protein engineering technology helps to improve the production efficiency of xylanases and enhances their thermal stability and catalytic properties.

Secretion of Bacillus amyloliquefaciens Transglutaminase from Lactococcus lactis and Its Enhancement of Food Gel Properties.

(1) Background: Microbial transglutaminases (MTGase) catalyze protein crosslink. This is useful in the food industry to improve gelation, water holding capacity, and emulsifying capacity during foodstuff manufacturing. The production of MTGase in wild-type strains renders low yield and high costs of downstream purification, limiting its industrial applications. (2) Methods: In this work, MTGase from Bacillus amyloliquefaciens BH072 (BaMTGase) has been heterologously expressed in Lactococcus lactis, using the signal peptide Usp45 to direct the secretion of recombinant BaMTGase out of the cell for easier purification. (3) Results: In these conditions, MTGase was purified with a high yield (48.7 ± 0.2 mg/L) and high enzyme activity (28.6 ± 0.5 U/mg). Next, BaMTGase was tested for industrial applications. Recombinant BaMTGase and commercial MTGase were used for SPI solution crosslinking. BaMTGase formed a harder gel with higher water-holding capacity and a dense and smooth gel microstructure. (4) Conclusions: This work provides an attractive food-grade cell factory for the food industry and offers a suitable chassis for MTGase production.

Adsorption-Reaction Processes Between Gelatin and PDMS-E Emulsion Droplets.

In this work, the effects of droplet size and reaction time on the adsorption-reaction processes between gelatin and α-[3-(2,3-epoxypropoxy) propyl]-ω-butyl-polydimethylsiloxane (PDMS-E) emulsion droplets were studied. Gelatin molecules were only physically adsorbed on the surface of the PDMS-E droplet in the 0-75 min range, which was unrelated to the droplet size (100-1000 nm). For the small-size droplets (<410 nm), the physical adsorption proceeded over 75 min followed by agglomeration. For middle-size droplets (410-680 nm), the physical adsorption finished at 125 min; subsequently, the nucleophilic reaction between the primary amino group and the epoxy group began to happen, and globular-like or core-shell colloidal particles were formed. For large-size droplets (>680 nm), the nucleophilic reaction occurred at 75 min and produced core-shell or multi-layered colloidal particles. In a word, the physical absorption or nucleophilic reaction between gelatin and PDMS-E emulsion droplets could be controlled by controlling the droplet size and reaction time. Furthermore, the soft tissue paper coated with large-size droplets exhibited excellent resistance to water permeability and flame-resistant performance, which were carried out by water resistance and flammability tests.

The Secretion of Streptomyces monbaraensis Transglutaminase From Lactococcus lactis and Immobilization on Porous Magnetic Nanoparticles.

Microbial transglutaminase (MTG) from Streptomyces mobaraensis is an important enzyme widely applied in food processing for the improvement of protein properties by catalyzing the cross-linking of proteins. In this work we aimed at improving the production and enabling an easy and efficient purification process from culture supernatants. Thus, recombinant vectors, with either a constitutive promoter (P p5 ) or an inducible promoter (P nisA ), controlling the expression of the MTG gene fused to the signal peptide of Usp45 (SP usp45 ) were constructed and then expressed in Lactococcus lactis. After purification, 43.5 ± 0.4 mg/L mature MTG-6His was obtained. It displayed 27.6 ± 0.5 U/mg enzymatic activity cross-linking soy protein isolate effectively. The purified mature MTG was immobilized with magnetic porous Fe3O4 nanoparticles, which improved its activity up to 29.1 ± 0.4 U/mg. The immobilized MTG maintained 67.2% of the initial activity after being recycled for 10 times. The high production and secretion of functional S. mobaraensis MTG from L. lactis and the magnetic immobilized MTG-6His onto Fe3O4 nanoparticles reported in this study would have potential industrial applications.

Direct Growth of CNTs@CoSx Se2(1-x) on Carbon Cloth for Overall Water Splitting.

Searching for low-cost, high-efficiency, bifunctional, non-noble-metal electrocatalysts for overall water splitting is crucial to renewable energy conversion. Herein, a series of component-controllable CC/CNTs@CoSx Se2(1-x) (CC: carbon cloth, CNT: carbon nanotube) with excellent bifunctional properties in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were obtained by chemical vapor deposition. In this strategy, the Zif-67 precursor served as a structural inducer, which was directly grown on CC and pyrolyzed with the assistance of melamine to form multi-walled CNT-encapsulated CoSx Se2(1-x) hierarchical nanostructures. Subsequently, the electrocatalytic properties of the as-prepared materials were optimized by adjusting the S/Se molar ratio. Of note is that the lattice distortion caused by the different radii of Se and S generated a polarized electric field for easy adsorption of the intermediate products. The CoOOH generated in situ on the surface of CoSx Se2(1-x) , as well as n- and p-type domains in carbon, synergistically resulted in abundant active sites to boost the electrocatalytic activity. CC/CNTs@CoS0.74 Se0.52 exhibited overpotentials for the HER and OER of 225 and 285 mV, respectively and attained a current density of 10 mA cm-2 in alkaline solution. The as-prepared electrocatalysts could act as both cathode and anode in a water electrolyzer showing a cell voltage of 1.74 V and delivering 10 mA cm-2 , comparable to those of noble-metal-based water electrolyzers.