Bioproduction and applications of aldobionic acids with a focus on maltobionic and cellobionic acid

Cellobionate production from sodium hydroxide pretreated wheat straw by engineered Neurospora crassa HL10

This study investigated cellobionate production from a lignocellulosic substrate using Neurospora crassa HL10. Utilizing NaOH-pretreated wheat straw as the substrate obviated the need for an exogenous redox mediator addition, as lignin contained in the pretreated wheat served as a natural mediator. The low laccase production by N. crassa HL10 on pretreated wheat straw caused slow cellobionate production, and exogenous laccase addition accelerated the process. Cycloheximide induced substantial laccase production in N. crassa HL10, enabling the strain to yield approximately 57 mM cellobionate from pretreated wheat straw (equivalent to 20 g/L cellulose), shortening the conversion time from 8 to 6 days. About 92% of the cellulose contained in the pretreated wheat straw is converted to cellobionate. In contrast to existing methods requiring pure cellobiose or cellulase enzymes, this process efficiently converts a low-cost feedstock into cellobionate at a high yield without enzyme or redox mediator supplementation.

Recombinant cellobiose dehydrogenase from Thermothelomyces thermophilus: Its functional characterization and applicability in cellobionic acid production

The fungus Thermothelomyces thermophilus is a thermotolerant microorganism that has been explored as a reservoir for enzymes (hydrolytic enzymes and oxidoreductases). The functional analysis of a recombinant cellobiose dehydrogenase (MtCDHB) from T. thermophilus demonstrated a thermophilic behavior, an optimal pH in alkaline conditions for inter-domain electron transfer, and catalytic activity on cellooligosaccharides with different degree of polymerization. Its applicability was evaluated to the sustainable production of cellobionic acid (CBA), a potential pharmaceutical and cosmetic ingredient rarely commercialized. Dissolving pulp was used as a disaccharide source for MtCDHB. Initially, recombinant exoglucanases (MtCBHI and MtCBHII) from T. thermophilus hydrolyzed the dissolving pulp, resulting in 87% cellobiose yield, which was subsequently converted into CBA by MtCDHB, achieving a 66% CBA yield after 24 h. These findings highlight the potential of MtCDHB as a novel approach to obtaining CBA through the bioconversion of a plant-based source.

Sustainable cellobionic acid biosynthesis from starch via artificial in vitro synthetic enzymatic biosystem

Cellobionic acid (CBA), a kind of aldobionic acid, offers potential applications in the fields of pharmaceutical, cosmetic, food, and chemical industry. To tackle the high cost of the substrate cellobiose in CBA production using quinoprotein glucose dehydrogenase, this study developed a coenzyme-free and phosphate-balanced in vitro synthetic enzymatic biosystem (ivSEBS) to enable the sustainable CBA synthesis from cost-effective starch in one-pot via the CBA-synthesis module and gluconic acid-supply module. The metabolic fluxes of this artificial biosystem were strengthened using design-build-test-analysis strategy, which involved exquisite pathway design, meticulous enzyme selection, module validation and integration, and optimization of the key enzyme dosage. Under the optimized conditions, a remarkable concentration of 6.2 g/L CBA was achieved from initial 10 g/L maltodextrin with a starch-to-CBA molar conversion rate of 60 %. Taking into account that the biosystem simultaneously accumulated 3.6 g/L of gluconic acid, the maltodextrin utilization rate was calculated to be 93.3 %. Furthermore, a straightforward scaling-up process was performed to evaluate the industrial potential of this enzymatic biosystem, resulting in a yield of 21.2 g/L CBA from 50 g/L maltodextrin. This study presents an artificial ivSEBS for sustainable production of CBA from inexpensive starch, demonstrating an alternative paradigm for biomanufacturing of other aldobionic acids.

Purification, bioactivity and application of maltobionic acid in active films

The objective of this study was to purify sodium maltobionate using Zymomonas mobilis cells immobilized in situ on flexible polyurethane (PU) and convert it into maltobionic acid for further evaluation of bioactivity (iron chelating ability, antibacterial potential and cytoprotection) and incorporation into films based on cassava starch, chitosan, and cellulose acetate. Sodium maltobionate exhibited a purity of 98.1% and demonstrated an iron chelating ability of approximately 50% at concentrations ranging from 15 to 20 mg mL-1. Maltobionic acid displayed minimal inhibitory concentrations (MIC) of 8.5, 10.5, 8.0, and 8.0 mg mL-1 for Salmonella enterica serovar Choleraesuis, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes, respectively. Maltobionic acid did not exhibit cytotoxicity in HEK-293 cells at concentrations up to 500 µg mL-1. Films incorporating 7.5% maltobionic acid into cassava starch and chitosan demonstrated inhibition of microbial growth, with halo sizes ranging from 15.67 to 22.33 mm. These films had a thickness of 0.17 and 0.13 mm, water solubility of 62.68% and 78.85%, and oil solubility of 6.23% and 11.91%, respectively. The cellulose acetate film exhibited a non-uniform visual appearance due to the low solubility of maltobionic acid in acetone. Mechanical and optical properties were enhanced with the addition of maltobionic acid to chitosan and cassava films. The chitosan film with 7.5% maltobionic acid demonstrated higher tensile strength (30.3 MPa) and elongation at break (9.0%). In contrast, the cassava starch film exhibited a high elastic modulus (1.7). Overall, maltobionic acid, with its antibacterial activity, holds promise for applications in active films suitable for food packaging.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03879-3.