Enhancement of ß-Cyclodextrin Production Using a Glycogen Debranching Enzyme from Saccharolobus solfataricus STB09.

Efficient production of cyclodextrins (CDs) has always been challenging. CDs are primarily produced from starch via cyclodextrin glycosyltransferase (CGTase), which acts on α-1,4 glucosidic bonds; however, α-1,6 glucosidic bonds in starch suppress the enzymatic production of CDs. In this study, a glycogen debranching enzyme from Saccharolobus solfataricus STB09 (SsGDE) was utilized to promote the production of ß-CD by hydrolyzing α-1,6 glucosidic bonds. The addition of SsGDE (750 U/g of starch) at the liquefaction stage remarkably improved the ß-CD yield, with a 43.9% increase. Further mechanism exploration revealed that SsGDE addition could hydrolyze specific branches with less generation of byproducts, thereby promoting CD production. The chain segments of a degree of polymerization ≥13 produced by SsGDE debranching could also be utilized by ß-CGTase to convert into CDs. Overall, these findings proposed a new approach of combining SsGDE with ß-CGTase to enhance the CD yield.

A new micro-agar dilution method to determine the minimum inhibitory concentration of essential oils against microorganisms.

Essential oils (EOs) from plants have attracted wide attention due to their unique flavors and antimicrobial, insecticidal, antioxidant, and anti-inflammatory properties. Antimicrobial activity, the main reason for their widespread use in the food industry, can be determined in vitro by the minimum inhibitory concentration (MIC), which is a key step to evaluate the antimicrobial potential of EOs. However, EOs are lipophilic and insoluble, resulting in the difficulty of accurately measuring their MIC values. In this study, in addition to analyzing the problems in the MIC determination of EOs using the common micro-broth dilution method or the agar method, a new solution called micro-agar dilution method was proposed. As the miniaturization of agar dilution method, this novel method could reduce the dosage of EOs by 16.3 times and medium/PBS by 3.3 times, respectively, and showed better reliability and accuracy than the typical methods. Additionally, the limit of solvents should be evaluated before use if used. Notably, this research could also provide a guide for the MIC determination of other insoluble antibacterial substances.

A review of controlled release from cyclodextrins: release methods, release systems and application.

The controlled release of guest molecules from cyclodextrin (CD) inclusion complexes is very important for specific industrial applications in foods, medicine, cosmetics, textiles, agriculture, environmental protection, and chemical materials. The term "controlled release" encompasses several related methods, including those referred to as immediate release, sustained release and targeted release. Many different CD-based controlled release systems are currently used in practical applications. CD inclusion complexes, CD coupling, supramolecular hydrogels, and supramolecular micelles are among the most common. This review systematically introduces the principles and applications of CD-based controlled release systems, providing a theoretical basis for improving the bioavailability of effective substances and broadening their range of application.

A two-stage modification method using 1,4-α-glucan branching enzyme lowers the in vitro digestibility of corn starch.

Samples of granular corn starch were treated with 1,4-α-glucan branching enzyme (GBE) for 20 h using three different methods. These GBE modification methods all increased glycosidic linkage ratio, cyclic glucan content, and proportion of short chains while reducing weight mean molecular weight. The in vitro digestion rates of the modified starches were suppressed. Among these methods, a novel two-stage modification method comprising a 10-h GBE treatment, gelatinization, and a second 10-h GBE treatment, produced samples with the lowest in vitro digestibility. The rapidly digestible starch content was 34.2% lower than that of the control and 18.0% lower than that of the product of one-stage modification with the same duration. Fine structure characterization showed that more cluster structures were proved during the two-stage modification. This two-stage method suppressed the digestibility of corn starch and increased the substrate concentration, showing great potential for the industrial processing of slowly-digestible starchy foods.

Variants at position 603 of the CGTase from Bacillus circulans STB01 for reducing product inhibition.

Inhibition of cyclodextrin glycosyltransferases (CGTases) by their product cyclodextrins limits the efficiency of cyclodextrin production. In an effort to produce variants with good activity but reduced product inhibition, six mutants were constructed at position 603 of the CGTase from Bacillus circulans STB01, which exhibits mixed-type product inhibition. In a kinetic analysis, N603I showed reduced noncompetitive inhibition while N603K, N603H and N603R showed increased noncompetitive inhibition. Unexpectedly, N603E and N603D exhibited reductions in both competitive and noncompetitive product inhibition. Noncompetitive product inhibition is closely related to the interaction between the cyclodextrin and the enzyme in maltose binding site 2 (MBS2). Structural models led to the suggestion that there is increased interaction between maltose binding sites 1 and 2 in mutants N603E and N603D, which may have led to the unexpected results. N603D exhibited a 23.9% greater cyclodextrin yield per gram of enzyme than the wild-type, suggesting it has potential for industrial use. Further reductions in product inhibition may be gained through studies of maltose binding site interactions.

Clinical Effect of Intravenous Vitamin C on Viral Myocarditis in Children: A Systematic Review and Meta-Analysis.

OBJECTIVE: To comprehensively compare the effects of conventional therapy combined with intravenous vitamin C and conventional therapy on viral myocarditis in children through a meta-analysis. METHODS: Relevant articles including clinical trials of normal treatment combined with intravenous vitamin C and conventional therapy for viral myocarditis in children that were published between January 2000 and February 2018 were selected from PubMed, Cochrane Library, China National Knowledge Infrastructure, China Science and Technology Journal Database, and WANFANG database. The quality of the included studies was assessed using the Cochrane systematic review method (version 5.1.0); data quality was evaluated by two independent researchers. The total effective rate; LDH, CK, and CK-MB levels; and other indicators were analyzed using Rev Man 5.3 software. RESULTS: Eight studies were eligible for this meta-analysis, which included a total of 426 patients in the treatment group and 363 patients in the control group. The meta-analysis results of six studies showed that the total effective rate of intravenous vitamin C combined with conventional therapy was higher than that of conventional therapy alone [Z = 5.46, 95% confidence interval (CI): 1.21 (1.13 to 1.30), P < 0.00001]; that of five studies showed that LDH levels were lower in children receiving intravenous vitamin C combined with conventional therapy than in those receiving conventional therapy alone [Z = 3.70, 95% CI: -1.88 (-2.88 to -0.88), P = 0.0002]; that of three studies showed that CK levels were lower in children receiving intravenous vitamin C combined with conventional therapy than in those receiving conventional therapy alone [Z = 4.21, 95% CI: -0.55 (-0.81 to -0.30), P < 0.0001]; that of four studies showed that CK-MB levels were lower in children receiving intravenous vitamin C combined with conventional therapy than in those receiving conventional therapy alone [Z = 13.64, 95% CI: -1.44 (-1.65 to -1.24), P < 0.00001]; that of two studies showed that CD3 levels were higher in children receiving intravenous vitamin C combined with conventional therapy than in those receiving conventional therapy alone [Z = 2.45, 95% CI: 0.41 (0.08-0.73), P = 0.01]; that of two studies showed no significant difference in changes in CD4 levels between children receiving intravenous vitamin C combined with conventional therapy and those receiving conventional therapy alone [Z = 0.28, 95% CI: -0.21 (-1.69 to 1.28), P = 0.78]; and that of two studies showed no significant difference in changes in CD4/CD8 between children receiving intravenous vitamin C combined with conventional therapy and those receiving conventional therapy alone [Z = 0.07, 95% CI: -0.03 (-0.73 to 0.67), P = 0.94]. CONCLUSION: The meta-analysis results showed that intravenous vitamin C combined with conventional therapy is better than the simple, conventional therapy for the treatment of viral myocarditis in children in terms of the total effective rate and LDH, CK, and CK-MB levels.

Leu600 mutations decrease product inhibition of the ß-cyclodextrin glycosyltransferase from Bacillus circulans STB01.

The limits that cyclodextrin products impose on their industrial production from starch by cyclodextrin glycosyltransferases (CGTases) are a severe problem. In this paper, mutants at residue Leu600 of the ß-CGTase from Bacillus circulans STB01 were constructed in an effort to decrease the product inhibition exhibited by ß-cyclodextrin. A kinetic analysis of the inhibition of the wild-type and mutant ß-CGTases by ß-cyclodextrin revealed that the mutations do not alter the inhibition mode, which is mixed-type. However, the values of the inhibition constants (Ki and Ki') of the mutants L600I, L600E and L600R are higher than those of the wild-type enzyme, weakening the product inhibition. The mutant L600Y only exhibited a decrease in noncompetitive inhibition, with the value of Ki' increasing by 40%. Comparison of the Km' values and the 3D model structures of the wild-type and mutant CGTases suggests that this decrease in product inhibition is related to a decrease in binding affinity between the product cyclodextrin and the enzyme.