The present study was performed to investigate binary and tertiary nanocomposites between short-chain glucan (SCG) and proanthocyanidins (PAC) for the oral delivery of insulin. There was a large decrease in fluorescence intensity of insulin in the presence of SCG or the combination of SCG with PAC. Fourier transform infrared spectroscopy revealed that the binary and tertiary nanocomposites were synthesized due to the hydrogen bonding and hydrophobic interactions. The insulin entrapped in the nanocomposites was in an amorphous state confirmed by X-ray diffraction. The cell culture demonstrated that both the nanocomposites showed no detectable cytotoxicity with relative cell viability all above 85%. The pharmacological bioavailability after oral administration of insulin–SCG–PAC at a dose of 100 IU/kg was found to be 6.98 ± 1.20% in diabetic rats without any sharp fluctuations in 8 h.Keywords: bioavailability; hypoglycemic effect; in vivo; nanocomposites;

Lauryl sodium sulfate (LSS) combined with alkylphenol ethoxylates (APEO) were used to enhance the performance of a high starch content wood adhesive (HSWA). The optimal shear strength, mobility and viscosity stability of the wood adhesive after repeated freeze–thaw cycling were gained when LSS to APEO ratio was 7 to1, which could efficiently solve storage problems caused by a high starch content. Through blue value and differential scanning calorimetry (DSC) analysis, it was proved that the structure of the complexes formed between amylose and the compound emulsifiers with LSS/APEO mixing ration of 7:1 was the most stable. Scanning electron microscopy (SEM) images and particle size analysis showed that compound emulsifiers could significantly suppress the aggregation of emulsion particles. The mechanism could be, on the one hand, attributed to stable complexes formed by compound emulsifiers and amylose which could restrain starch retrogradation, and on the other to the synergetic effect of electrostatic charge forces and space steric hindrances caused by the LSS/APEO mixture adsorbed on the surface of latex particles. In conclusion, the addition of an LSS/APEO(mixing ratio 7:1) mixture could significantly prevent the aggregation of latex particles and retrogradation of starch molecules, indicating that these compound emulsifiers could be applied in the preparation of a high starch content wood adhesive.

•Confocal Raman microscopy was used to detect the reaction homogeneity of vinyl acetate grafted on maize starch granules.•The quality of high solid content starch based wood adhesive was related to the reaction homogeneity.•The analysis of grafted single starch granules by CRM is a useful method to acquire information about reaction homogeneity.Confocal Raman microscopy (CRM) was used to detect the reaction homogeneity of vinyl acetate grafted on starch granules and help to assess the quality of high solid content starch-based wood adhesive (HSSWA). Primarily, four experimental starch samples were investigated, and by analysis of band area ratio (carbonyl/carbohydrate) of each granule, information about reaction homogeneity was collected. The results showed that reaction extent and homogeneity were inconsistent for samples with different G values, and the distribution of ester groups on blend samples was much less uniform than grafted starch samples with the same G value, confirming that CRM was useful for determining the homogeneity of chemical modification. Afterwards, the technique was applied to research HSSWA prepared by two-stage seeded polymerization and traditional process. The distribution of ester groups was more uniform among starch granules prepared by former method, resulted in adhesive with much better performance, indicating that uniformity of polymerization was an important factor related to properties of starch-based wood adhesive.

•Impact of amylose content on starch physicochemical properties was studied.•Waxy and high-amylose starches had different chain length distribution from the normal starch.•The transition from the type-A crystal form of low-amylose starches to the type-B crystal form of high-amylose staches was revealed.•High amylose increased the shear stress resistance of starch gel after gelatinization.•Novel starches for various applications were developed in sweet potato.The intrinsic relationship between amylose content and starch physicochemical properties was studied using six representative starch samples (amylose content 0–65%) produced from transgenic sweet potato (cultivar Xushu22). The transgenic lines (waxy and high-amylose) and wild-type (WT) sweet potatoes were analyzed for amylose content, particle size and chain length distribution, X-ray diffraction analysis, thermal characteristics, pasting and rheological property. Compared to the WT starch, the waxy and high-amylose starches showed larger average granule sizes and had fewer short chains and more medium and long chains. X-ray diffractogram analysis revealed that high-amylose starches show a type-B crystal form with a markedly decreased degree of crystallinity in contrast to the type-A crystal form of the WT and waxy starches. In the high-amylose sweet potato starches, the rise of setback value and the reduction of breakdown value led to the high shear resistance as indicated by the higher G′, G″, and tan δ from the oscillation test. ΔH was not found to be decreased with the reduction of crystallinity. The shear stress resistance of starch gel after gelatinization was also enhanced as amylose content increased. Principal component analysis also confirmed that the amylose content greatly influenced the starch structure and properties, e.g., storage modulus, setback value, and average chain length. Thus, our study not only shed light on how amylose content affects starch properties but also identified novel starches that are available for various applications.

•Montmorillonite enhanced the shear strength of adhesive.•Montmorillonite enhanced shear-thinning and solid-like behaviors.•Montmorillonite improved thermal stability of the adhesive.•Montmorillonite could be dispersed in the adhesive.Effects of montmorillonite (MMT) addition on the performance of corn starch-based wood adhesive were investigated. It was found that MMT addition could enhance the shear strength of the starch-based wood adhesive. The shear strength of the adhesive with 5% (w/w, dry starch basis) MMT reached 10.6 MPa in the dry state, which was almost twice that of the same adhesive without MMT. Addition of 5% MMT also produced an approximately 1.2-fold increase in the shear strength in the wet state. Although this addition caused an increase in the viscosity, the resulting adhesive retained both good mobility and viscosity stability during storage. MMT also enhanced the shear-thinning and solid-like behaviors of the adhesive, compared with the adhesive without MMT. Finally, MMT addition improved the thermal stability of the adhesive. In conclusion, addition of MMT to starch-based wood adhesives can improve their overall performance, enhancing their value as alternatives for traditional petrochemical-based wood adhesives.

Debranched starches (DBSs) with different degrees of debranching (low, L-DBS; moderate, M-DBS; high, H-DBS) were prepared and investigated. After pullulanase modification, the starch granules became more porous and many small particles containing short glucan chains were generated. DBSs adopt a single-helical V-type crystalline structure with low crystallinity. L-DBS samples contained fewer (20.70%) and longer (degree of polymerization, DP: 21.92) linear short glucan chains than their counterparts (M-DBS: 40.92%, 20.05 DP; H-DBS: 55.52%, 18.52 DP). Pullulanase enzymatic hydrolyzate for DBS samples with higher degrees of debranching inclined towards retrogradation at 20 °C. DBSs with higher degrees of debranching could form a hydrogel with higher G′ and G′′ values, indicating these samples formed a stronger gel network. L-DBS could hold more water and its digestibility was higher. The in vitro test showed that DBS is a good candidate to control drug release for over 12 h. Furthermore, the drug release profiles from both DBS-based and HPMC-based tablets showed an anomalous transport mechanism. The drug release from these four matrices was controlled by a combination of drug diffusion and matrix erosion. The drug release properties from DBS-based tablets were considerably influenced by the degree of debranching. The in vitro drug release profile of M-DBS was similar to that of HPMC (f2 = 60.75), while L-DBS and H-DBS differed from HPMC (f2 < 50). In summary, DBS is a good hydrogel candidate, and it can be used as an excipient in oral tablets to control drug release.

•PEG 400 enhances the activity of β-cyclodextrin glycosyltransferase by 20%.•PEG 1000 prolongs the half-life of this enzyme at 60 °C by 6.5-fold.•Fluorescence spectroscopy shows that PEGs protect tertiary structure.•Circular dichroism shows that PEGs protect secondary structure.We investigated the ability of six polyethylene glycols (PEGs), with molecular weights ranging from 400 to 20,000 Da, to enhance the thermostability of β-cyclodextrin glycosyltransferase (β-CGTase) from Bacillus circulans. We found that PEGs with different molecular weights could activate and stabilize this β-CGTase, but to different degrees. The most significant increase (about 20%) in β-cyclodextrin-forming activity was achieved by adding 10–15% PEG 400. PEGs with low molecular weights also significantly enhanced the thermostability of β-CGTase; 15% PEG 1000 prolonged its half-life at 60 °C by 6.5-fold, compared to a control. Fluorescence spectroscopy and circular dichroism analysis indicated that PEGs helped protect the tertiary and secondary structure of β-CGTase, respectively. This study provides an effective approach for improving the thermostability of CGTases and related enzymes.

•The effects of residue 31 on product specificity of CGTase were investigated.•The mutation A31R could enhance β-cyclodextrin specificity of the CGTase.•The mutant A31R was very suitable for the industrial production of β-cyclodextrin.•CaI might play an important role in cyclodextrin product specificity of CGTase.The effects of amino acid residue at position 31 in the neighborhood of calcium binding site I (CaI) on product specificity of cyclodextrin glycosyltransferase (EC 2.4.1.19, CGTase) were investigated by replacing Ala31 in the CGTase from Bacillus circulans STB01 with arginine, proline, threonine, serine and glycine. The results showed that the mutations A31R, A31P, and A31T resulted in the increases in β-cyclodextrin-forming activity and β-cyclodextrin production, indicating that these mutations enhanced β-cyclodextrin specificity of the CGTase. Especially the mutant A31R displayed approximately 26% increase in β-cyclodextrin production with a concomitant 41% decrease in α-cyclodextrin production when compared to the wild-type CGTase. Thus, it was much more suitable for the industrial production of β-cyclodextrin than the wild-type enzyme. The enhanced β-cyclodextrin specificity of the mutants might be a result of stabilizing CaI, which also suggested that CaI might play an important role in cyclodextrin product specificity of CGTase.

•SDS enhanced the mobility of starch-based wood adhesive.•SDS resulted in higher storage stability of starch-based wood adhesive.•SDS improved the performance of starch-based wood adhesive.•Amylose–SDS complexes could be formed in starch.Sodium dodecyl sulfate (SDS) was used to improve the performance of starch-based wood adhesive. The effects of SDS on shear strength, viscosity and storage stability were investigated. It was shown that, although the addition of 1.5–2% (dry starch basis) SDS resulted in a slight decrease in shear strength, the mobility and storage stability of adhesive were significantly enhanced. Possible mechanisms regarding specific action of SDS were discussed. It was proved, using blue value or differential scanning calorimetry (DSC) analysis, that the amylose–SDS complexes were formed in the adhesive. The complex formation or simple adsorption of SDS with starch molecules might hinder the aggregation of latex particles, as shown by scanning electron microscopy images, and inhibit starch retrogradation, as observed by DSC analysis. As a result, in the presence of SDS, the adhesive had higher mobility and storage stability, indicating that SDS could be used to prepare starch-based wood adhesives with high performance.

A major disadvantage of cyclodextrin production is the limited thermostability of cyclodextrin glycosyltransferase. The ability of combinations of nanosilica sol with polyethylene glycol (PEG) 1000 to enhance the thermostability of the β-cyclodextrin glycosyltransferase from Bacillus circulans was investigated. It was found that 10% PEG 1000 combined with 0.05% nanosilica sol could activate the β-cyclodextrin glycosyltransferase by 17.2%. Furthermore, 0.05% nanosilica sol leads to further increase in PEG 1000-enhanced thermostability of β-cyclodextrin glycosyltransferase. With the simultaneous addition of 10% PEG 1000 and 0.05% nanosilica into the enzyme solution, which was allowed to incubate for 60 min at 60 °C, 61.3% of β-cyclodextrin-forming activity could be retained, which was much higher than that with only 10% PEG 1000 added. Atomic force microscopy, fluorescence spectroscopy, and circular dichroism analysis indicated that silica nanoparticles helped PEG 1000 further protect the tertiary and secondary structures of β-cyclodextrin glycosyltransferase. This study provides an effective approach for improving the thermostability of cyclodextrin glycosyltransferase and related enzymes.

In the study, we investigated the contribution of Ca2+ to the thermostability of α-cyclodextrin glycosyltransferase (α-CGTase) from Paenibacillus macerans, which has two calcium-binding sites (CaI and CaII), and β-CGTase from Bacillus circulans, which contains an additional calcium-binding site (CaIII), consisting of Ala315 and Asp577. It was found that the contribution of Ca2+ to the thermostability of two CGTases displayed a marked difference. Ca2+ affected β-CGTase thermostability significantly. After Ca2+ was added to β-CGTase solution to a final concentration of 5 mM followed by incubation for 120 min at 60 °C, residual activity of β-CGTase was 88.3%, which was much higher than that without Ca2+. However, Ca2+ had a small contribution to α-CGTase thermostability. Furthermore, A315D and D577K mutations at CaIII could significantly change the contribution of Ca2+ to β-CGTase thermostability. These results suggested that the contribution of Ca2+ to CGTase thermostability was closely related to CaIII.

The amino acid residue Asp 577 is located in calcium-binding site III (CaIII) of the cyclodextrin glycosyltransferase (EC 2.4.1.19, CGTase) from Bacillus circulans STB01. In the present study, the effects of replacing Asp577 with glycine, alanine, valine, leucine, and isoleucine on the catalytic efficiency of this CGTase were investigated. Two of these replacements, D577G and D577A, increased the β-cyclization activity of CGTase. Kinetic studies showed that the Km values of D577G and D577A were 36.1% and 18.0% lower and the kcat/Km values were 43.9% and 23.0% higher than those of the wild-type enzyme, respectively. These mutations increased both the affinity of CGTase for maltodextrin and the catalytic efficiency of the cyclization reaction. Furthermore, although D577G and D577A only slightly enhanced β-cyclodextrin production, compared with the wild-type enzyme, their higher β-cyclization activities resulted in a significant reduction in the amount of mutant protein required during the cyclodextrin production process. Thus, the two mutants are more suitable for the industrial production of β-cyclodextrin than the wild-type enzyme. The enhancement of catalytic efficiency may be due to the smaller size of the glycine and alanine side chains, which may weaken the impact of this residue on CaIII.