Yaoqi Tian

Influence of low ultrasound intensity on the degradation of dextran catalyzed by dextranase

In our current research work, the effect of ultrasound irradiation on the enzymatic activity and enzymatic hydrolysis kinetic parameters of dextran catalysis by dextranase were investigated. Furthermore, the effects of ultrasound irradiation on the structure of dextranase were investigated with the aid of fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The maximum activity of dextranase was observed when the sample was treated with ultrasound at 25 kHz, 40 W for 15 min, under which the enzyme activity increased by 13.43% compared the routine thermal incubation at 50 °C. Experimental Kinetics results, demonstrated that, both the V(max) and K(M) values of dextranase increased with ultrasound-treated compared with the incubation at 50 °C. Likewise, both the catalytic and specificity constants were higher under the effects of an ultrasonic field, indicating that, the substrate is converted into the product at an increased rate when compared with the incubation at 50 °C. On the other hand, fluorescence and CD spectra reflected that the ultrasound irradiation had increased the number of tryptophan on dextranase surface with increased α-helix by 15.74% and reduced random coil by 5.41% upon ultrasound-treated dextranase protein compared to the control, which were helpful for the improvement of its activity.

Surface chemical compositions and dispersity of starch nanocrystals formed by sulfuric and hydrochloric acid hydrolysis.

Surface chemical compositions of starch nanocrystals (SNC) prepared using sulfuric acid (H2SO4) and hydrochloric acid (HCl) hydrolysis were analyzed by X-ray photoelectron spectroscopy (XPS) and FT-IR. The results showed that carboxyl groups and sulfate esters were presented in SNC after hydrolysis with H2SO4, while no sulfate esters were detected in SNC during HCl-hydrolysis. TEM results showed that, compared to H2SO4-hydrolyzed sample, a wider size distribution of SNC prepared by HCl-hydrolysis were observed. Zeta-potentials were −23.1 and −5.02 mV for H2SO4- and HCl-hydrolyzed SNC suspensions at pH 6.5, respectively. Nevertheless, the zeta-potential values decreased to −32.3 and −10.2 mV as the dispersion pH was adjusted to 10.6. After placed 48 h at pH 10.6, zeta-potential increased to −24.1 mV for H2SO4-hydrolyzed SNC, while no change was detected for HCl-hydrolyzed one. The higher zeta-potential and relative small particle distribution of SNC caused more stable suspensions compared to HCl-hydrolyzed sample.

Polyphenols from blueberries modulate inflammation cytokines in LPS-induced RAW264.7 macrophages

Polyphenols including 3-glucoside/arabinoside/galactoside-based polymers of delphinidins, petunidins, peonidins, malvidins and cyanidins are one type of biological macromolecules, which are extraordinarily rich in blueberries. Anti-inflammatory activity of blueberry polyphenols (BPPs) was investigated by using lipopolysaccharide (LPS) induced RAW264.7 macrophages. The results showed that BPPs suppressed the gene expression of IL-1β (interleukin-1β), IL-6 and IL-12p35. The inhibition effect on IL-1β and IL-6 mRNA was most obvious at the concentration of 10-200μg/mL BPPs. But the inhibition effect on IL-12p35 mRNA was increased with the increasing concentration of BPPs. When fixed at 100μg/mL BPPs, the most significant inhibition on IL-1β, IL-6 and IL-12p35 mRNA expression was detected at 12-48h. In conclusion, BPPs exhibit anti-inflammation activity by mediating and modulating the balances in pro-inflammatory cytokines of IL-1β, IL-6, and IL-12.

Effect of high hydrostatic pressure (HHP) on slowly digestible properties of rice starches

The slowly digestible properties of high hydrostatic pressure (HHP)-gelatinized non-waxy and waxy rice starches during the retrogradation were evaluated in this study. The results show that slowly digestible starch (SDS) was observed at a higher percentage in HHP-gelatinized, non-waxy and waxy rice starches than in heat-gelatinized starches, after retrogradation for 7 days. The HHP treatment significantly reduced the enthalpy change of starch retrogradation and retarded the freezable water transformation into unfreezable water during retrogradation. This indicated that the SDS percentage was not positively correlated to the retrogradation degree of starch. Furthermore, X-ray diffraction (XRD) data revealed that the HHP treatment decreased the perfect crystallites of the 7 day-retrograded. Non-waxy and waxy starches from 19.5% to 12.1% and 15.7% to 11.4%, while increased imperfect crystallites from 26.4% to 30.7% and 28.6% to 31.3%, respectively. These findings suggest that the higher SDS percentage can be attributed to the formation of less perfect crystallites and more imperfect crystallites during the HHP and retrogradation treatments.

Preparation of the β-cyclodextrin-vitamin C (β-CD-Vc) inclusion complex under high hydrostatic pressure (HHP)

In this study, a novel high hydrostatic pressure (HHP) technique was used to prepare the β-cyclodextrin-vitamin C (β-CD-Vc) inclusion complex. The inclusion ratio was positively correlated with the pressure under 300 MPa and remained at above 50.0% when the pressure was more than 300 MPa. Fourier-transform infrared spectroscopy (FI-IR) and UV-visible spectroscopy (UV-vis) analysis showed that characteristic absorption bands and the absorption peak of Vc disappeared in the spectra of the β-CD-Vc inclusion complex. Furthermore, differential scanning calorimetry (DSC) data revealed that only one endothermic peak appeared at about 138 °C in the DSC curve of the β-CD-Vc inclusion complex. These results indicate that the HHP treatment effectively induces the formation of β-CD-Vc inclusion complex.

Effect of temperature-cycled retrogradation on slow digestibility of waxy rice starch

The temperature-cycled retrogradation conditions were optimized for producing slowly digestible starch (SDS) products in this study. The present data showed that the following conditions (temperature cycle, 4/25°C; temperature-cycled time, 14 d; temperature-cycled time interval, 24 h; and ratio of starch to water, 1:2) were available for increasing the SDS yield of the products. The maximum yield reached 54.5%, while the SDS products were prepared under the optimum conditions. The results also indicated that temperature-cycled retrogradation significantly increased the slow digestibility of the SDS products. This was probably attributed to many solid blocks remaining after the hydrolysis of the SDS products by the enzymes for 60 min and 120 min. The solid blocks may comprise of more imperfect crystallites and part of amorphous non-digestible starch. These results suggest that the optimum conditions obtained are suited for preparing SDS products in food and pharmaceutical industries.

Biochemical characterization of an intracellular 6G-fructofuranosidase from Xanthophyllomyces dendrorhous and its use in production of neo-fructooligosaccharides (neo-FOSs)

An intracellular 6G-fructofuranosidase (endo-type enzyme) extracted from Xanthophyllomyces dendrorhous 269 efficiently hydrolyzes fructosyl-β-(2→1)-linked sucrose to produce neo-kestose as a main transglycosylation product. The enzyme with a molecular weight of 33 kDa was purified by DEAE-52 cellulose chromatography. Thirty-fivefold purification and a 13.4% enzyme activity recovery were achieved. Optimum enzyme activity occurred at pH 6.4 and 45 °C and the enzyme was stable at pH 4-7 and at 45 °C. Using sucrose as a substrate, the Km and Vmax values were, respectively, 511 mmol/l and 233 μmol/(min mg) for transfer activity and 62 mmol/l and 164 μmol/(min mg) for hydrolytic activity. Under optimum conditions, a maximum concentration (73.9 g/l) of neo-fructooligosaccharides catalyzed by the endo-enzyme was obtained. These findings suggest that the purified endo-enzyme exhibits a high transfructosylation activity and it has potential for the industrial production of neo-FOSs.

Identification and releasing characteristics of high-amylose corn starch-cinnamaldehyde inclusion complex prepared using ultrasound treatment.

In this study, the high-amylose corn starch-cinnamaldehyde inclusion complex was prepared by an ultrasound treatment and its releasing characteristic was investigated. The results showed that the ultrasound treatment (35°C, 10min and 250W) generated a higher encapsulation rate of 40.2% than the conventional treatment (encapsulation rate, 5.7%). Data obtained from Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA) indicated that cinnamaldehyde was successfully encapsulated by high-amylose corn starch and the encapsulation significantly increased the dissociation temperature of cinnamaldehyde by around 70°C. Compared to the physical mixture of high-amylose corn starch and cinnamaldehyde, the formed inclusion complex had good retention ability and reduced the releasing rate of cinnamaldehyde from 57.5% to 28.4% in the first week. These results suggest that cinnamaldehyde could be encapsulated by high-amylose corn starch with an ultrasound treatment for presenting the releasing behavior in food preservation.

Effect of pullulan on the water distribution, microstructure and textural properties of rice starch gels during cold storage

The effects of pullulan on the water distribution, microstructure and textural properties of rice starch gels during cold storage were investigated by low field-nuclear magnetic resonance (LF-NMR), scanning electron microscope (SEM), and texture profile analysis (TPA). The addition of pullulan reduced the transversal relaxation time of rice starch gels during cold storage. The microstructure of rice starch gel with 0.5% pullulan was denser and more uniform compared with that of rice starch without pullulan in each period of storage time. With regard to textural properties, 0.01% pullulan addition did not significantly change the texture of rice starch gels, while 0.5% pullulan addition appeared to reduce the hardness and retain the springiness of rice starch gels (P⩽0.05). The restriction effects of pullulan on water mobility and starch retrogradation were hypothesized to be mainly responsible for the water retention, gel structure maintenance, and modification of the textural attributes of rice starch gels.

Stabilization of starch-based microgel-lysozyme complexes using a layer-by-layer assembly technique.

The layer-by-layer assembly of polyelectrolyte multilayers of chitosan (CS) and carboxymethyl starch (CMS) on soft and porous pH- and ionic strength-response microgels was determined by confocal laser scanning microscopy (CLSM) and zeta potential measurements. In vitro release of lysozyme from the stabilized microgels under simulated gastric and intestinal fluids was also investigated. The distribution of CS in the microgels was identified by CLSM, and the optimal molecular weight of CS was 100kDa, which could only be absorbed on the microgel surface. The CS was used as the first layer, while the CMS was used as the second layer, and the zeta potential revealed that the optimal weight ratios of CS and CMS to microgels in the complexes were 0.1 and 0.06, respectively. The in vitro release experiments suggested that the stabilized double-layer microgel complexes could potentially be applied as a carrier system to prevent early release in the stomach to target intestinal delivery.