Benxi Wei

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.

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.

Characterization of different substituted carboxymethyl starch microgels and their interactions with lysozyme.

A carboxymethyl starch (CMS) microgel system was prepared for the control of uptaking and releasing proteins (lysozyme). The physicochemical properties of microgels in various degrees of substitution (DS) were determined by thermal gravimetric analysis (TGA), swelling degree, and rheological analysis. The microgel particle size mostly ranged from 25 µm to 45 µm. The result obtained from the TGA studies indicated that carboxymethylation decreased the thermal stability of starch, but crosslinking increased the thermal stability of CMS. The CMS microgels showed typical pH sensitivity, and the swelling degree of microgel increased with the increasing of DS and pH, because of the large amounts of carboxyl group ionization. The samples (2.25%) could behave as viscoelastic solids since the storage modulus was larger than the loss modulus over the entire frequency range. The protein uptake increased with increasing pH and DS at low salt concentration. The optimal pH shifted to lower pH with increasing ionic strength. The saturated protein uptake decreased with increasing ionic strength at each pH. The protein was easily released from the microgel with high pH and high salt concentration.

Effect of defatting on acid hydrolysis rate of maize starch with different amylose contents.

The effect of defatting on the physiochemical properties and the acid hydrolysis rate of maize starch with different amylose contents was evaluated in this study. The increase in the number of pores and the stripping of starch surface layers were observed after defatting by scanning electron microscopy. X-ray diffraction spectrum showed that the peaks attributing to the amylose-lipid complex disappeared. The relative crystallinity increased by 19% for high-amylose maize starch (HMS) on defatting, while the other tested starches virtually unchanged. Differential scanning calorimetry study indicated an increase in the thermal stability for the defatted starches. Compared with native waxy maize starch, the acid hydrolysis rate of the defatted one increased by 6% after 10 days. For normal maize starch (NMS) and HMS, the higher rate of hydrolysis was observed during the first 5 days. Thereafter, the hydrolysis rate was lower than that of their native counterpart. The increase in susceptibility to acid hydrolysis (in the first 5 days) was mainly attributed to the defective and porous structures formed during defatting process, while the decrease of hydrolysis rate for NMS and HMS samples (after the first 5 days) probably resulted from the increase in the relative crystallinity.

Synthesis, characterization and hydrophobicity of silylated starch nanocrystal.

Starch nanocrystal (SNC) was silylated by hexadecyltrimethoxysilane (HDS) aiming to improve its hydrophobicity. HDS was firstly hydrolyzed in ethanol/water and then adsorbed onto SNC through hydrogen bonds, finally the long chain hydrocarbon was covalently linked to the surface of SNC through SiOC bonds which formed via the condensation reaction between hydroxyl and silanol groups. Due to the multilayer coverage of the hydrolyzed HDS, the long chain hydrocarbon crystalized on the surface of SNC and superimposed over the original A-type starch diffraction pattern. Both the hydrophobicity and hydrophobic stability were increased with the increase of the applied HDS. The contact angle of modified SNC increased from 43° to 119° as the applied HDS increased from 0% to 0.3% (v/v). The modification significantly improved its dispersibility in non-polar solvents and a homogenous suspension could be formed in acetone and n-hexane.

Thermal degradation behavior of hypochlorite-oxidized starch nanocrystals under different oxidized levels

The thermal degradation behavior of hypochlorite-oxidized starch nanocrystals (OSNCs) was evaluated in this study. Carbonyl and carboxyl groups in OSNCs increased from 0.006 and 0.091mmol/g to 0.033 and 0.129mmol/g, respectively, as the active chlorine concentration increased from 1% to 4% (w/w). Compared with starch nanocrystals (SNCs), the initial degradation temperature of OSNCs with 4% oxidization decreased from 273°C to 253°C. Two degradation processes were detected using differential thermal analysis. The activation energy of the low-temperature process increased with increasing oxidization level because of removal of sulfate esters and reduction of the decomposition products of H2O during oxidation. With increasing temperature, the H2O generating from decarboxylation and decomposition of the carboxyl groups may catalyze SNCs depolymerization, leading to decrease in the activation energy of the high-temperature process. OSNCs (4% oxidized level) can be used in dry process below 253°C to avoid degradation.

Preparation and characterization of carboxymethyl starch microgel with different crosslinking densities

Microgels synthesized with different crosslinking densities were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry analysis (TGA), swelling, and rheological analyses. The lysozyme uptake capacity of these microgels was evaluated through the effects of lysozyme concentration, pH, and ionic strength. The microgel particle size mostly ranged within 25μm to 45μm. FT-IR analysis results suggested that sodium trimetaphosphate reacted with the hydroxyl groups of carboxymethyl starch (CMS), thereby forming ester linkages. TGA data indicated that crosslinking increased the thermal stability of CMS. Swelling degree increased with increasing pH before pH 5, and then remained almost constant. However, swelling degree decreased with increasing ionic strength and crosslinking density. The microgels behaved as viscoelastic solids because the storage modulus was higher than the loss modulus over the entire frequency range of dispersions with polymer concentrations of 3% (W/W) at 25°C. The data for the uptake of lysozyme by microgels demonstrated that the protein uptake increased with increasing pH and lysozyme concentration, as well as with decreasing ionic strength and crosslinking density. The lysozyme-microgels complex was identified by CLSM, and the distribution of lysozyme in microgels with low crosslinking density was rather homogeneous.

Porous starch extracted from Chinese rice wine vinasse: characterization and adsorption properties.

Chinese rice wine vinasse (the fermentation residue after removal of the crude wine or beer) contains 20-30% residual native starch. These starches are partly hydrolyzed by amylase and glucoamylase during rice wine fermentation, indicating that it is a potential source of porous starch, which is a value-added material. In the present study, morphological, short-range order, crystalline, and thermal studies were determined to characterize the structural and chemical properties of vinasse starch. The results showed that vinasse starch granule had a rough and porous shape and was much more ordered than native starch. Vinasse starch also could tolerate a higher temperature than native starch. The water and oil adsorptive capacities of vinasse starch were 1.89 and 4.14 times higher than that of native rice starch. These results suggest that vinasse is an effective and economical source of porous starch for using as adsorbent.

Synthesis and characterization of dextrin monosuccinate.

Reaction conditions, including reaction solvents, reaction time, reaction temperature, and molar ratio of succinic anhydride (SA) to anhydroglucose units (AGU) in dextrin, were investigated for preparing dextrin monosuccinate with high degree of substitution (DS). The results showed the optimum conditions as follows: Solvent, dimethyl sulfoxide; reaction temperature, 50°C; reaction time, 16 h; and molar ratio of SA to AGU in dextrin, 6:1. Under these conditions, the maximum DS reached 2.64. The chemical structure of dextrin monosuccinate was identified using FT-IR and (13)C NMR. The FT-IR data indicated the absorption bands of esters and carbonyl acids at 1726 and 1,574 cm(-1). Signals at 173.13, 171.81, 28.79, and 28.61 ppm in (13)C NMR spectrum were ascribed to carbons in ester, carbonyl acid, and methylene. These data suggest that the prepared dextrin succinate was monoester with functional carbonyl acid groups and could be used in polymer therapy as drug carriers.

Impact of α-amylase combined with hydrochloric acid hydrolysis on structure and digestion of waxy rice starch

The structure and in vitro digestibility of native waxy rice starch by the combined hydrolysis of α-amylase and hydrochloric acid were investigated in this study. The combined hydrolysis technique generated higher hydrolysis rate and extent than the enzymatic hydrolysis. The granular appearance and chromatograph profile demonstrated that α-amylase and hydrochloric acid exhibited different patterns of hydrolysis. The rise in the ratio of absorbance 1047/1022cm(-1), the melting temperature range (Tc-To), and the melting enthalpy (ΔH) were observed during the combined hydrolysis. These results suggest that α-amylase simultaneously cleaves the amorphous and crystalline regions, whereas the amorphous regions of starch granules are preferentially hydrolyzed during the acid hydrolysis. Furthermore, the combined hydrolysis increased rapidly digestible starch (RDS) while decreased slowly digestible starch (SDS) and resistant starch (RS), indicating that the hydrolysis mode affected the digestion property of native waxy rice starch.