Bao Zhang

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.

Synthesis of pH- and ionic strength-responsive microgels and their interactions with lysozyme.

Microgels composed of carboxymethyl cellulose (CMC) polymers via chemical crosslinking with sodium trimetaphosphate were synthesized and characterized using thermogravimetric analysis (TGA), swelling, and rheological analysis. The effects of pH, ionic strength, and crosslinking density on lysozyme loading in microgels were also studied. The microgel particle size ranged primarily from 10 to 20 μm. TGA revealed that the crosslinking increased the thermal stability of CMC. The swelling degree increased as pH increased from 3 to 5, and remained almost constant from pH 5 to 8. However, the swelling degree decreased with increasing ionic strength. The rheological analysis was in good agreement with the results of swelling degree. The protein uptake decreased with increasing ionic strength and crosslinking density. The pH 6 was the optimal pH for lysozyme absorption at ionic strength 0.05 M. The lysozyme-microgel complex was identified by confocal laser scanning microscopy, and the lysozyme distribution in the microgel was observed to be rather homogeneous.

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.

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.

Modelling and optimisation of enzymatic extrusion pretreatment of broken rice for rice wine manufacture

The manufacture of Chinese rice wine involves an uneconomical, time-consuming, and environmentally unfriendly pretreatment process. In this study, the enzymatic extrusion of broken rice was applied to the brewing of rice wine. The response surface methodology was used to study the effects of the barrel temperature (BT), moisture content (MC), and amylase concentration (AC) on the alcohol yield. A second-order polynomial model had a good fit to the experimental data and the coefficient of determination (R(2)) was 0.9879. According to the model, the optimal parameters required to obtain the highest alcoholic degree of 17.94% were: BT=100.14°C, MC=43%, and AC=1.45‰. Under these optimal conditions, the alcoholic degree actually reached 18.3%, which was close to the value predicted by the model. Enzymatic extrusion improved the yeast growth and alcohol yield during the fermentation process. The fermentation recovery and efficiency of processed rice wine were 38.07% and 94.66%, respectively.

Interaction between amylose and 1-butanol during 1-butanol-hydrochloric acid hydrolysis of normal rice starch

The aim of this study was to examine the interaction between amylose and 1-butanol during the 1-butanol-hydrochloric acid (1-butanol-HCl) hydrolysis of normal rice starch. The interaction model between amylose and 1-butanol was proposed using gas chromatography-mass spectrometry (GC-MS), (13)C cross polarization and magic angle spinning NMR analysis ((13)C CP/MAS NMR), differential scanning calorimetry (DSC), and thermalgravimetric analysis (TGA). GC-MS data showed that another form of 1-butanol existed in 1-butanol-HCl-hydrolyzed normal rice starch, except in the form of free molecules absorbed on the starch granules. The signal of 1-butanol-HCl-hydrolyzed starch at 100.1 ppm appeared in the (13)C CP/MAS NMR spectrum, indicating that the amylose-1-butanol complex was formed. DSC and TGA data also demonstrated the formation of the complex, which significantly affected the thermal properties of normal rice starch. These findings revealed that less dextrin with low molecular weight formed might be attributed to resistance of this complex to acid during 1-butanol-HCl hydrolysis.

Preparation, characterization, and in vitro release of carboxymethyl starch/β-cyclodextrin microgel–ascorbic acid inclusion complexes

Carboxymethyl starch (CMS)/β-cyclodextrin (β-CD) microgels have been synthesized. The percentages of effective β-CD in the microgels have been determined by measuring the amount of iodine retained in its hydrophobic cavity. A microgel–ascorbic acid inclusion complex has been prepared and characterized by Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). In vitro release of ascorbic acid from the microgel has been investigated. Most of the microgel particles had diameters distributed between 10 and 25 μm. The effective β-CD contents in microgels with weight ratios Rβ-CD/CMS of 0.05, 0.1, 0.2, and 0.4 were 1.04, 2.27, 3.96, and 4.12%, respectively. The ascorbic acid loading of the microgels increased as ascorbic acid concentration was increased, but the encapsulation efficiencies of the microgels decreased with increasing its concentration. FTIR and DSC data demonstrated the formation of a microgel–ascorbic acid inclusion complex. In vitro release results indicated that the CMS/β-CD microgels may potentially be applied as a carrier system to prevent the early release of ascorbic acid in the stomach and target its delivery to the intestine.

Effective production of resistant starch using pullulanase immobilized onto magnetic chitosan/Fe3O4 nanoparticles

In this study, pullulanase was firstly immobilized by covalent bonding onto chitosan/Fe3O4 nanoparticles or encapsulation in sol-gel after bonding onto chitosan/Fe3O4 nanoparticles, and then the immobilized pullulanase was used for the effective production of resistant starch (RS). The highest RS content (35.1%) was obtained under the optimized condition of pH 4.4, enzyme concentration of 10ASPU/g and hydrolysis time of 12h when debranched by free pullulsanase, indicating that RS content was significantly (p<0.05) increased when compared to native starch (4.3%) and autoclaved starch (12.5%). Under these conditions, the immobilized pullulanase (10ASPU/g dry starch) yielded higher RS content compared to free enzyme (10ASPU/g dry starch), especially, the pullulanse immobilized by sol-gel encapsulation yielded the highest RS content (43.4%). Moreover, compared to starches hydrolyzed by free pullulanase, starches hydrolyzed by immobilized pullulanase showed a different saccharide profile of starch hydrolysate, including a stronger peak C (MW=5.0×103), as well as exhibited an additional absorption peak around 140°C. Reusability results demonstrated that pullulanase immobilized by sol-gel encapsulation had the advantages of producing higher RS content as well as better operational stability compared to pullulanase immobilized by cross-linking. The resulting enhanced RS content generated by the process described in this work could be used as an adjunct in food processing industries.