Fluorescently labeled starch nanocrystal (FL-SNC) was synthesized using a simple, low-cost, and scalable two-step chemical modification process. Reactive amino groups were introduced onto the SNC surface through silanization with 3-aminopropyl triethoxysilane (APTES), and fluorescein isothiocyanate (FITC) groups were covalently attached through thiourea. Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, solid-state cross-polarization magic-angle spinning 13C NMR, UV–visible absorbance spectrophotometry, and fluorescence emission spectroscopy confirmed the successful introduction of the fluorescent groups. Transmission electron microscopy and X-ray diffraction data indicated that the dispersibility of FL-SNC was significantly improved, and the original crystallinity and morphology were retained. Compared with a mixture of uncoupled FITC and SNC, covalently connected FL-SNC displayed a more obvious fluorescence intensity and higher photostability. Furthermore, FL-SNC was biocompatible with cells and could be easily internalized. In combination with the participation of active hydroxyls, this facile approach has potential use for synthesis of fluorescently polyhydroxyl nanoparticles and can be widely used for making biosensors and biomarker in food and biomedical industries.Keywords: Fluorescein isothiocyanate; Fluorescent labeling; Starch nanocrystal; Surface modification; Triethoxysilane;

•The distribution of chitosan in the microgels was identified by confocal laser scanning microscopy.•The optimal molecular weight of chitosan was 100 kDa.•The optimal weight ratios of chitosan and carboxymethyl starch to microgels were 0.1 and 0.06, respectively.•In vitro release of lysozyme from stabilized microgels was investigated.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 100 kDa, 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.

•Fluorescent probes were successfully encapsulated in the helix cavity of HAMS.•Salicylic acid (SA) was chosen as the most suitable fluorescent probe.•The starch-SA inclusion complex indicated an increasing fluorescence.•The capability of maize starches to form inclusion complexes was evaluated.In this study, high-amylose maize starch (HAMS) was mixed with salicylic acid, 1-naphthol, and 2-naphthol, and the physical mixtures were then subjected to a sealed-heating procedure to prepare HAMS-fluorescence guest complexes. The results, obtained from wide angle X-ray scattering and thermogravimetric analysis, showed that all three fluorescence guests were encapsulated in the hydrophobic cavity of HAMS. After screening, salicylic acid was chosen as the most suitable fluorescent probe for evaluating the properties of the starch helix cavity. The formation of a starch-salicylic acid inclusion complex was accompanied by increased fluorescence from the salicylic acid molecules included in the complex. The hydrophobicity of the starch helix cavity and the capability of starch to form inclusion complexes could be evaluated from the increasing intensity of the fluorescence. Accordingly, the capabilities of maize starches to form inclusion complexes followed the order: high-amylose maize starch > normal maize starch > waxy maize starch.Download high-res image (195KB)Download full-size image

•Gradient PEG6000 precipitation was used to fractionate dextrin.•The average dispersity was established to assess the fractionation effect.•A dextrin concentration range of 0.9%–3.6% did not affect the fractionation effect.•This method was applicable in acidic, neutral, and alkaline environments.•A weakly alkaline environment was optimal for dextrin fractionation.Polyethylene glycol (PEG) was further applied for fractionating dextrin prepared from cassava starch. The initial dextrin concentration and pH of the dextrin solutions were crucially considered in this study with the average molecular-weight dispersity (DMa) as the index. The results showed that the initial dextrin concentration significantly affected the mass fraction and the molecular weight distribution of each dextrin fraction obtained from gradient PEG precipitation. However, the initial dextrin concentration, which ranged from 0.9% to 3.6%, did not affect the DMa of the dextrin fractions. Furthermore, the DMa of the fractions obtained at pHs 4.00, 4.96, 6.00, 6.92, 7.99, 8.96, and 9.91, was 1.364, 1.341, 1.305, 1.286, 1.273, 1.311, and 1.404, respectively, while the dispersity of the parent dextrin was 2.052. These results suggest that the preparative approach, gradient PEG precipitation, is applicable in acidic, neutral, and alkaline environments, and that a weakly alkaline environment is optimal for dextrin fractionation.

•Gradient PEG precipitation was established to fractionate dextrin.•PEG6000 was the most suitable to fractionate the parent dextrin.•Narrowly-distributed PEG should be selected to obtain a superior result.•An average dispersity was established to assess the fractionation effects.This work aimed at developing a novel approach, named gradient polyethylene glycol (PEG) precipitation, to fractionate dextrin into fractions with narrower molecular weight distribution. This approach was based on the incompatibility between PEG and dextrin in aqueous solution; this incompatibility is positively correlated with the molecular weight of dextrin. Theoretically, dextrin can be precipitated in descending order of molecular weight by the gradual addition of PEG into the dextrin solution. Specifically, this study investigated the effects of molecular weight and its distribution of PEG on dextrin fractionation with the molecular-weight dispersity (DM) as index. The parent dextrin could be fractionated by PEG into several fractions with different molecular weights and lower DM. The average DM of fractions obtained by PEG2000, PEG4000, PEG6000, PEG10000, and PEG20000 was 1.471, 1.352, 1.286, 1.453, and 2.028, respectively, while the DM of the parent dextrin was 2.052. These data suggest that PEG6000 was the optimal precipitant, while PEG20000 was unsuitable for fractionating dextrin. Furthermore, narrowly-distributed PEG resulted in optimum fractionation results. Therefore, gradient PEG precipitation is an efficient method for fractionating dextrin. Additionally, narrowly-distributed PEG of suitable molecular weight should be selected to obtain superior fractionation results.

•Thermal properties of starch nanocrystal were mostly preserved after oxidation.•There were adjacent two-step degradation processes for SNC and OSNC.•Oxidation induced the increase of char content.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 0.091 mmol/g to 0.033 and 0.129 mmol/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.

•Inhibitory effects of four industrial tea derivatives on wheat starch retrogradation were compared.•Inhibition of wheat starch retrogradation by tea derivatives was investigated by TPA, RVA and DSC.•The retrogradation kinetics of the starch additive mixtures were well modeled by the Avrami theory.The effect of four industrial tea derivatives (tea polyphenols [TPS], tea water-soluble extracts [TSE], tea polysaccharides [TSS], and green tea powder [GTP]), on the retrogradation of wheat starch was investigated using texture profile analysis (TPA), differential scanning calorimetry (DSC), rapid viscosity analysis (RVA), and the α-amylase–iodine method. The addition of the four tea derivatives resulted in decreased hardness and increased cohesiveness of the starch gel as shown by the TPA test. The DSC data demonstrated an increase in the enthalpy change of starch gelatinization and a decrease in the enthalpy change of starch recrystallite dissociation. The RVA results indicated that the peak viscosity, representing the intermolecular forces of wheat starch, was reduced after addition of TPS, TSE, and TSS, respectively, but was increased by GTP. Furthermore, the half crystallization time in the Avrami equation almost doubled after the separate addition of the tea derivatives.

•CMS microgels with different crosslinking densities were synthesized.•Microgels were characterized by FT-IR, TGA, and rheological analyses.•Swelling degree of microgels was measured as a function of pH and ionic strength.•Absorption of lysozyme by microgels was driven by electrostatic interaction.•The lysozyme–microgels complex formed was identified by CLSM.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 25 μm to 45 μm. 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.

•Gradient alcohol precipitation was established to fractionate dextrin.•The effect of the alcohol type on fractionation was studied.•The effect of the initial dextrin concentration on fractionation was studied.•Dispersity was used for evaluating the fractionation effect.Gradient alcohol precipitation was established as a fractionation method, and used for fractionating the 1-butanol-HCl-hydrolyzed cassava starch into dextrin fractions with a narrower molecular weight distribution. The addition of alcohol may have led to very high alcohol concentration in some parts of the dextrin solution, which may have impeded the fractionation process. Therefore, the rate of alcohol addition should be rigorously controlled during fractionation. The effects of the alcohol type and the initial dextrin concentration on fractionation were studied using the molecular-weight dispersity (DM) as index. The parent dextrin was fractionated by gradient alcohol precipitation into seven fractions with decreasing DM, with the volume ratios of the dextrin solution to alcohol at 4:1, 2:1, 1:1, 1:2, 1:3, 1:4, and 1:5, respectively. The better fractionation effect of different alcohols was in the order of methanol > ethanol > isopropanol; whereas the dextrin yield by these alcohols was in the reverse order. Furthermore, the peak molecular weight of each fraction tended to decrease with an increase in the alcohol concentration at which it was precipitated. The optimal initial concentration was in the range of 1.8%–2.7%, and lower or higher concentrations resulted in inferior fractionation. These results suggest that gradient alcohol precipitation is an efficient method for fractionating dextrin into fractions with different molar masses of low DM, which would allow dextrin fractions to be tailor-made for specific application.Graphical abstractThe solubility of dextrin was inversely proportional to its molecular weight. Therefore, the dextrin was gradually precipitated in the descending order of molecular weight through gradually adding alcohol into the dextrin solution. Triangle represented alcohol; circles of different sizes represented dextrin of different sizes.

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.

•HHP improves the percentage of slowly digestible starch.•HHP increases the imperfect crystallites in the HHP-gelatinized starch.•HHP reduces the retrogradation of rice starch.•Enthalpy change of retrogradation is not positively correlated with the SDS percentage.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.

•Dextrin monosuccinate with the maximum DS = 2.64 was synthesized.•DMSO was more efficient than DMF for preparing dextrin monosuccinate.•Dextrin monosuccinate was identified by FT-IR and 13C NMR.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 13C NMR. The FT-IR data indicated the absorption bands of esters and carbonyl acids at 1726 and 1574 cm−1. Signals at 173.13, 171.81, 28.79, and 28.61 ppm in 13C 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.

Broken rice, pretreated by enzymatic extrusion liquefaction, was used to produce Chinese rice wine by simultaneous saccharification and fermentation (SSF) process in this study. The study compared the novel process and traditional process for Chinese rice wine fermentation utilizing broken rice and head rice, respectively. With the optimum extrusion parameters (barrel temperature, 98 °C; moisture content, 42 % and amylase concentration, 1 ‰), 18 % (v/v at 20 °C) alcoholic degree, 37.66 % fermentation recovery and 93.63 % fermentation efficiency were achieved, indicating enzymatic extrusion-processed rice wine from broken rice exhibited much higher fermentation rate and efficiency than traditional-processed rice wine from head rice during SSF. The starch molecule distribution data indicated that the alcoholic degree was related to the oligosaccharides’ formation during enzymatic extrusion. Sum of amino acid (AA) in the extrusion-processed wine was 53.7 % higher than that in the traditional one. These results suggest that the enzymatic extrusion pretreatment for broken rice is a feasible and alternative process in the fermentation of Chinese rice wine.

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.Highlights► A HHP method was designed to prepare β-CD-Vc inclusion complex. ► HHP effectively promoted the formation of the β-CD-Vc inclusion complex. ► The β-CD-Vc inclusion complex was identified by FI-IR, UV–vis and DSC.

An approach mainly based on thermogravimetric analysis (TGA) was developed to evaluate the stoichiometric ratio (SR, guest to host) of the guest–α-cyclodextrin (Guest-α-CD) inclusion complexes (4-cresol-α-CD, benzyl alcohol-α-CD, ferrocene-α-CD and decanoic acid-α-CD). The present data obtained from Fourier transform-infrared (FT-IR) spectroscopy showed that all the α-CD-based inclusion complexes were successfully prepared in a solid-state form. The stoichiometric ratios of α-CD to the relative guests (4-cresol, benzyl alcohol, ferrocene and decanoic acid) determined by the developed method were 1:1, 1:2, 2:1 and 1:2, respectively. These SR data were well demonstrated by the previously reported X-ray diffraction (XRD) method and the NMR confirmatory experiments, except the SR of decanoic acid with a larger size and longer chain was not consistent. It is, therefore, suggested that the TGA-based method is applicable to follow the stoichiometric ratio of the polycrystalline α-CD-based inclusion complexes with smaller and shorter chain guests.Highlights► We develop a TGA method for the measurement of the stoichiometric ratio. ► A series of formulas are deduced to calculate the stoichiometric ratio. ► Four α-CD-based inclusion complexes were successfully prepared. ► The developed method is applicable.

⿢Starch was pre-gelatinized in [BMIm]Cl and bio-esterified with OSA in [OMIm]NO3.⿢[BMIm]Cl was excellent solvent for starch dissolution.⿢Ionic liquid was confirmed to be feasible solvent for starch bio-modification.⿢Bio-esterification conditions were optimized.Biosynthesis of octenyl succinic anhydride (OSA) starch was investigated using ionic liquids (ILs) as reaction media. Waxy maize starch was pretreated in 1-butyl-3-methylimidazolium chlorine and then esterified with OSA in 1-octyl-3-methylimidazolium nitrate by using Novozyme 435 as catalyst. The degree of substitution of OSA starch reached 0.0130 with 5 wt% starch concentration and 1 wt% lipase dosage based on ILs weight at 50 °C for 3 h. The formation of OSA starch was confirmed by fourier transform infrared spectroscopy. Scanning electron microscopy and X-ray diffraction revealed that the morphology and crystal structure of starch were significantly destroyed. Thermogravimetric analysis showed that esterification decreased the thermal stability of starch. The successful lipase-catalyzed synthesis of OSA starch in ILs suggests that ILs are potential replacement of traditional organic solvents for starch ester biosynthesis.Download high-res image (149KB)Download full-size image