Zhengjun Xie

Antioxidant activity of peptides isolated from alfalfa leaf protein hydrolysate.

Alfalfa leaf protein, a potential source of high quality protein for human consumption, was hydrolyzed with protease. Alfalfa leaf protein hydrolysate was fractionated by ultrafiltration and the obtained peptides were purified by dynamical adsorption. The antioxidant activity of alfalfa leaf peptides (ALPs) was investigated and compared with that of a native antioxidant, reduced glutathione (GSH), which was used as a reference. The reducing power of ALPs was 0.69 at 2.00mg/mL. ALPs at 1.60mg/mL and 0.90mg/mL exhibited 79.71% and 67.00% of scavenging activities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and superoxide radical, respectively. In addition, ALPs showed 65.15% chelating effect on ferrous ion at 0.50mg/mL. The molecular weight of the peptides was determined and 67.86% of the total amount was below 1000Da. Combined with the result of the amino acid profiles, ALPs was believed to have high nutritive value in addition to antioxidant activity.

Protective effect of isoflavones from Trifolium pratense on dopaminergic neurons.

In the present study, protective effect of five isoflavones (formononetin, daidzein, pratensein, calycosin and irilone) from Trifolium pratense on lipopolysaccharide-induced dopaminergic neurodegeneration was studied for the first time. The results showed that all five isoflavones attenuated LPS-induced decrease in dopamine uptake and the number of dopaminergic neurons in a dose-dependent manner in rat mesencephalic neuron-glia cultures. Moreover, they also significantly inhibited LPS-induced activation of microglia and production of tumor necrosis factor-alpha, nitric oxide and superoxide in mesencephalic neuron-glia cultures and microglia-enriched cultures. In addition, the rank order of protective potency of five isoflavones was: pratensein>daidzein>calycosin>formononetin>irilone. This study suggested that all five isoflavones protected dopaminergic neurons against LPS-induced injury through inhibition of microglia activation and proinflammatory factors generation.

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.

Development of indirect competitive ELISA and lateral-flow immunochromatographic assay strip for the detection of sterigmatocystin in cereal products

ABSTRACT Sensitive and specific anti-sterigmatocystin (STG) monoclonal antibody (mAb) 4G10 was obtained by immunization and cell fusion. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) method and lateral-flow immunochromatographic assay (ICA) strip method were developed for the detection of STG in cereal products based on this mAb. The 50% inhibition concentration and limit of detection for the ic-ELISA method were 0.092 and 0.015 ng/mL, respectively. The visual limit of detection (vLOD) and cut-off value for the lateral-flow ICA strip method were 0.1 and 0.5 ng/mL, respectively. From the analysis of different cereal samples (wheat, maize and rice), the recovery rates ranged from 78.3% to 122.0% for the ic-ELISA method. For the lateral-flow ICA strip, the vLODs were 3, 1.2 and 3 ng/g, and the cut-off values were 12, 6 and 6 ng/g for wheat, maize and rice, respectively. Therefore, both of the developed methods are suitable for the on-site detection and rapid screening of numerous samples.

Continuous-flow electro-assisted acid hydrolysis of granular potato starch via inductive methodology

The induced electric field assisted hydrochloric acid (IEF-HCl) hydrolysis of potato starch was investigated in a fluidic system. The impact of various reaction parameters on the hydrolysis rate, including reactor number (1-4), salt type (KCl, MgCl2, FeCl3), salt concentration (3-12%), temperature (40-55°C), and hydrolysis time (0-60h), were comprehensively assessed. Under optimal conditions, the maximum reducing sugar content in the hydrolysates was 10.59g/L. X-ray diffraction suggested that the crystallinity of IEF-HCl-modified starches increased with the intensification of hydrolysis but was lower than that of native starch. Scanning electron microscopy indicated that the surface and interior regions of starch granules were disrupted by the hydrolysis. The solubility of IEF-HCl-modified starches increased compared to native starch while their swelling power decreased, contributing to a decline in paste viscosity. These results suggest that IEF is a notable potential electrotechnology to conventional hydrolysis under mild conditions without any electrode touching the subject.

Tuneable surface enhanced Raman spectroscopy hyphenated to chemically derivatized thin-layer chromatography plates for screening histamine in fish

Reliable screening of histamine in fish was of urgent importance for food safety. This work presented a highly selective surface enhanced Raman spectroscopy (SERS) method mediated by thin-layer chromatography (TLC), which was tailored for identification and quantitation of histamine. Following separation and derivatization with fluram, plates were assayed with SERS, jointly using silver nanoparticle and NaCl. The latter dramatically suppressed the masking effect caused by excessive fluram throughout the plate, thus offering clear baseline and intensive Raman fingerprints specific to the analyte. Under optimized conditions, the usability of this method was validated by identifying the structural fingerprints of both targeted and unknown compounds in fish samples. Meanwhile, the quantitative results of this method agreed with those by an HPLC method officially suggested by EU for histamine determination. Showing remarkable cost-efficiency and user-friendliness, this facile TLC-SERS method was indeed screening-oriented and may be more attractive to controlling laboratories of limited resource.

Changes in crystal structure and physicochemical properties of potato starch treated by induced electric field

The effects of induced electric field (IEF) on the crystal structure and physicochemical properties of potato starch were investigated by subjecting identically treated control and electrically-modified samples to the same temperature history. Additionally, a method of combining IEF with heating for efficient modification of native polymer was also proposed. Results showed that the application of IEF at an electric voltage of 75V has a statistically significant effect on starch gelatinization and pasting properties, especially when combined with heating at 50°C. After treatment by the combination method for 96h, the gelatinization temperatures increased, which can be explained by the slight increase in the ratio of 1044/1015cm(-1) and relative crystallinity. Furthermore, IEF reduced granular swelling and therefore contributed to decreasing the peak, breakdown, and setback viscosity of potato starch. This study explores the potential of IEF as innovative technology for starch modification.

Determination of Bisphenol A by a Gold Nanoflower Enhanced Enzyme-Linked Immunosorbent Assay

ABSTRACT The use of nanomaterials to improve the sensitivity of enzyme-linked immunosorbent assays (ELISA) for small molecules allows wider application of this method. In this work, gold nanoflowers were synthesized by a seed-mediated procedure and used to prepare a horseradish peroxidase-immunoglobulin G-gold nanoflower complex. The complex was used as the signal amplification probe in a novel ELISA for bisphenol A. The gold nanoflower-enhanced ELISA demonstrated excellent detection sensitivity of 0.05 ng/mL, which was 20 times more sensitive than a standard ELISA procedure. A linear dynamic range from 0.1 to 5.0 ng/mL was obtained by this approach. The gold nanoflower-enhanced ELISA was used to determine bisphenol A in lake water, with recoveries from 92.0 to 102.0% in samples fortified at concentrations of 0.5, 1.0, and 3.0 ng/mL. The gold nanoflower-enhanced ELISA was shown to offer good sensitivity, simplicity, and low cost.

Development of an immunochromatographic assay for the detection of alternariol in cereal and fruit juice samples

ABSTRACT An immunochromatographic strip was developed for the determination of alternariol (AOH) using both semi-quantitative and quantitative methods based on a sensitive monoclonal antibody we produced. With AOH-spiked samples, the visual limit of detection for cereal and juice were 160 ng/g and 25 ng/mL, and the cut-off values were 640 ng/g and 100 ng/mL, respectively. For quantitative analysis based on a strip scan reader, the calculated limit of detection was 15.5–19.4 ng/g for cereal and 2.8–3.5 ng/mL for fruit juice. The recovery rates ranged from 116% to 125%, and 113% to 123%, respectively. Therefore, this method was effective for AOH detection and suitable for on-site detection and rapid screening of samples.

Highly sensitive and selective colorimetric detection of Hg2+ based on the separation of Hg2+ and formation of catalytic DNA–gold nanoparticles

Hg2+ ions can be absorbed onto a DNA–AuNP complex and separated from water samples while the catalytic activity of DNA–AuNPs can be promoted. Based on the above principle, a highly sensitive and selective colorimetric assay for the detection of Hg2+ was developed. The proposed method for Hg2+ has a detection limit of 1.5 nM with a linear range from 5.0 nM to 500 nM. Moreover, this detection method for Hg2+ demonstrated more than 1000-fold selectivity toward most of the possible interfering ions and can be used for tap water detection. The results indicate the high potential of AuNPs as an enzyme mimic for sensing heavy metal ions by metallophilic interactions.