Daodong Pan

Rolling chain amplification based signal-enhanced electrochemical aptasensor for ultrasensitive detection of ochratoxin A.

A novel electrochemical aptasensor is described for rapid and ultrasensitive detection of ochratoxin A (OTA) based on signal enhancement with rolling circle amplification (RCA). The primer for RCA was designed to compose of a two-part sequence, one part of the aptamer sequence directed against OTA while the other part was complementary to the capture probe on the electrode surface. In the presence of target OTA, the primer, originally hybridized with the RCA padlock, is replaced to combine with OTA. This induces the inhibition of RCA and decreases the OTA sensing signal obtained with the electrochemical aptasensor. Under the optimized conditions, ultrasensitive detection of OTA was achieved with a limit of detection (LOD) of 0.065 ppt (pg/mL), which is much lower than previously reported. The electrochemical aptasensor was also successfully applied to the determination of OTA in wine samples. This ultrasensitive electrochemical aptasensor is of great practical importance in food safety and could be widely extended to the detection of other toxins by replacing the sequence of the recognition aptamer.

Functional graphene-gold nano-composite fabricated electrochemical biosensor for direct and rapid detection of bisphenol A.

In this research, the graphene with excellent dispersity is prepared successfully by introducing gold nanoparticle to separate the individual sheets. Various techniques are adopted to characterize the prepared graphene and graphene-gold nanoparticle composite materials. This fabricated new composite material is used as the support material to construct a novel tyrosinase based biosensor for detection of bisphenol A (BPA). The electrochemical performances of the proposed new enzyme biosensor were investigated by differential pulse voltammetry (DPV) method. The proposed biosensor exhibited excellent performance for BPA determination with a wide linear range (2.5×10(-3)-3.0 μM), a highly reproducible response (RSD of 2.7%), low interferences and long-term stability. And more importantly, the calculated detection limit of the proposed biosensor was as low as 1 nM. Compared with other detection methods, this graphene-gold nanoparticle composite based tyrosinase biosensor is proved to be a promising and reliable tool for rapid detection of BPA for on-site analysis of emergency BPA related pollution affairs.

Antioxidant and immunomodulatory activity of selenium exopolysaccharide produced by Lactococcus lactis subsp. lactis.

Exopolysaccharide (EPS) was isolated and purified from Lactococcus lactis subsp. Lactis culture broth. Selenium chloride oxide (SeCl(2)O) was added to the EPS to synthesize selenium-exopolysaccharide (Se-EPS). The in vitro and in vivo antioxidant and in vivo immunomodulatory activity of EPS and Se-EPS were compared. EPS and Se-EPS scavenged superoxide anions and hydroxyl radicals. They also increased catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, while decreasing malondialdehyde (MDA) levels in serum and in the livers of mice. Se-EPS showed stronger in vitro and in vivo antioxidant activity than were shown by EPS. The in vivo immunoenhancement activity of EPS and Se-EPS induced by cyclophosphamide (CY) treatment in immunosuppressed mice was researched. EPS and Se-EPS treatments increased macrophage phagocytosis, spleen and thymus indices and haemolytic complement activity (HC(50)). Se-EPS showed stronger immunomodulatory activity than did EPS.

The probiotic properties of Lactobacillus buchneri P2

Aims:  To isolate new lactobacilli strain with cholesterol‐lowering effect and analyse its probiotic properties and possible mechanisms of cholesterol removal.

Volatile organic compounds profile during milk fermentation by Lactobacillus pentosus and correlations between volatiles flavor and carbohydrate metabolism

Flavor, as one of the most important properties determining the acceptability and preference of fermented milks, is influenced by compositional and processing factors. In this study, we focused on the volatile organic compounds related to flavor during milk fermentation by Lactobacillus pentosus according to electronic nose analysis. Xylose (1% addition) metabolized by Lb. pentosus strongly affects the flavor of yogurt, with the potent volatile organic compounds of ethanol (3.08%), 2,3-butanedione (7.77%), and acetic acid (22.70%) detected using solid-phase microextraction coupled with gas chromatography-mass spectrometry analysis. Sensoryanalysis also showed skimmed yogurt fermented by Lb. pentosus with 1% xylose had the unique scores of sourness (acetic acid) and butter flavor (2,3-butanedione). Furthermore, α-acetolactate synthase and α-acetolactate decarboxylase in carbohydrate metabolism play important roles in milk fermentation. Under preferable conditions (pH 5.5, 42 °C) for α-acetolactate synthase and α-acetolactate decarboxylase, the relative content of potent flavor compound 2,3-butanedione was 10.13%, which was 2.55% higher than common culture condition (pH 4.5, 37 °C), revealing that xylose metabolized by Lb. pentosus has potential values for the milk product industry, such as the acceptability and preference of fermented milk product.

Effect of black pepper essential oil on the quality of fresh pork during storage.

The effect of different concentrations (0, 0.1 and 0.5%, v/v) of black pepper essential oil (BPEO) on thiobarbituric acid reactive substances (TBARS), meat color, the percentage of metmyoglobin (MetMb%), microbiological parameters and total volatile basic nitrogen (TVB-N) of pork loins stored at 4°C for 9days was evaluated. BPEO treatments showed lower TBARS, MetMb%, yellowness (b*) values, Pseudomonas spp. and Enterobacteriaceae count and TVB-N values and higher lightness (L*) and redness (a*) values than the control during storage; the effectiveness of BPEO was dose-dependent. The retardation of the formation of MetMb by adding BPEO ensured higher L* and a* values and lower b* values than the control at 6 and 9days; the MetMb content has a similar trend to the lipid oxidation. The lower TVB-N value of BPEO treatments than the control could be attributed to the inhibition of Pseudomonas spp. and Enterobacteriaceae. Gram-negative bacteria were more sensitive than Gram-positive bacteria to BPEO.

Structure and anti-inflammatory capacity of peptidoglycan from Lactobacillus acidophilus in RAW-264.7 cells.

Probiotic bacteria, especially the Lactobacillus species, can potentially play a significant role in the antiviral and antimicrobial activity of a hosts immune system. Lactobacillus acidophilus, an intestinal bacterium, is involved in the intestinal epithelial cell response when a pathogen adheres to a cell. In this study, the structure of peptidoglycan (PGN) isolated from L. acidophilus was determined with the help of HPLC, NMR, FT-IR and MALDI-TOF/TOF MS. The molecular mass of PGN is 875.260 Da. The anti-inflammatory capacity of PGN was evaluated in model RAW 264.7 cells. Epifluorescence microscopy images and western blot analysis provided compelling evidence of PGNs anti-inflammatory capacity on LPS-induced macrophages. A significant decrease in inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) levels when PGN was added up to 200 μg/ml. These data provide new insight into the cellular and molecular mechanisms by which probiotic bacteria can contribute to maintaining good health.

Effect of trypsin treatments on the structure and binding capacity of volatile compounds of myosin.

In order to investigate the mechanism between flavor binding and proteins degradation during meat processing, the influence of different trypsin contents on the structure of myosin and the adsorption capacity on aldehydes and ketones was determined. The 1% treatment produced subfragment 2 (S2), light meromyosin (LMM) and decreased 18 and 16kDa light chains; 5% and 10% treatments produced 100 and 65kDa new bands and more S2, LMM and cleaned light chains. With the rising trypsin contents, β-sheet, β-turn, random coil, hydrophobicity and total sulfydryl content increased; solubility, α-helix and free percentages of aldehydes and ketones decreased. The increase of absorbing capacity could be attributed to the increased hydrophobicity and total sulphydryl and the unfolding of secondary structures by exposing reactive amino and thiol groups and hydrophobic sites; the decreased solubility was related to the increased hydrophobicity. The trypsin-dose dependent proteolysis of myosin increased the retention of volatile compounds.

Activation of caspase-9 and its influencing factors in beef during conditioning.

To study the activation of caspase-9 and its potential influence in conditioning, longissimus thoracis (LT), semitendinosus (STN) and psoas minor (PMi) muscles were used to analyze the ratio of pro-apoptotic bax to anti-apoptotic bcl-2 in fresh tissues and observe the changes in ATP, cytosolic cytochrome c and caspase-9 activity levels during storage at 4°C. Caspase-9 activity at 5 h is higher than the activity at 0 and 24 h in the muscles (P<0.001). The ATP content decreased between 0 and 3 h, between 8 and 14 h in the PMi and LT muscles (P<0.0001), whereas between 0 and 5 h, between 8 and 14 h in the STN muscle (P<0.0001). There is 60.2%, 55.3% and 43.1% available ATP in the STN, LT and PMi muscles at 5 h, respectively. The cytosolic cytochrome c level increased during 5 and 24 h storage in the LT and PMi muscles (P<0.0001), during 5 and 96 h in the STN muscle (P<0.0001). The cytosolic cytochrome c at 24 h (P<0.001) and ratio of bax to bcl-2 (P<0.05) was higher in the PMi than in other muscles. We concluded that the increase in cytosolic cytochrome c and available intracellular ATP should be responsible for the increase in caspase-9 activity; the activation of caspase-9 could be limited by the subsequent depletion of ATP; the postmortem release level of cytochrome c could be determined by the ratio of bax to bcl-2 in fresh tissues.

A sensitive colorimetric aptasensor for chloramphenicol detection in fish and pork based on the amplification of a nano-peroxidase-polymer

A novel colorimetric aptasensor was developed for sensitive and selective determination of chloramphenicol (CAP) based on gold nanoparticles (AuNPs) labeled with Power Vision (PV) and magnetic separation. PV, with a high enzyme-to-antibody ratio, is composed of a compact enzyme-linker antibody conjunction. In this assay, an aptamer of CAP was immobilized on Fe3O4@Au magnetic nanoparticles as a capture probe (AuMNPs–Apt) to concentrate target CAP. The complementary DNA (cDNA) and PV were both labeled on AuNPs to form a nano-peroxidase polymer as a signal tag (cDNA–AuNPs–PV). And the special tags could hybridize with the aptamer and cDNA to form AuMNP–Apt/cDNA–AuNP–PV conjugates. In the presence of CAP, the aptamer preferentially bound to CAP and caused the dissociation of some cDNA–AuNPs–PV on the conjugates with magnetic separation. PV, carried on signal tags, could greatly catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) leading to color development, which could be quantified by Ultraviolet-visible (UV-vis) spectroscopy. A linear response to CAP concentration in the range of 0.05–200 ng mL−1 was obtained by this proposed method, with a low detection limit down to 0.02 ng mL−1. Besides, this assay was successfully employed to analyze CAP in fish and pork samples, whose results were consistent with those of the conventional enzyme-linked immunosorbent assay (ELISA) method.