NMR Immunosensor Based on a Targeted Gadolinium Nanoprobe for Detecting Salmonella in Milk.

Detecting harmful pathogens in food is not only a crucial aspect of food quality management but also an effective way to ensure public health. In this paper, a complete nuclear magnetic resonance biosensor based on a novel gadolinium (Gd)-targeting molecular probe was developed for the detection of Salmonella in milk. First, streptavidin was conjugated to the activated macromolecular polyaspartic acid (PASP) via an amide reaction to generate SA-PASP. Subsequently, the strong chelating and adsorption properties of PASP toward the lanthanide metal gadolinium ions were exploited to generate the magnetic complex (SA-PASP-Gd). Finally, the magnetic complex was linked to biotinylated antibodies to obtain the bioprobe and achieve the capture of Salmonella. Under optimal experimental conditions, the sensor we have constructed can achieve a rapid detection of Salmonella within 1.5 h, with a detection limit of 7.1 × 103 cfu mL-1.

Rapid detection of Salmonella in milk by labeling-free electrochemical immunosensor based on an Fe3O4-ionic liquid-modified electrode.

Electrochemical sensors show distinct advantages over other types of sensors in the rapid detection of microorganisms. Here, we attempted to construct a label-free electrochemical immunosensor based on an Fe3O4-ionic liquid (IL)-modified electrode to rapidly detect Salmonella in milk. The excellent ionic conductivity of the IL facilitated sensor construction, and the large surface area of nano-Fe3O4 provided numerous sites for subsequent experiments. An antibody was fixed on the Fe3O4-IL complex with polyglutamic acid modification by a simple infusion method. The microstructure of the Fe3O4-IL composites was investigated by scanning electron microscopy, and the elements and structures of the composites were analyzed by energy dispersive X-ray and Fourier transform infrared spectroscopy. Under optimized experimental conditions, the detection range of the constructed sensor was 3.65 × 102-3.65 × 108 CFU mL-1, and the LOD was 1.12 × 102 CFU mL-1 (S/N = 3). In addition, the prepared electrochemical immunosensor is convenient for detecting foodborne pathogens because of its outstanding stability, good selectivity, and repeatability.

Study on the effect of different concentrations of choline glycine ionic liquid-water mixtures on debranched starch butyrylation reaction.

In this study, the effect of choline glycine ionic liquids on the butyrylation of starch was investigated by the butyrylation of debranched cornstarch in different concentrations of choline glycine ionic liquid-water mixtures (choline glycine ionic liquids to water in mass ratios of 0:10, 4:6, 5:5, 6:4, 7:3, 8:2 and 10:0). The butyryl characteristic peaks in 1H NMR and FTIR of the butyrylated samples indicated the success of butyrylation modification. 1H NMR calculations showed that the most effective mass ratio of choline glycine ionic liquids to water (6:4) increased the butyryl substitution degree from 0.13 to 0.42. X-ray diffraction results showed that the crystalline type of the starch modified in the choline glycine ionic liquid-water mixtures changed from B-type to a mixture of V-type and B-type isomers. The butyrylated starch modified in the ionic liquid increased its own content of resistant starch from 25.42 % to 46.09 %. This study highlights the effect of different concentrations of choline glycine ionic liquid-water mixtures on the promotion of starch butyrylation reactions.

Potential allergenicity and hydrolysis assessment of bovine casein and ß-casein by treatment with lactic acid bacteria.

Casein is one of the main allergens in cow's milk, accounting for 80% of cow's milk proteins. The ability of hydrolyzing proteins by bacteria is also different. In this study, the capacity of lactic acid bacteria to hydrolyze casein or ß-casein and the IgG/IgE-binding capacity of hydrolysates were evaluated. The intensity of casein and ß-casein degradation was analyzed by SDS-PAGE and RP-HPLC. The hydrolysates were tested for their capacity to inhibit IgG and IgE binding by ELISA. The peptides in the hydrolysate were also analyzed by LC-MS/MS. In these strains, Lactobacillus rhamnosus (CICC No. 22175) had the strongest hydrolysis of casein and ß-casein. The hydrolysate of Lactobacillus rhamnosus (CICC No. 22175) showed the lowest antigenicity and potential allergenicity. It also hydrolyzed major allergen IgE epitopes and preserved T cell epitopes. Thereore Lactobacillus rhamnosus (CICC No. 22175) could be used for developing hypoallergenic dairy products and the development of tolerance. PRACTICAL APPLICATIONS: By the study, it obtained that a strain of Lactobacillus rhamnosus could effectively degrade casein and reduced the potential allergenicity of casein. At the same time, some major allergic epitopes were hydrolyzed and T cell epitopes were preserved. Therefore, it is very valuable for the application and development of lactic acid bacteria. The hydrolysate can also be used in a new hypoallergenic dairy formula with specific health benefits and promoting oral tolerance.

The mechanism of delaying starch digestion by luteolin.

In this study, the mechanisms of the delay of starch digestion by luteolin were revealed by studying the luteolin-PPA (porcine pancreatic α-amylase) interaction and luteolin-starch interaction. The luteolin-PPA interaction was investigated by inhibitory kinetics analysis, fluorescence quenching, circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy and molecular docking. The results of the inhibitory kinetics revealed that luteolin was a mixed-type inhibitor of PPA and that the inhibitory action was reversible. Fluorescence spectroscopy (including fluorescence quenching and thermodynamics) and molecular docking analyses indicated that hydrogen bonds and hydrophobic forces were the main forces between PPA and luteolin. CD and FT-IR spectroscopy analyses showed that the interaction between luteolin and PPA changed the secondary structure of PPA and induced a decline in its activity. In addition, the luteolin-starch interaction was also studied using UV-visible absorption and X-ray diffraction analyses. These indicated that luteolin could bind with PPA, and that hydrogen bonds and van der Waals forces may be present. Overall, luteolin delayed starch digestion not only by binding with PPA but also by binding with starch. Thus, luteolin has the potential to prevent and control diabetes by being added into starch-based food to delay starch digestion.

Changes in lipid properties of duck egg yolks under extreme processing conditions.

The changes in lipid properties of duck egg yolks during processing may affect the quality of egg yolks. In this paper, various physicochemical and instrumental methods were used to study the changes of lipid characteristics of duck egg yolks under extreme processing conditions such as high salt, high salt-heat synergy and strong alkali. The results showed that both the high salt and high salt-heat treatments resulted in the decrease of the moisture content and the increase of the oil exudation of egg yolks. The iodine value of the lipid extracted from salted egg yolks with or without heat treatment decreased. However, strong alkali treatment increased the moisture content of egg yolks, and the oil exudation increased at first and then decreased. The iodine value of the lipid obtained from preserved egg yolks showed an overall trend with first increase and then decrease, and the saponification value of the lipid got from preserved egg yolks was lower than the lipid got from the raw salted egg yolks. According to the conjugated diene acid value and thiobarbituric acid value, the lipid of egg yolks was oxidized to different degrees under the three processing conditions. At the end of pickling, the fatty acid content of the lipid acquired from egg yolks all increased. Therefore, all three extreme treatments significantly changed the lipid properties of duck egg yolks.

Effects of packaging methods on the quality of heavy metals-free preserved duck eggs during storage.

Preserved eggs without adding heavy metals in the pickling solution (heavy metals-free preserved eggs) have been developed, but it was found that the undesirable phenomenon such as dry shrinkage and fading occurred when they were not packaged and stored at room temperature. In this study, the effects of 5 packaging methods on the quality of heavy metals-free preserved eggs during storage were systematically studied. These methods included storage at room temperature and 4°C without packaging, wrapping with plastic bags, paraffin coating, and vacuum package. Through adopting these 5 packaging methods, the results showed that the moisture content and pH of the albumen decreased continuously, the mass loss rate increased continuously, the content of total volatile basic nitrogen increased firstly and then decreased, and the albumen hardness increased continuously. No microorganisms were detected in all samples with the 5 packaging methods during storage. Among them, the uncoated preserved eggs suffered the most serious moisture loss and mass loss, and the pH dropped at the fastest rate, followed by the preserved eggs wrapped in plastic bags. Preserved eggs stored at low temperature tended to turn yellow during storage, and the albumen showed higher hardness. The packaging method of paraffin coating performed the best in preventing the moisture loss of the albumen and the weight loss, which only decreased by 0.34 and 1.24%, respectively, after 3 mo. The best springiness, the darkest color, and the highest sensory score were found in the vacuum-packed preserved eggs after 3 mo of storage. It was concluded that paraffin coating and vacuum packing had better effect, while plastic bag packing showed the worst preservation performance for heavy metals-free preserved eggs.

Gelation behavior of egg yolk under physical and chemical induction: A review.

Gelation is one of the most important functional properties of egg yolk. High content and rich variety of protein and lipid in egg yolk are the material basis of gel formation. The natural structure of proteins in egg yolk is unfolded under treatments such as heat, alkali, salt, etc., thus causing the interactions between protein-protein and protein-lipid and forming the gel. Under different methods of induction, egg yolk is solidified to form different three-dimensional network structures. Different inducing methods exhibit different gel formation mechanisms. In this paper, the gelation behavior of egg yolk and its internal molecular agglomeration mechanism induced by heat, alkali, salt, freezing, high pressure, and salt-heating synergy were reviewed to provide a reference for further studies on the formation mechanisms and product development of egg yolk gel.

Effects of temperature on quality of preserved eggs during storage.

The effects of storage temperature (4°C, 25°C, and 35°C) on sensory quality, physicochemical properties, texture, molecular forces, flavor, and microbial indexes of preserved eggs were studied. The results showed that the sensory quality, weight loss rate, pH, and color of preserved eggs were significantly different at different storage temperatures (P < 0.05). Compared with high temperature and normal temperature storage, low temperature storage reduced weight loss rate by 55.15 and 64.1%, respectively, improved the sensory score (P < 0.05), inhibited the reduction of pH and the increase of total volatile base nitrogen (P < 0.05), and decreased the change of color (P < 0.05). During storage, there was no difference in the springiness of preserved egg white stored at different temperatures (P > 0.05). Hardness and chewiness at 3 different temperatures increased first and then decreased, and low temperature significantly inhibited the progress of these changes to a certain extent (P < 0.05). The content of ionic bond in egg white first decreased and then increased, and content of disulfide bond increased first and then decreased. Content of ionic bond in yolk decreased all the time, and high temperature could promote this change. Whatever the temperature was, the content of free amino acids in preserved egg white and yolk increased first and then decreased, and the total content of amino acids stored at different temperatures was significantly different (P < 0.05). The content of free fatty acids in yolk decreased. At the end of storage, no microorganisms were detected in 3 temperatures during the storage period of 84 D. The results showed that low temperature storage is more conducive for preservation of preserved eggs.

Isolation, purification, and structure identification of antioxidant peptides from embryonated eggs.

Antioxidant peptides are increasingly attracting researchers in medicine and foods. In the present study, egg white hydrolysates of embryonated eggs hatched on the sixth day (EWHD) were segmented consecutively by ultrafiltration membranes with small tangential flow ultrafiltration system. Four segments with more than 30, 30 to 10 kDa, 10 to 5 kDa, and less than 5 kDa of molecular weight cut-off (MWCO) values were separated and were labeled as MWCOI, MWCOII, MWCOIII, and MWCOIV, respectively. The antioxidant activities of segments were investigated by performing DPPH•, •OH radical scavenging, ultra oxygen anion (O2-•), total antioxidant capacity, and reducing power experiments. The results indicated that MWCOI has the strongest scavenging activities on DPPH• radical. However, MWCOIV has the strongest scavenging activities on •OH, O2-•, total antioxidant capacity, and reducing power, which revealed that MWCOIV has strong antioxidant activity. MWCOIV was further separated into 14 fractions via semipreparative reverse-phased high-performance liquid chromatography (RP-HPLC), and their antioxidant activity was evaluated by different antioxidant assays in vitro. The fractions 10 and 7 had strong antioxidant activities. The purities of these 2 fractions were determined by analytical RP-HPLC. Moreover, both fractions 10 and 7 displayed high purity levels, and they were identified by quadrupole time-of-flight tandem mass spectrometry. Only fraction 10, with a molecular weight of 204 Da, can be identified to be Ser-Val. EWHD can be considered as a promising source of natural food antioxidants for the development of functional food.

Deciphering the groove binding modes of tau-fluvalinate and flumethrin with calf thymus DNA.

Tau-fluvalinate (TFL) and flumethrin (FL), widely used in agriculture and a class of synthetic pyrethroid pesticides with a similar structure, may cause a potential security risk. Herein, the modes of binding in vitro of TFL and FL with calf thymus DNA (ctDNA) were characterized by fluorescence, UV-vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy with the aid of viscosity measurements, melting analyses and molecular docking studies. The fluorescence titration indicated that both TFL and FL bound to ctDNA forming complexes through hydrogen bonding and van der Waals forces. The binding constants of TFL and FL with ctDNA were in the range of 10(4)Lmol(-1), and FL exhibited a higher binding propensity than TFL. The iodide quenching effect, single/double-stranded DNA effects, and ctDNA melting and viscosity measurements demonstrated that the binding of both TFL and FL to ctDNA was groove mode. The FT-IR analyses suggested the A-T region of the minor groove of ctDNA as the preferential binding for TFL and FL, which was confirmed by the displacement assays with Hoechst 33258 probe, and the molecular docking visualized the specific binding. The changes in CD spectra indicated that both FL and TFL induced the perturbation on the base stacking and helicity of B-DNA, but the disturbance caused by FL was more obvious. Gel electrophoresis analyses indicated that both TFL and FL did not cause significant DNA cleavage. This study provides novel insights into the binding properties of TFL/FL with ctDNA and its toxic mechanisms.

Intercalation binding of food antioxidant butylated hydroxyanisole to calf thymus DNA.

The binding properties of food antioxidant butylated hydroxyanisole (BHA) associated with calf thymus DNA (ctDNA) in physiological buffer (pH 7.4) were investigated. Experimental results based on fluorescence, UV-vis absorption, circular dichroism (CD), viscosity measurements and autodocking techniques confirmed the intercalation binding between BHA and ctDNA. The changes in Fourier transform infrared spectra of ctDNA induced by BHA suggested that BHA was more prone to bind to G-C rich region of ctDNA, which was further ascertained with the molecular docking studies. Analysis of the CD spectra indicated that this binding interaction led to a transformation from B-like DNA structure toward A-like conformation. The complexation of BHA with ctDNA was driven mainly by hydrogen bonds and hydrophobic forces. The binding constants of the BHA-ctDNA complex were calculated to be 2.03 × 10(4), 1.92 × 10(4) and 1.59 × 10(4)L mol(-1) at 298, 304 and 310 K, respectively. Gel electrophoresis results suggested that intercalated BHA molecules did not significantly affect plasmid DNA. Moreover, the concentration profiles and the spectra for the three reaction components (BHA, ctDNA, and BHA-ctDNA complex) of the system by resolving the augmented UV-vis spectral data matrix with the use of multivariate curve resolution-alternating least squares approach provided quantitative data to estimate the progress of BHA-ctDNA interaction. This study is expected to provide new insights into the mechanism of interaction between BHA and ctDNA.

[Optimization of ultrasound-assisted extraction combined with AFS by response surface methodology for rapid determination of trace mercury in tea leaves].

A rapid ultrasound-assisted extraction (UAE) procedure was developed for the determination of trace mercury (Hg) in tea leaves combined with atomic fluorescence spectrometry. Three variables including sonication time (St), ultrasonic bath temperature (T) and HNO3 : H2O2 (1 : 1, phi) volume (A2) showed the significant effect on extraction rate of total Hg evaluated by a Plackett-Burman design, and they were further optimized by a central composite design and response surface methodology. The results showed that the optimum extraction conditions were as follows: presonication time 6 min, St 8. 1 min, T 70. 5 degreesC, A2 4. 4 mL, and sample mass 300 mg. GBW10016 (tea leaves) was used as certified reference material; for comparative purposes, a microwave-assisted digestion (MAD) was used. The result obtained by optimized UAE method showed good agreement with the certified values. Under optimal conditions, recovery was evaluated to be 94.2% - 102.0% and the limit of detection 0.007 8 microg x L(-1). The relative standard deviation (RSD) of replicate measurements was generally less than 10%. The proposed UAE method was successfully applied to the determination of Hg in 63 samples of fresh tea leaves and 10 different branded tea samples. No significant differences were established between the analytical results of UAE method and MAD method. The Hg concentrations of them were found in the range of 4.6-17.3 microg x kg(-1) on a dried basis, which were within the permissible limit of the NY659-2003.