Xiaoyun Xu

A structure–activity relationship study of flavonoids as inhibitors of E. coli by membrane interaction effect

Flavonoids exhibit a broad range of biological activities including antibacterial activity. However, the mechanism of their antibacterial activity has not been fully investigated. The antibacterial activity and membrane interaction of 11 flavonoids (including 2 polymethoxyflavones and 4 isoflavonoids) against Escherichia coli were examined in this study. The antibacterial capacity was determined as flavonoids>polymethoxyflavones>isoflavonoids. Using fluorescence, it was observed that the 5 flavonoids rigidified the liposomal membrane, while the polymethoxyflavones and isoflavonoids increased membrane fluidity. There was a significant positive correlation between antibacterial capacity and membrane rigidification effect of the flavonoids. A quantitative structure-activity relationship (QSAR) study demonstrated that the activity of the flavonoid compounds can be related to molecular hydrophobicity (CLogP) and charges on C atom at position3 (C3). The QSAR model could be used to predict the antibacterial activity of flavonoids which could lead to natural compounds having important use in food and medical industry.

Acid-induced gelation behavior of soybean protein isolate with high intensity ultrasonic pre-treatments.

High intensity ultrasonic (HUS, 20 kHz, 400 W) pre-treatments of soybean protein isolate (SPI) improved the water holding capacity (WHC), gel strength and gel firmness (final elastic moduli) of glucono-δ-lactone induced SPI gels (GISG). Sonication time (0, 5, 20, and 40 min) had a significant effect on the above three properties. 20 min HUS-GISG had the highest WHC (95.53 ± 0.25%), gel strength (60.90 ± 2.87 g) and gel firmness (96340Pa), compared with other samples. Moreover, SH groups and non-covalent interactions of GISG also changed after HUS pre-treatments. The HUS GISG had denser and more uniform microstructures than the untreated GISG. Rheological investments showed that the cooling step (reduce the temperature from 95 to 25 °C at a speed of 2 °C/min) was more important for the HUS GISG network formation while the heat preservation step (keep temperature at 95 for 20 min) was more important for the untreated GISG. HUS reduced the particle size of SPI and Pearson correlation test showed that the particle size of SPI dispersions was negatively correlated with WHC, gel strength and gel firmness.

Effect of Se treatment on glucosinolate metabolism and health-promoting compounds in the broccoli sprouts of three cultivars.

Broccoli sprouts are natural functional foods for cancer prevention because of their high glucosinolate (GSL) content and high selenium (Se) accumulation capacity. The regulation mechanism of Se on GSL metabolism in broccoli sprouts was explored. In particular, the effects of Se treatment (100 μmol/L selenite and selenate) on the Se, sulfur (S), glucosinolate and sulforaphane contents; myrosinase activity and health-promoting compounds (ascorbic acid, anthocyanin, total phenolics and flavonoids) of three, 5 day old, cultivars were investigated. The treatment did not influence the total GSL and ascorbic acid contents; significantly increased the myrosinase activity and sulforaphane, anthocyanin and flavonoids contents; and decreased the total phenolics content. The increase in sulforaphane during early growth can be primarily attributed to the increased myrosinase activity caused by Se treatment. Broccoli sprouts with suitable selenite and selenate concentrations, in the early growth days, could be desirable for improved human health.

3D-QSAR and docking studies of flavonoids as potent Escherichia coli inhibitors.

Flavonoids are potential antibacterial agents. However, key substituents and mechanism for their antibacterial activity have not been fully investigated. The quantitative structure-activity relationship (QSAR) and molecular docking of flavonoids relating to potent anti-Escherichia coli agents were investigated. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were developed by using the pIC50 values of flavonoids. The cross-validated coefficient (q2) values for CoMFA (0.743) and for CoMSIA (0.708) were achieved, illustrating high predictive capabilities. Selected descriptors for the CoMFA model were ClogP (logarithm of the octanol/water partition coefficient), steric and electrostatic fields, while, ClogP, electrostatic and hydrogen bond donor fields were used for the CoMSIA model. Molecular docking results confirmed that half of the tested flavonoids inhibited DNA gyrase B (GyrB) by interacting with adenosine-triphosphate (ATP) pocket in a same orientation. Polymethoxyl flavones, flavonoid glycosides, isoflavonoids changed their orientation, resulting in a decrease of inhibitory activity. Moreover, docking results showed that 3-hydroxyl, 5-hydroxyl, 7-hydroxyl and 4-carbonyl groups were found to be crucial active substituents of flavonoids by interacting with key residues of GyrB, which were in agreement with the QSAR study results. These results provide valuable information for structure requirements of flavonoids as antibacterial agents.

Adsorption–desorption properties and characterization of crosslinked Konjac glucomannan-graft-polyacrylamide-co-sodium xanthate

A new flocculant, based on Konjac-graft-poly (acrylamide)-co-sodium xanthate (CKAX), was synthesized in aqueous solution using epichlorohydrin (ECH) as the cross-linker and ceric ammonium nitrate (CAN) as the initiator. X-ray diffraction indicated the existence of strong interaction between KGM and reactant, including intermolecular and intramolecular hydrogen bonds. Microscopy images exhibited the appropriate pore size and distribution, which might be related to a higher capacity of flocculation and adsorption. Thermo gravimetric analysis showed that the synthetic polymer could improve the thermo-stability of the natural polysaccharides, and there was a positive correlation between polymer residual weight and flocculation. The adsorption and desorption properties for copper ions indicated that the adsorption rate could be described by a pseudo-second-order rate model, and the Freundlich model provides the best fit for the resulting adsorption isotherm. The flocculant can be regenerated in HNO(3) solution.

Effects of lard on the formation of volatiles from the Maillard reaction of cysteine with xylose.

BACKGROUND The presence of lipid oxidation products in the Maillard reaction pathway is of particular interest today. The objective of this study was to investigate the effect of lard and its oxidation products on the formation of volatiles from cysteine and xylose model systems. RESULTS Headspace volatiles generated in reaction mixtures were examined by solid-phase microextraction in combination with gas chromatography-mass spectrometry. The addition of lipid had a suppressing effect on most of the sulfur-containing compounds derived from the reaction between cysteine and xylose, especially for 2-methyl-3-furanthiol, 2-furanmethanethiol, 2-methylthiophene, and 3-methylthiophene. One of the intermediates-furfural-was also formed in much lower concentration when lard was present. In addition, cysteine and xylose modified lipid oxidation pathways, so that lipid-derived alcohols, alkylfurans and aliphatic acids were formed rather than aldehydes. Compared with the lard heated alone, most aldehydes were formed at lower levels in the lard-containing reaction mixtures, and several aldehydes including hexanal, heptanal, (2E)-heptenal and (2E,4E)-heptadienal were absent. CONCLUSION The addition of lipid was inhibitory to the formation of most sulfur-containing compounds in the Maillard reaction. Furthermore, Maillard reaction products influenced the formation of products from lipid oxidation.

Brettanomyces as a Starter Culture in Rice-Steamed Sponge Cake: A Traditional Fermented Food in China

The potential use of Brettanomyces anomalus PSY-001 as an additional starter culture for the production of Rice-steamed sponge cake (RSSC), a traditional fermented food in China, was investigated. Two productions of RSSC, each containing batches of experimental cakes with Brettanomyces added and reference cakes with the leavened liquid added were carried out. For both experimental and reference cakes, chemical analysis and sensory evaluation were carried out during the fermentation period. The results showed that experimental cakes had desirable aroma and taste. The observed differences indicate a positive contribution to the overall quality of RSSC by B. anomalus PSY-001.

Untargeted metabolomics reveals predominant alterations in primary metabolites of broccoli sprouts in response to pre-harvest selenium treatment

Broccoli sprouts have attracted considerable attention because of their abundant phytochemicals and high selenium accumulation capacity, which reportedly reduce the risks of different cancers and cardiovascular diseases. In this study, an untargeted metabolomics approach was developed to investigate the effect of 5 days of treatment with 100 μmol/L selenate on the metabolome of broccoli sprouts. Results showed that the total sulfur content was slightly lower and the total selenium content was significantly higher in the selenate-treated sprouts. The multivariate statistical analyses showed that serine, d-erythronolactone, melezitose and tyrosine were obviously up-regulated, but d-glyceric acid, succinic acid and citric acid were down-regulated after selenate treatment. Moreover, metabolite pathway analyses were used to support the identification of subtle but significant changes among groups of related metabolites that cannot be observed with conventional approaches. Selenate treatment influenced the metabolism of β-alanine and glutathione, as well as the biosynthesis of plant metabolite related to the precursors of glucosinolate. These results could explain why the total glucosinolate decreased after selenate treatment.

Rheological, sensory, and microstructural properties of fresh and frozen/thawed mashed potatoes enriched with different proteins

ABSTRACT In this study, the effect of the addition of soybean protein isolate (SPI), whey protein isolate (WPI), whole milk powder (WMP), and sodium caseinate (SC) on the rheological, physical, sensory, and structural properties of fresh and frozen/thawed mashed potatoes formulated with added cryoprotectants [kappa-carrageenan (κ-C) and xanthan gum (XG)] was compared. Steady shear flow rate curves indicated a non-Newtonian fluid and exhibited typical shear thinning (pseudoplastic) behavior (n < 1) with all added proteins. The results showed that there is no significant change in the apparent viscosity (ηapp) of fresh mashed potatoes (FMP) and frozen/thawed mashed potatoes (F/TMP) with added WMP and SC at a concentration of 5 g/kg. While the addition of SPI at a concentration of 10 g/kg increased the ηapp and pseudoplasticity, which indicates that the SPI behaves as harder fillers. Based on the sensory evaluation results, WPI and WMP could incorporate to FMP without losing the sensory quality of the product. F/TMP samples with addition of SPI were judged more acceptable than other processed samples, evidencing the ability of this protein to reduce the influence of freeze/thaw process.