Zaixiang Lou

Antibacterial Activity and Mechanism of Action of Chlorogenic Acid

In this study, the antibacterial activity and mechanism of action of chlorogenic acid against bacteria were assessed. The data from minimum inhibitory concentration (MIC) values showed that chlorogenic acid effectively inhibited the growth of all tested bacterial pathogens, and the MIC values were ranging from 20 to 80 μg/mL. An investigation into action mode of chlorogenic acid against the pathogen indicated that chlorogenic acid significantly increased the outer and plasma membrane permeability, resulting in the loss of the barrier function, even inducing slight leakage of nucleotide. The leakage of cytoplasmic contents was also observed by electron micrographs. These results supported our hypothesis that chlorogenic acid bound to the outer membrane, disrupted the membrane, exhausted the intracellular potential, and released cytoplasm macromolecules, which led to cell death.

Improved extraction and identification by ultra performance liquid chromatography tandem mass spectrometry of phenolic compounds in burdock leaves

The simultaneous ultrasonic and microwave assisted extraction (UMAE) technique was first employed to obtain phenolics. The effects of UMAE variables including extraction time, microwave power, and solvent to solid radio on the yield of phenolics were investigated. The optimized conditions were as follows: solvent to solid ratio was 20:1 (ml/g), extraction time was 30s, microwave power was 500W and two times of extraction. Moreover, the phenolic yield of UMAE was higher than that by maceration, indicating a significant reduction of extraction time and an improvement of efficiency. The phenomenon is related to the strong disruption of leaf tissue structure by microwave induced expansion and ultrasonic shaking, which had been observed with the scanning electron microscopy. The phenolic compositions of the extract was then identified by ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), 10 compounds had been characterized, providing a more complete identification of phenolic compounds in burdock leaves than previously reported. The occurrence of benzoic acid and p-coumaric acid is reported for the first time. This study suggests that UMAE is a good alternative for the extraction of phenolics, with a great potential for industrial application. Also, UMAE provides a new sample preparation technique for characterization of the phenolic compounds from plants.

Ionic liquids based simultaneous ultrasonic and microwave assisted extraction of phenolic compounds from burdock leaves

The ionic liquids based simultaneous ultrasonic and microwave assisted extraction (IL-UMAE) technique was first proposed and applied to isolate compounds. The ionic liquids comprising a range of four anions, five 1-alkyl-3-methylimidazolium derivatives were designed and prepared. The results suggested that varying the anion and cation both had apparent effects on the extraction of phenolics. The results also showed that irradiation power, time and solid-liquid ratio significantly affected the yields. The yields of caffeic acid and quercetin obtained by IL-UMAE were higher than those by regular UMAE. Compared with conventional heat-reflux extraction (HRE), the proposed approach exhibited higher efficiency (8-17% enhanced) and shorter extraction time (from 5h to 30s). The results indicated ILUMAE to be a fast and efficient extraction technique. Moreover, the proposed method was validated by the reproducibility and recovery experiments. The ILUMAE method provided good recoveries (from 96.1% to 105.3%) with RSD lower than 5.2%, which indicated that the proposed method was credible. Based on the designable nature of ionic liquids, and the rapid and highly efficient performance of the proposed approach, ILUMAE provided a new alternative for preparation of various useful substances from solid samples.

Removal of caffeine from green tea by microwave-enhanced vacuum ice water extraction.

In order to selectively remove caffeine from green tea, a microwave-enhanced vacuum ice water extraction (MVIE) method was proposed. The effects of MVIE variables including extraction time, microwave power, and solvent to solid radio on the removal yield of caffeine and the loss of total phenolics (TP) from green tea were investigated. The optimized conditions were as follows: solvent (mL) to solid (g) ratio was 10:1, microwave extraction time was 6 min, microwave power was 350 W and 2.5 h of vacuum ice water extraction. The removal yield of caffeine by MVIE was 87.6%, which was significantly higher than that by hot water extraction, indicating a significant improvement of removal efficiency. Moreover, the loss of TP of green tea in the proposed method was much lower than that in the hot water extraction. After decaffeination by MVIE, the removal yield of TP tea was 36.2%, and the content of TP in green tea was still higher than 170 mg g(-1). Therefore, the proposed microwave-enhanced vacuum ice water extraction was selective, more efficient for the removal of caffeine. The main phenolic compounds of green tea were also determined, and the results indicated that the contents of several catechins were almost not changed in MVIE. This study suggests that MVIE is a new and good alternative for the removal of caffeine from green tea, with a great potential for industrial application.

Antioxidant activity and chemical composition of the fractions from burdock leaves.

The antioxidant activities of each burdock leaves fraction were first investigated alone and in combination with tertiary butylhydroquinone (TBHQ). The burdock leaves extract was fractioned with petroleum ether, ethyl acetate, n-butanol, and water, named as PF, EF, BF, and WF, respectively. The EF exhibited the highest antioxidant activity. Although TBHQ exhibited higher lipid peroxidation inhibitory activity than EF, the reducing power, superoxide anion scavenging capability, DPPH radical and hydroxyl radicals scavenging ability of EF were higher than those of synthetic antioxidant (TBHQ). Moreover, a synergistic antioxidant effect between EF and TBHQ was first demonstrated by isobolographic analysis, indicating that EF dramatically enhances the antioxidant efficiency of TBHQ. For all the fractions, the antioxidant capacity had a significant correlation with total phenolic content. The phenolic compounds of the fractions were then identified, namely chlorogenic acid, o-hydrobenzoic acid, caffeic acid, p-coumaric acid, and rutin. The results indicate that the EF could be used as sources of nature antioxidant in food industry, and allows a decrease of about 4 folds in the amounts of the synthetic compounds used.

Ionic liquid-based ultrasonic/microwave-assisted extraction combined with UPLC–MS–MS for the determination of tannins in Galla chinensis

Ionic liquid was used as extraction solvents and applied to the extraction of tannins from Galla chinensis in the simultaneous ultrasonic- and microwave-assisted extraction (UMAE) technique. Several parameters of UMAE were optimised, and the results were compared with of the conventional extraction techniques. Under optimal conditions, the content of tannins was 630.2 ± 12.1 mg g−1. Compared with the conventional heat-reflux extraction, maceration extraction, regular ultrasound- and microwave-assisted extraction, the proposed approach exhibited higher efficiency (11.7–22.0% enhanced) and shorter extraction time (from 6 h to 1 min). The tannins were then identified by ultraperformance liquid chromatography tandem mass spectrometry. This study suggests that ionic liquid-based UMAE is an efficient, rapid, simple and green sample preparation technique.

Purification and characterization of d-Gal-6-sulfurylase from Eucheuma striatum

D-Gal-6-sulfurylase catalyzing the conversion of μ-carrageenan into κ-carrageenan was extracted from Eucheuma striatum and purified by ammonium sulfate precipitation, hydrophobic interaction chromatography and ion exchange chromatography. The purified enzyme was a monomeric protein with a molecular mass of about 65 kDa as shown in SDS-PAGE. The maximum activity of the enzyme was observed at pH 7.0 and temperature 40°C. Km value for μ-carrageenan was 4.31 mM, and the corresponding Vmax was 0.17 mM min(-1). The carrageenan treated with 10 U of the purified enzyme exhibited 7.1-fold increase in gel strength with a removal of 30% sulfate groups. (1)H NMR spectral analysis of the control and enzyme treated carrageenan confirmed the conversion of μ- into κ-carrageenan and highlighted the specificity of Gal-6-sulfurylase for μ-carrageenan. This Gal-6-sulfurylase provides an eco-friendly and alternative for alkali treatment method to produce high gel strength κ-carrageenan.

Metabolomics-Based Screening of Biofilm-Inhibitory Compounds against Pseudomonas aeruginosa from Burdock Leaf

Screening of anti-biofilm compounds from the burdock leaf based on metabolomics is reported here. The crystal violet assay indicated 34% ethanol elution fraction of burdock leaf could completely inhibit biofilm formation of Pseudomonas aeruginosa at 1 mg·mL−1. Then, the chemical composition of burdock leaf fraction was analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) and 11 active compounds (chlorogenic acid, caffeic acid, p-coumaric acid, quercetin, ursolic acid, rutin, cynarin, luteolin, crocin, benzoic acid, and Tenacissoside I) were identified. Lastly, UPLC-MS analysis was employed to obtain the metabolic fingerprints of burdock leaf fractions before and after inhibiting the biofilm of Pseudomonas aeruginosa. The metabolic fingerprints were transformed to data, analyzed with PLS-DA (partial least squares discriminant analysis) and the peaks whose area was significantly changed were found out. Thus, 81 compounds were screened as potential anti-biofilm ingredients. Among them, rutin, ursolic acid, caffeic acid, p-coumaric acid and quercetin were identified and confirmed as the main anti-biofilm compounds in burdock leaf. The study provided basic anti-biofilm profile data for the compounds in burdock leaf, as well as provided a convenient method for fast screening of anti-biofilm compounds from natural plants.

Star anise (Illicium verum Hook. f.) as quorum sensing and biofilm formation inhibitor on foodborne bacteria: study in milk

Bacteria use quorum sensing (QS) systems to communicate with each other and regulate microbial group behavior, such as the secretion of virulence factors, including biofilm formation. In order to explore safe, edible agents, the potential of star anise (SA) as an anti-QS and antibiofilm agent and its possible application in milk safety were investigated. Staphylococcus aureus , Salmonella Typhimurium, Pseudomonas aeruginosa , and biosensor strain Chromobacterium violaceum were selected as test strains for QS, biofilm, and exopolysaccharide assays. The percent acidities and total plate counts were determined to evaluate the quality of biofilm-inoculated and noninoculated milk. The yield of SA extraction was 25.90% ± 0.2% (w/w). At sub-MIC, SA extract did not show any effect on bacterial growth. The production of violacein was inhibited by 89% by SA extract. The extract also inhibited the formation of biofilm by up to 87% in a dose-dependent manner. Inhibition rates of 70.45%, 42.82%, and 35.66% were found for exopolysaccharide production. The swarming motility of S. aureus was reduced by about 95.9% by SA extract. Confocal laser scanning microscopy analysis confirmed that the development of biofilm architecture was hampered. It was found that SA extract could delay the spoilage of milk. In the endeavor to avoid drug resistance, pathogenesis, and resistance to biocides while improving food safety and avoiding health hazard issues arising from synthetic chemicals, SA extract could be used as a potential QS and biofilm inhibitor.

Determination of preservative residues and microbial contents of commercial Chinese duck neck meat

ABSTRACT Duck neck meat products are traditional, popular snack items in China for its attractive spicy taste, flavor and texture. These products are perishable and different types of chemical preservatives are used extensively. This study determined the levels of preservatives and microbial load in Chinese duck neck meat product by gas chromatography and agar plate methods, respectively. The results showed that Chinese duck neck meat product contains methyl-p-hydroxybenzoate (E-218) in the range 21.15 μg/g–14.5 mg/g, propionic acid (E-280) in the range 26.84–30.24 mg/g and benzoic acid (E-210) in the range not detected – 15.99 μg/g. Sorbic acid (E-200) was not detected. The total plate counts were 1.01–2.03 log cfu/g, and Lactobacilli counts were 1.04–1.43 log cfu/g. Refrigerated raw duck neck contained all the tested microorganisms while yeast, mold and salmonella were not detected in all of the processed duck neck meat products.