Huaiqiong Chen

Thymol Nanoencapsulated by Sodium Caseinate: Physical and Antilisterial Properties

In this work, thymol was encapsulated in sodium caseinate using high shear homogenization. The transparent dispersion at neutral pH was stable for 30 days at room temperature as determined by dynamic light scattering and atomic force microscopy, which agreed with high ζ potential of nanoparticles. The slightly decreased particle dimension during storage indicates the absence of Ostwald ripening. When molecular binding was studied by fluorescence spectroscopy, thymol was observed to bind with tyrosine and possibly other amino acid residues away from tryptophan of caseins. At pH 4.6 (isoelectric point of caseins), the stabilization of thymol nanoparticles against aggregation was enabled by soluble soybean polysaccharide, resulting from the combined electrostatic and steric repulsions. The encapsulated thymol showed the significantly improved antilisterial activity in milk with different fat levels when compared to thymol crystals, resulting from the quicker mixing and increased solubility in the milk serum. The transparent thymol nanodispersions have promising applications to improve microbiological safety and quality of foods.

Chemical Constituents of Agarwood Originating from the Endemic Genus Aquilaria Plants

by Huai-Qiong Chena), Jian-He Wei*a), Jun-Shan Yanga), Zheng Zhanga), Yun Yangb), Zhi-Hui Gaoa), Chun Suia), and Bao Gongb) a) Institute of Medicinal Plant Development (Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine, Ministry of Education), Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, P. R. China (phone: þ86-10-62818841; e-mail: wjianh@263.net) b) Hainan Branch Institute of Medicinal Plant (Hainan Provincial Key Laboratory of Resources Conservation and Development of Southern Medicine), Chinese Academy of Medical Sciences & Peking Union Medical College, Wanning 571533, P. R. China

Comparison of Compositions and Antimicrobial Activities of Essential Oils from Chemically Stimulated Agarwood, Wild Agarwood and Healthy Aquilaria sinensis (Lour.) Gilg Trees

The composition and antimicrobial activity of the essential oils which were obtained from agarwood originated from Aquilaria sinensis (Lour.) Gilg stimulated by the chemical method (S1) were characterized, taking wild agarwood (S2) and healthy trees (S3) respectively as the positive and negative controls. The chemical composition of S1 was investigated by gas chromatography-mass spectrometry (GC-MS). The essential oil of S1 showed a similar composition to that of S2, being rich in sesquiterpenes and aromatic constituents. However, the essential oil of S3 was abundant in fatty acids and alkanes. Essential oils of S1 and S2 had better inhibition activities towards Bacillus subtilis and Staphyloccus aureus, compared with essential oil of S3. Escherichia coli was not sensitive to any of them.

Whole-tree Agarwood-Inducing Technique: An Efficient Novel Technique for Producing High-Quality Agarwood in Cultivated Aquilaria sinensis Trees

Agarwood is the fragrant resin-infused wood derived from the wounded trees of Aquilaria species. It is a valuable non-timber forest product used in fragrances and as medicine. Reforestation for Aquilaria trees in combination with artificial agarwood-inducing methods serves as a way to supply agarwood and conserve of wild Aquilaria stock. However, the existing agarwood-inducing methods produce poor-quality agarwood at low yield. Our study evaluated a novel technique for producing agarwood in cultivated Aquilaria trees, called the whole-tree agarwood-inducing technique (Agar-Wit). Ten different agarwood inducers were used for comparison of Agar-Wit with three existing agarwood-inducing methods. For Aquilaria trees treated with these ten inducers, agarwood formed and spread throughout the entire tree from the transfusion point in the trunk to the roots and branches of the whole tree. Agarwood yield per tree reached 2,444.83 to 5,860.74 g, which is 4 to 28 times higher than that by the existing agarwood-inducing methods. Furthermore, this agarwood derived from Agar-Wit induction was found to have a higher quality compared with the existing methods, and similar to that of wild agarwood. This indicates Agar-Wit may have commercial potential. Induction of cultivated agarwood using this method could satisfy the significant demand for agarwood, while conserving and protecting the remaining wild Aquilaria trees.

Impacts of Sample Preparation Methods on Solubility and Antilisterial Characteristics of Essential Oil Components in Milk

ABSTRACT Essential oil components (EOCs) have limited water solubility and are used at much higher concentrations in complex food matrices than in growth media to inhibit pathogens. However, the correlation between solubility and activity has not been studied. The objective of this work was to characterize the solubility of EOCs in solvents and milk and correlate solubility with antilisterial activity. The solubilities of four EOCs, thymol, carvacrol, eugenol, and trans-cinnamaldehyde, in water was significantly increased in the presence of 5% (vol/vol) ethanol. In milk, the solubility of EOCs was lower than in water, with lower solubility in higher-fat milk. EOCs applied to milk as stock solutions (in 95% aqueous ethanol) enabled quicker dissolution and higher solubility in milk serum than other methods of mixing, such as end to end, and greater reductions of Listeria monocytogenes Scott A after 0 and 24 h. When the EOC concentration detected in milk serum was above the minimum bactericidal concentration, complete inhibition of L. monocytogenes in tryptic soy broth resulted. Therefore, the antilisterial properties in milk could be correlated with the solubility by comparison to the minimum inhibitory or bactericidal concentrations of EOCs. While the EOCs applied using ethanol generally had solubility and activity characteristics superior to those of other mixing methods, ethanol is not used to a great extent in nonfermented foods. Therefore, mixing methods without an organic solvent may be more readily adaptable to enhancing the distribution of EOCs in complex food systems.

Thermal and UV stability of β-carotene dissolved in peppermint oil microemulsified by sunflower lecithin and Tween 20 blend.

Microemulsions are suitable for simultaneous delivery of flavour oils and lipophilic bioactive compounds in transparent beverages. In the present study, the feasibility of delivering β-carotene in microemulsions formulated with peppermint oil and a blend of Tween® 20 and various amounts of sunflower lecithin was investigated. The poorly water- and oil-soluble β-carotene was dissolved in the transparent microemulsions that had particles smaller than 10nm and were stable during ambient storage for 65 d. The inclusion of β-carotene did not change the flow-behaviour and Newtonian viscosity. The degradation of β-carotene in microemulsions during ambient storage, ultraviolet radiation, and thermal treatments at 60 and 80 °C followed first order kinetics and was greatly suppressed when compared to the solution control. The antioxidant potential of peppermint oil and a greater content of lecithin in microemulsions enabled the better protection of β-carotene. The studied microemulsions may find various applications in manufacturing transparent beverages.

Microemulsions Based on a Sunflower Lecithin–Tween 20 Blend Have High Capacity for Dissolving Peppermint Oil and Stabilizing Coenzyme Q10

The objectives of the present study were to improve the capability of microemulsions to dissolve peppermint oil by blending sunflower lecithin with Tween 20 and to study the possibility of codelivering lipophilic bioactive compounds. The oil loading in microemulsions with 20% (w/w) Tween 20 increased from 3% (w/w) to 20% (w/w) upon gradual supplementation of 6% (w/w) lecithin. All microemulsions had particles of <12 nm that did not change over 70 d of storage at 21 °C. They had relatively low Newtonian viscosities and were physically and chemically stable after 50-200-fold dilution in water, resulting from similar hydrophile-lipophile-balance values of the surfactant mixture and peppermint oil. Furthermore, the microemulsions were capable of dissolving coenzyme Q10 and preventing its degradation at UV 302 nm, more significant for the microemulsion with lecithin. Therefore, natural surfactant lecithin can reduce the use of synthetic Tween 20 to dissolve peppermint oil and protect the degradation of dissolved lipophilic bioactive components in transparent products.

Development of genomic SSR and potential EST-SSR markers in Bupleurum chinense DC.

Nineteen genomic SSR markers were developed using inter-simple sequence repeat (ISSR)- suppression PCR technique in Bupleurum chinense DC., a widely used Chinese medicinal plant. A total of 126 alleles were detected across 22 individual plants of B. chinense DC. f. octoradiatum (Bunge) Shan et Sheh, with an average of 3 - 13 alleles per locus. The observed heterozygosity (HO) and the expected heterozygosity (HE) values ranged from 0.23 to 1.00 and from 0.29 to 0.92, respectively. Nine loci deviated from Hardy-Weinberg equilibrium (HWE) (P < 0.05) and eight pairs of loci showed significant linkage disequilibrium (LD) (Fisher’s exact test, P < 0.01). The species transferability of these genomic SSR markers was also detected in seven other Bupleurum species. Eight SSR markers were successfully amplified in all tested species. In addition, forty four EST-SSRs which can be amplified with expected sizes were identified from a B. chinense root cDNA library. The genomic SSR markers and potential EST-SSR markers developed in the present study should be useful for genetic diversity and molecular marker assistant selection breeding research in Bupleurum species.

Lactobionic acid enhances the synergistic effect of nisin and thymol against Listeria monocytogenes Scott A in tryptic soy broth and milk

Listeria monocytogenes is a Gram-positive opportunistic human pathogen and it remains a significant cause of foodborne illnesses. A variety of natural and synthetic compounds have been studied to inhibit the growth of L. monocytogenes in foods. Antimicrobial combinations with synergistic antilisterial properties can reduce the dose of each antimicrobial, which can be further enhanced by chelating compounds. Therefore, the objective of this study was to determine antilisterial properties of binary or ternary combinations of lactobionic acid (LBA), nisin, and thymol in tryptic soy broth (TSB), 2% reduced-fat milk, and whole milk. The results showed that the minimum inhibitory concentration (MIC) of nisin, thymol and LBA was 125IU/mL, 0.25mg/mL, and 10mg/mL, respectively. The ternary combination was the most effective in reducing MICs of antimicrobials, with the MIC of nisin, thymol, and LBA being 31.25IU/mL, 0.0625mg/mL, and 1.25mg/mL, respectively. In TSB with 0.6% yeast extract, L. monocytogenes grew in individual or binary antimicrobial treatments of 31.25IU/mL nisin, 0.0625mg/mL thymol, and 1.25mg/mL LBA within 24h at 32°C, while it was completely inhibited by the ternary combination. In 2% reduced-fat milk at 21°C, the ternary combination of nisin, thymol, and LBA at respective concentrations of 250IU/mL, 2mg/mL, and 10mg/mL completely inhibited the bacterium to below the detection limit in 72h while >2log (CFU/mL) bacteria was still detected in all the binary combinations after 120h. In whole milk, the combination of 500IU/mL nisin, 2mg/mL thymol, and 10mg/mL LBA reduced bacteria to around 2log (CFU/mL) in 4h at 21°C, and no bacterial recovery was observed after 5 d. This study suggested the potential of the ternary combination of nisin, thymol and LBA for food preservation.

Antimicrobial properties of nisin after glycation with lactose, maltodextrin and dextran and the thyme oil emulsions prepared thereof.

To clarify the reported conflicting antimicrobial activities of nisin after glycation, nisin was glycated with lactose, maltodextrin, and dextran at 70 °C and 50% relative humidity for 1-24 h. Nisin before and after glycation was studied for the first time to prepare thyme oil emulsions. The activity of glycated nisin and the thyme oil emulsions was tested in both tryptic soy broth (TSB) and 2% reduced fat milk. Results showed that nisin glycated with a smaller saccharide for a longer duration had a higher degree of glycation and the reduced number of positive charges lowered its antibacterial activity. The emulsified thyme oil had an additive effect with either glycated or native nisin against Listeria monocytogenes Scott A and Bacillus subtilis in TSB and 2% reduced fat milk. However, emulsions were less effective against L. monocytogenes Scott A in milk than same units of native nisin and same concentration of free thyme oil, likely due to the reduced availability of thymol and carvacrol, the main components of thyme oil. These results showed that glycation of nisin cannot broaden its antimicrobial activity and nisin is not a good compound to prepare emulsions of essential oils.