A Quantitative Analysis Model Established to Determine the Concentration of Each Source in Mixed Astaxanthin from Different Sources.

Astaxanthin from different sources possesses different biological activities and optical isomers. The ingredients of astaxanthin mixtures from different sources on the market have often been mislabeled. Therefore, it is important to determine the sources of astaxanthin and their respective concentrations in a mixture. To solve this problem, a quantitative analysis model was established and further verified. The results showed that the deviation between the calculated concentration and the actual concentration ranged from 0 to 7 µg/mL, and the recovery rate was between 88.90% and 103.56%. This indicates that the quantitative analysis model of astaxanthin was feasible and reliable. This study not only has important applications in the astaxanthin mixture component determination but may also shed light on the quantitative analysis of other sample mixtures with stereoisomers from different sources.

Characterization of the Aroma of an Instant White Tea Dried by Freeze Drying.

The aroma of an instant white tea (IWT) was extracted through simultaneous distillation-extraction (SDE) and analyzed by sensory evaluation, gas chromatography-mass spectrometry-olfactometry (GC-MS-O), aroma reconstruction, omission test and synergistic interaction analysis. Sensory evaluation showed the IWT was dominated with floral and sweet notes. The SDE extract had the aroma similar to the IWT. The main volatile components in the SDE extract were benzyl alcohol, linalool, hotrienol, geraniol, α-terpineol, coumarin, camphene, benzeneacetaldehyde, 2-hexanone, cis-jasmin lactone and phenylethyl alcohol. GC-MS-O and aroma reconstruction experiments showed 16 aroma-active compounds. Linalool, trans-ß-damascenone and camphene were the major contributors to floral, sweet and green notes based on flavor dilution analysis and omission test. Linalool and trans-ß-damascenone had synergistic effect to promote floral and sweet notes. Camphene and trans-ß-damascenone had synergistic effect to reduce green and sweet notes. The study helps to understand the aroma of IWT and antagonism interactions among aroma-active volatiles.

Enzymatic hydrolysis and auto-isomerization during ß-glucosidase treatment improve the aroma of instant white tea infusion.

The aroma changes in instant white tea resulting from ß-glucosidase treatment was investigated by quantitative descriptive analysis (QDA), gas chromatography-mass spectrometry (GC-MS), odour activity value analysis (OAV), aroma reconstruction and omission tests. The grassy, floral and sweet notes increased significantly (P < 0.05), and the roasted note decreased significantly (P < 0.05) upon ß-glucosidase treatment. Quantitative analysis showed that the concentrations of benzaldehyde, benzeneacetaldehyde, (Z)-3-hexen-1-ol, linalool, phenylethyl alcohol, cis-linalool oxide, trans-linalool oxide, hexanol, hotrienol and (E)-2-hexen-1-ol increased significantly (P < 0.05) after treatment; however, (Z)-3-hexen-1-ol isomerized to (E)-2-hexen-1-ol. OAV analysis, aroma reconstruction and the omission test showed that the grassy, floral and sweet notes increased as the (Z)-3-hexen-1-ol, cis/trans-linalool oxide and benzeneacetaldehyde increased, whereas the roasted note declined under the same conditions. The enzymatic hydrolysis of glycosidic precursors and the auto-isomerization of volatile compounds provide new information for understanding how ß-glucosidase treatment improves the aroma of tea products.

[Studies on the effects of steric hindrance of guest molecule on the formation of inclusion complexes by molecular luminescence].

Fluorescence and room temperature phosphoresce (CD-RTP) induced by cyclodextrin methods were employed to investigate the effects of steric hindrance of guest molecule on the formation of inclusion complexes of beta-cylcodextrin (beta-CD) and bromonaphthalene (BrN). It has been found that the RTP intensity of 2-BrN/beta-CD/n-Bu/ph was less than one third of that of 1-BrN/beta-CD/n-Bu/ph and fluorescence emission spectra of 2-BrN/beta-CD/n-Bu/ph had a red shift of 5-10 nm comparing with that of 1-BrN/beta-CD/n-Bu/ph under the optimum experimental conditions, respectively. These results exhibited that the steric locations of bromine in BrN strongly influenced the formation of inclusion complexes. The determination of the two quadri-inclusion complexes constants further demonstrated that the steric hindrance has a great effect on the formation of inclusion complexes. According to the above experimental results, the mechanism of formation of inclusion complexes were discussed briefly.

Growth-inhibitory and metal-binding proteins in Chlorella vulgaris exposed to cadmium or zinc.

Phytochelatins, with the general structure of (gamma-Glu-Cys)n-Gly (n=2-11), are usually recognized as being strongly induced by metals in microalgae and play an important role in the detoxification of heavy metals in environment. However, there have been few studies on metallothionein (MT) synthesis in Chlorella vulgaris (C. vulgaris) exposed to heavy metals. The present study describes the growth inhibition of C. vulgaris exposed to different concentrations of cadmium and zinc, and the induction of metal-binding MT-like proteins in the cells. The amounts of metal-binding proteins, induced in the alga exposed to different concentrations of Cd and Zn, were analyzed with a size-exclusion HPLC coupled to ICP-MS. After being purified with a gel filtration column (Sephadex G-75, 3.5cmx80cm) and a desalting column (G-25, 1.5cmx30cm), the isoforms and sub-isoforms of Zn-binding protein were characterized by a reverse phase-HPLC coupled to electrospray ionization and a triple quadrupole mass spectrometer (HPLC-ESI-MS/MS). In addition, the ultraviolet spectra of purified Zn-binding proteins were analyzed in media with different pH values. The results showed that the significant inhibitory effects (at p<0.05) on the cell growth were observed when excessive metals such as 80micromoll(-1) of Cd, and 60 and 80micromoll(-1) of Zn were added. The Cd/Zn-binding proteins induced in C. vulgaris exposed to Cd and Zn were referred to as Cd/Zn-MT-like proteins in which the mean molecular mass of the apo-MT-like was 6152Da. The induced Cd/Zn-MT-like proteins might be involved in the detoxification of heavy metals, such as cadmium and zinc, by the alga.