Effects of Exogenous Enzymatic Treatment During Processing on the Sensory Quality of Summer Tieguanyin Oolong Tea from the Chinese Anxi County.

In order to attenuate the bitter taste and improve the aroma of the summer tieguanyin oolong tea from the Chinese Anxi county, the effects of processing treatment with exogenous laccase and α-galactosidase on tea sensory quality and related compounds were investigated. The solutions of laccase and/or α-galactosidase were sprayed on the tea leaves before the first drying process. The sensory evaluation results showed that the sensory quality of the tea was significantly enhanced with the enzymatic treatment. The combined application of laccase at 8.25 and α-galactosidase at 22 U per kg of fresh tea shoots achieved the most satisfying sensory quality. Further analysis of flavour-related constituents was carried out by HPLC and GC-MS. The HPLC analysis showed that the contents of catechins and total polyphenols were reduced, compared to the untreated group, by 11.9 and 13.3% respectively, and the total soluble sugars and water extract content were increased by 19.4 and 6.6% respectively, after the treatment with both enzymes. The decrease of catechins and total polyphenols reduced the bitterness and astringency of the summer tea, while the increase of total soluble sugars and water extract content improved the sweetness and mellow taste. The aromatic compound data from GC-MS showed that the total essential oil content in these tea samples co-treated with laccase and α-galactosidase increased significantly, in which aldehydes, alcohols, esters and alkenes increased by 23.28, 37.05, 20.10 and 38.99%, respectively. Our data suggest that the exogenous enzymatic treatment can enhance the summer oolong tea quality, especially its taste and aroma.

Compatibility studies on tea polysaccharide/amylose/water and tea polysaccharide/amylopectin/water.

The compatibilities of amylose/tea polysaccharide (Am/TPS) and amylopectin/tea polysaccharide (Ap/TPS) in water were investigated with theoretical calculations and experimental measurements. To achieve this, dilute-solution viscometry (DSV) and high-speed differential scanning calorimetry (hyper-DSC) were used. The compatibility criteria on the basis of Δb(m), ΔB(m), µ, Δ[η](m) and thermodynamic parameters, T(g) and ΔT(g) were estimated. The data obtained from DSV show that the Am/TPS mixtures with 0.65:0.35, the Ap/TPS mixtures with (a) 0.85:0.15 and (b) 0.75:0.25 at limited moisture are completely miscible. The results were also confirmed using DSC. A texture analyzer was also used to study effects of Am/TPS and Ap/TPS with different weight fractions on the textures of mixed sol. The results show that the firmness, consistency, cohesiveness and index of viscosity of the Am/TPS and Ap/TPS sol increase with the increase of TPS level and that TPS could provide a more desirable physical structure for starch-based foods.

Antiseptic activity and phenolic constituents of the aerial parts of Vitex negundo var. cannabifolia.

Four phenolics, salviaplebeiaside (1), γ-tocopherol (2), chrysosplenol-D (4), and isovitexin (5), along with α-tocoquinone (3) and ß-sitosterol (6) were isolated from the aerial parts of Vitex negundo var. cannabifolia. The isolation was performed using bio-assay tracking experiments. The structures of compounds 1-5 were established by spectroscopic means. The antibacterial activities of the compounds were assessed against Escherichia coli, Bacillus subtilis, Micrococcus tetragenus and Pseudomonas fluorescens. Chrysosplenol-D (4) exhibited activities against all the four spoilage microorganisms.