Analysis of the aroma change of instant green tea induced by the treatment with enzymes from Aspergillus niger prepared by using tea stalk and potato dextrose medium

The mining of thermostable β-glucosidase for tea aroma enhancement under brewing conditions

The β-glucosidases known to improve tea aroma are all mesothermal enzymes, limiting their use under brewing conditions. Based on the properties analysis and molecular docking, the thermostable β-glucosidase (TPG) from Thermotoga petrophlia showed potential to enhance tea aroma. Treatment by recombinant TPG at 90 °C, the floral, sweet and grassy notes of instant Oolong tea were increased, while the roasted, caramel and woody notes were decreased. The improved floral, sweet and grassy notes were related to increase releasing of benzyl alcohol (floral), geraniol (floral), (Z)-3-hexen-1-ol (grassy), benzaldehyde (sweet) and 1-hexanol (grassy) by TPG hydrolyzing of (Z)-3-hexenyl-β-D-glucopyranoside, hexanyl-β-D-glucopyranoside (HGP), benzyl-β-D-glucopyranoside, prunasin and geranyl-β-D-glucopyranoside (GGP), respectively. Although the catalytic efficiency of TGP to GGP was about twice that to HGP, HPG was more competitive than GGP when they mixed. Combined with microstructure analysis, the structure-function relationship of TPG-influencing tea aroma were understood. This study provided the method of how to mining new function of characterized β-glucosidases, as well as a theoretical basis for the development of new tea products.

Characterization of a novel multifunctional β-glucosidase/xylanase/feruloyl esterase and its effects on improving the quality of Longjing tea

Herein, a novel multifunctional enzyme β-glucosidase/xylanase/feruloyl esterase (GXF) was constructed by fusion of β-glucosidase and bifunctional xylanase/feruloyl esterase. The activities of β-glucosidase, xylanase, feruloyl esterase and acetyl xylan esterase displayed by GXF were 67.18 %, 49.54 %, 38.92 % and 23.54 %, respectively, higher than that of the corresponding single functional enzymes. Moreover, the GXF performed better in enhancing aroma and quality of Longjing tea than the single functional enzymes and their mixtures. After treatment with GXF, the grassy and floral odors of tea infusion were significantly improved. Moreover, GXF treatment could improve concentrations of flavonoid aglycones of myricetin, kaempferol and quercetin by 68.1-, 81.42- and 77.39-fold, respectively. In addition, GXF could accelerate the release of reducing sugars, ferulic acid and xylo-oligosaccharides by 9.48-, 8.25- and 4.11-fold, respectively. This multifunctional enzyme may have potential applications in other fields such as food production and biomass degradation.

Characterization of the Key Aroma Compounds in Different Aroma Types of Chinese Yellow Tea

Yellow tea is one of the six major tea categories in China. The floral fragrance type, high-fired fragrance type, fresh fragrance type, and corn-like fragrance type were the main aroma types of yellow tea screened by QDA. A total of 103 volatiles were identified in yellow teas by HS-SPME/GC-MS analysis. Using multivariate analysis and OAVs, forty-seven aroma compounds were identified as key aroma compounds for the formation of different aroma types of yellow teas. Among them, 8, 14, 7, and 18 key aroma compounds played an important role in the formation of aroma characteristics of floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. Furthermore, PLS analysis revealed that 12 aroma compounds were the key contributors to the 'floral and fruity' and 'sweet' attributes, five aroma compounds contributed to the 'roasted' attribute, and four aroma compounds related to the 'fresh' and 'grassy' attributes. This study provides new insights into the aroma characteristics formation of different aroma types of yellow teas and will provide a valuable theoretical basis for improving the flavor quality of yellow tea during the manufacturing process.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Evaluation of Volatile Profile and In Vitro Antioxidant Activity of Fermented Green Tea Infusion With Pleurotus sajor-caju (Oyster Mushroom)

Green tea has distinct astringency, bitter taste, and typical green flavor because of its post-harvest treatment without withering and enzymatic oxidation. Microbial fermentation has been identified as a promising strategy that could give green tea infusion a special taste flavor. This might be linked to the metabolic transformation ability of microorganisms. In this study, starter culture of edible mushroom Pleurotus sajor-caju (oyster mushroom) was used for submerged fermentation of green tea infusion in order to improve its flavor and taste quality. The volatile profile determined by headspace solid-phase microextraction, coupled with gas chromatography mass spectrometry, showed that the contents of (Z)-2-penten-1-ol and methyl heptadienone in green tea infusion were decreased significantly by the fermentation with the basidiomycete P. sajor-caju (p < 0.01), which would alleviate the herbal and grass flavor of green tea infusion to a certain extent. Meanwhile, the contents of linalool and geraniol were increased 9.3 and 11.3 times, respectively, whereas methyl salicylate was newly produced after fermentation by P. sajor-caju, endowing the fermented tea infusion with a pleasant flower and fruit aroma. In addition, the polyphenol profile was determined using high-performance liquid chromatography equipped with ion trap mass spectrometry, and the results indicated that the contents of most polyphenols in green tea infusion decreased significantly after fermentation by P. sajor-caju. The reduction of catechins and anthocyanins in fermented green tea infusion alleviated the astringency and bitterness. Moreover, the antioxidant activity of fermented green tea infusion was obviously decreased, especially the DPPH-free radical-scavenging ability and the ferric-reducing power. However, it is noteworthy that the ABTS-free radical scavenging ability was improved compared with the unfermented one, indicating that the increased tea pigments and volatile metabolites (such as linalool and geraniol) after fermentation with P. sajor-caju may also contribute to the antioxidant capacity of fermented green tea infusion. Overall, the innovative approach driven by P. sajor-caju fermentation has achieved promising potential to manipulate the green tea flavor.

Influence of Eurotium cristatum and Aspergillus niger individual and collaborative inoculation on volatile profile in liquid-state fermentation of instant dark teas

The three instant dark teas were produced from instant green tea (IGT) by liquid-state fermentations using the microorganisms Eurotium cristatum (EFT), Aspergillus niger (AFT), and sequential inoculation of E. cristatum/A. niger (EAFT), respectively. The volatile compounds of four tea samples were extracted by headspace-solid phase microextraction (HS-SPME) and analyzed using gas chromatography-mass spectrometry (GC-MS) coupled with chemometrics. A total of 97 volatile compounds were tentatively identified to distinguish three fermented instant dark from IGT. Alcohols, acids, esters, ketones, aldehydes, and heterocyclics could be clearly distinguished by principal component analysis (PCA), venn diagram, heatmap analysis and hierarchical cluster analysis (HCA). Descriptive sensory analysis revealed that AFT had a moldy, woody and herbal aroma; EFT showed woody and herbal aroma; and EAFT smelled an herbal, sweet, minty and floral aroma. This study indicates that fermentation using different microorganisms is critical in forming unique aroma characteristics of instant dark teas.

Insight into the volatile profiles of four types of dark teas obtained from the same dark raw tea material

Various dark teas are quite different in their volatile profiles, mainly due to the huge differences in the phytochemical profiles of dark raw tea and the diverse post-fermentation processing technologies. In this study, gas chromatography-mass spectrometry (GC-MS), qualitative GC-olfactometry (GC-O), and enantioselective GC-MS coupled with multivariate analysis were applied to characterise the volatile profiles of various dark teas obtained from the same dark raw tea material. A total of 159 volatile compounds were identified by stir bar sorptive extraction (SBSE) combined with GC-MS, and 49 odour-active compounds were identified. Moreover, microbial fermentation could greatly influence the distribution of volatile enantiomers in tea, and six pairs of enantiomers showed great diversity of enantiomeric ratios among various dark teas. These results suggest that post-fermentation processing technologies significantly affect the volatile profiles of various dark teas and provide a theoretical basis for the processing and quality control of dark tea products.