Effects of Fermentation with Eurotium cristatum on Sensory Properties and Flavor Compounds of Mulberry Leaf Tea.

Mulberry leaf tea (MT) is a popular Chinese food with nutrition and medicinal functions. Solid-state fermentation with Eurotium cristatum of MT (FMT) can improve their quality. Differences in chromaticity, taste properties, and flavor characteristics were analyzed to evaluate the improvements of the sensory quality of FMT. After fermentation, the color of the tea infusion changed. The E-tongue evaluation results showed a significant decrease in unpleasant taste properties such as sourness, bitterness, astringency, and aftertaste-bitterness, while umami and saltiness taste properties were enhanced post-fermentation. Aroma-active compounds in MT and FMT were identified and characterized. A total of 25 key aroma-active compounds were screened in MT, and 2-pentylfuran showed the highest relative odor activity value (ROAV). A total of 26 key aroma-active compounds were identified in FMT, and the newly formed compound 1-octen-3-one showed the highest ROAV, which contributed to FMT's unique mushroom, herbal, and earthy flavor attributes. 1-octen-3-one, (E)-2-nonenal, trimethyl-pyrazine, 2-pentylfuran, and heptanal were screened as the potential markers that contributed to flavor differences between MT and FMT. E. cristatum fermentation significantly altered the sensory properties and flavor compounds of MT. This study provides valuable insights into the sensory qualities of MT and FMT, offering a theoretical basis for the development of FMT products.

Characterization of the aroma-active compounds in Xiaokeng green tea by three pretreatment methods combined with gas chromatography-olfactometry (GC-O).

Chinese Xiaokeng green tea (XKGT) possesses elegant and fascinating aroma characteristics, but its key odorants are still unknown. In this study, 124 volatile compounds in the XKGT infusion were identified by headspace-solid phase microextraction (HS-SPME), stir bar sorptive extraction (SBSE), and solvent extraction-solid phase extraction (SE-SPE) combined with gas chromatography-mass spectrometry (GC-MS). Comparing these three pretreatments, we found HS-SPME was more efficient for headspace compounds while SE-SPE was more efficient for volatiles with higher boiling points. Furthermore, SBSE showed more sensitive to capture ketones then was effective to the application of pretreatment of aroma analysis in green tea. The aroma intensities (AIs) were further identified by gas chromatography-olfactometry (GC-O). According to the AI and relative odor activity value (rOAV), 27 compounds were identified as aroma-active compounds. Quantitative descriptive analysis (QDA) showed that the characteristic aroma attributes of XKGT were chestnut-like, corn-like, fresh, and so on. The results of network analysis showed that (E, Z)-2,6-nonadienal, nonanal, octanal and nerolidol were responsible for the fresh aroma. Similarly, dimethyl sulfide, (E, E)-2,4-heptadienal, (E)-2-octenal and ß-cyclocitral contributed to the corn-like aroma. Furthermore, indole was responsible for the chestnut-like and soybean-like aroma. This study contributes to a better understanding of the molecular mechanism of the aroma characteristics of XKGT.

Study on the dynamic change of volatile components of white tea in the pile-up processing based on sensory evaluation and ATD-GC-MS Technology.

The pile-up processing has a great impact on the flavor of white tea. To investigate the effects of the volatile accumulation of white tea with different piling thickness treatments, tea leaves from different thickness treatments were subjected to sensory quantitative description analysis and ATD-GC-MS detection in this study. As a result, 122 volatile components were identified from white tea with different treatments. A total of 8 key compounds, including isovaleraldehyde, isobutyraldehyde, 2-methyl-butanal, 1-octene-3-ol, linalool, pentanoic acid, hexanal and 1-hexanol were screened out using multivariate statistical analysis, which were characteristic components of grassy, floral-fruity, pekoe aroma and sweet flavors. The results of the selected key characteristic volatile compounds were consistent with the sensory quantitative description. The aroma of mid-pile dried tea (MD) was exhibited a harmonious and pleasant overall flavor. This study provides a novel insight into the accumulation of volatile during the withering step of white tea production.

The flavor substances changes in Fuliang green tea during storage monitoring by GC-MS and GC-IMS.

To study the effect of storage (for 0, 3, 6, and 12 months) on the flavor of green tea (GT), we monitored the volatile organic compounds (VOCs) in GT through gas chromatography (GC) combined with ion mobility spectrometry and headspace solid-phase micro extraction, GC-MS (mass spectrometry). Then, relative odor activity value (ROAV) was applied to analyze the aroma contribution of the VOCs. During storage, the polyphenol and caffeine contents gradually decreased from 22.38 % to 18.51 % and from 4.37 % to 3.74 %, respectively, and the total soluble sugar first increased and then decreased (from 4.89 % to 7.16 % and then 5.02 %). Although the total free amino acid contents showed a fluctuating trend, the content of cysteamine increased gradually. The contents of VOCs with positive contribution to GT aroma, including linalool, geraniol, nonanal, and 6-methyl-5-hepten-2-one, decreased. They also contributed less in the ROAV after storage. The ROAVs of nonanal, linalool, and geraniol decreased from 3.37 to 0.79, from 100 to 38.21, and from 2.98 to 1.8, respectively, after 12 months of storage. Principal component analysis can be used to identify the samples with different storage durations based on these data. Given the increase in amount of cysteamine and decrease in that of linalool oxide, oxidation may be not the only factor responsible for tea quality in storage.

Effects of lactic acid bacteria on antioxidant activity in vitro and aroma component of Eucommia ulmoides tea.

Eucommia ulmoides tea is a popular functional health drink in Asian countries, but its unique herbal aroma is difficult for consumers to accept. The effects of four lactic acid bacteria strains (Lactobacillus plantarium, Lactobacillus bulgaricus, Lactobacillus acidophilus and Streptococcus thermophilus) fermentation on the physicochemical property, antioxidant activity in vitro and aroma component of E. ulmoides leaves were studied. Within the four strains, the sample by L. bulgaricus fermentation showed the higher concentrations of chlorogenic acid, geniposidic acid and stronger antioxidant activity in vitro. Moreover, the sample by L. bulgaricus fermentation produced a stronger fruity and floral flavor. These results suggested that L. bulgaricus was the best strain for fermentation E. ulmoides tea. The differences between different strains should be considered when selecting lactic acid bacteria for raw material fermentation of fruits and vegetables.

Comparison on Changes of Volatile Components in Gecko Before and After Processing by HS-SPME-GC-MS / 中国实验方剂学杂志

ObjectiveOn the basis of sensory evaluation， the changes of volatile components in gecko before and after processing were compared， and the odor correction effect of different processing methods of gecko was discussed. MethodRaw products， fried yellow products， vinegar processed products， wine processed products， talcum powder scalding products and white wine sprayed products after scalding talcum powder of gecko were prepared， and 10 odor assessors were invited to evaluate the 6 samples in turn by sensory evaluation. Headspace solid-phase microextraction-gas chromatography-mass spectrometry （HS-SPME-GC-MS） and relative odor activity value （ROAV） were used to analyze the key odor components， and multivariate statistical methods were used to analyze the difference of volatile components between raw and processed products of gecko. Taking water-soluble extract and protein contents as internal indicators， sensory evaluation score and content ranking of differential components as external indicators， and assigning a weight of 0.25 to them respectively， the comprehensive scores of raw products and processed products of gecko were calculated to evaluate the odor correction effect of each processing method. ResultThe average sensory evaluation scores of the raw products， fried yellow products， vinegar processed products， wine processed products， talcum powder scalding products and white wine sprayed products after scalding talcum powder of gecko were 1.6， 5.2， 6.2， 6.1， 7.2 and 8.0， respectively. ROAV results showed that key components affecting odor of gecko were 2-ethyl-3，5-dimethylpyrazine， isovaleraldehyde， trimethylamine， 1-octen-3-ol， n-octanal， nonanal， 2-methylnaphthalene， γ-octanolide， 2-heptanone and phenol. Principal component analysis （PCA） significantly distinguished raw products from processed products. Orthogonal partial least squares-discriminant analysis （OPLS-DA） results showed that there were 16， 13， 16， 16， 16 differential components between raw products， fried yellow products， vinegar processed products， wine processed products， talcum powder scalding products and white wine sprayed products after scalding talcum powder of gecko. Among these differential components， there were 4 common components， namely， the contents of different odor components （2-methylnaphthalene and 2-ethyl-p-xylene） decreased， while the contents of different flavor components （2-decanone and 2，3，5-trimethylpyrazine） increased. The comprehensive scoring results showed that the odor correction effect of each processed products was in the order of talcum powder scalding products>wine processed products>vinegar processed products>fried yellow products>white wine sprayed products after scalding talcum powder. ConclusionTalcum powder scalding is a better method to improve the odor of gecko， and it can provide an experimental basis for the processing of gecko to correct the odor.