The effect of maturity of tea leaves and processing methods on the formation of milky flavor in white tea - A metabolomic study.

Targeted metabolomics combined with chemometrics were applied to investigate the flavor profiles of 4 white tea samples, which were produced from different maturity fresh tea leaves with different withering methods. Mature leaves that underwent novel withering process at higher temperature (28-30℃) and humidity (75 ± 3 %) (MN) were characterized by intense milky flavor. The content of free amino acids, catechins, and soluble sugars in MN were significantly lower than that in the other 3 tea samples, resulting in a sweet and mellow taste with low bitterness. Meanwhile, MN possessed the highest intensity of milky aroma, which could be mainly attributed to the existence of dihydro-5-pentyl-2(3H)-furanone and 2-pentyl-furan as the key volatile substances with coconut and creamy fragrance. These findings provide insight into the substance foundations of milky flavor, and identified leaf maturity and processing method as the determining factors of the milk-flavored white tea (MFWT).

Comparative volatiles profiling in milk-flavored white tea and traditional white tea Shoumei via HS-SPME-GC-TOFMS and OAV analyses.

White tea is a mildly fermented tea processed with withering and drying. Milk-flavored white tea has a unique milk flavor compared to the traditional white tea. Little is known about the aromas that make white tea taste milky. Here we conducted the volatile profiling via headspace solid-phase microextraction (HS-SPME)-gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) and chemometrics to explore the key volatiles making milk-flavored white tea taste milky. Sixty-seven volatiles were identified, with 7 volatiles (OAV > 1 and VIP > 1) were characterized as the typical aromas. Green and light fruity scent volatiles, such as methyl salicylate, benzyl alcohol, and phenylethyl alcohol, were richer in TFs than MFs. Strong fruity and cheese aromas, such as dihydro-5-pentyl-2(3H)-furanone, 2-pentyl-furan, (E)-6,10-dimethyl-5,9-undecadien-2-one, and hexanal, were more abundant in MFs than TFs. Dihydro-5-pentyl-2(3H)-furanone, recognized as coconut and creamy aroma, should be the essential volatile for milky flavor. Also, (E)-6,10-dimethyl-5,9-undecadien-2-one and 2-pentyl-furan may contribute to the milk scent formation.

Study on the regulation of earthworm physiological function under cadmium stress based on a compound mathematical model.

A cadmium (Cd) stress test was carried out on Eisenia fetida in artificial soil. Six Cd concentration gradient solutions (0, 50, 100, 125, 250 and 500 mg/kg) were prepared. Two treatment groups, short-term stress and long-term stress, were established. The former lasted for 10 days, and the latter lasted for 30 days. The Biolog ECO-microplate culture method was used to determine the utilization of the 31 carbon sources by the microbes in earthworm homogenate. The total protein content (TP), peroxidase activity (POD), catalase activity (CAT), superoxide dismutase activity (SOD), glutathione peroxidase activity (GPX), glutathione-S-transferase activity (GST), malondialdehyde content (MDA) and acetylcholinesterase activity (AChE) in earthworm were determined in order to investigate the regulation of oxidative stress and the functional diversity of microbial communities in earthworms under Cd stress. By combining the entropy weight method (EW) and the technique for order preference by similarity to an ideal solution model (TOPSIS), the physiological functional indices of earthworms were assessed objectively and scientifically, and the physiological changes under the different stress periods were evaluated. The results showed that a Cd-tolerant dominant population appeared in the microbial community under Cd stress. In the short-term test, oxidative stress were more effective in coping with Cd stress than the microbial community, and oxidative stress regulated the microbial community functional diversity. Under long-term Cd stress, the regulatory effect was weak or non-existent. In this study, a new evaluation model was established to explore the regulation process of earthworm on its oxidation stress and the functional diversity of microbial communities under Cd stress, and provide a theoretical basis for revealing the detoxification mechanism of earthworms.