Exploring flavor differences and microbial community characteristics of raw Pu-erh tea from different vintages based on flavoromics and high-throughput sequencing.

Classification of raw Pu-erh teas with different storage time based on characteristic compounds and effect of storage environment

To investigate the flavour evolution mechanism of raw Pu-erh tea (RPT) during storage, the volatile and non-volatile compounds of RPT with different storage years (1-10 years) from the same raw material origin, manufacturer, and storage location in Wenshan Prefecture, Yunnan Province, were systematically analysed by HPLC, HS-SPME-GC-MS, and OAV. The results showed that both cluster analyses based on non-volatile and volatile compounds could classify RPT of different storage years into three ageing cycles, with key turning points in the third and eighth years of storage, which is also accompanied by the colour changing from green to orange or brown, the aroma changing from a faint scent to woody and ageing, the astringency diminishing, and the sweet and mellow increasing. Theophylline was identified as the potential marker of RPT stored 1-3 years, while (-)-catechin gallate, (-)-gallocatechin gallate, quercetin, and rutin as those for a storage of 9-10 years. The volatile compounds indicate a general trend of an initial increase followed by a decrease. Forty-four key aroma compounds (OAV ≥ 1) were identified. Eucalyptol, β-Caryophyllene, 2-Amylfuran, Copaene, Estragole, and α-Terpinene originated as potential markers for RPT stored 1-3 years, while (Z)-Linalool oxide (furanoid), α-Terpineol, Terpinen-4-ol, and cis-Anethol were for RPT stored 8-10 years. This study revealed the flavour characteristics and quality changes of RPT over the course of storage, and constructed a sensory flavour wheel, providing theoretical underpinnings for the quality control and assessment of RPT.

At present, the bioactive compounds of teas are well established and there are more attempts to apply tea as a functional drink or food supplement. In addition, during tea processing, tea waste, including broken tea leaves, buds and stems, is generated and disposed to the environment. The present study aimed to compare the quality of tea waste generated in full fermentation (raw Pu-erh tea, ripen Pu-erh tea and Anhua dark tea) and non-fermentation (green tea) processings in comparison with dried butterfly pea flower (DBPF) (non-Camellia sinensis). The results showed that total flavonoid (TFC) was found to be the highest in raw Pu-erh tea at 474.470 ± 47.173 mg RE/g, followed by ripened Pu-erh tea, green tea, Anhua dark tea, and DBPF, respectively. Similarly, raw Pu-erh tea also had the highest total phenolic (TPC) at 608.090 ± 2.795 mg GAE/g, followed by green tea, Anhua dark tea, ripen Pu-erh tea, and DBPF, respectively. On the other hand, total polysaccharides (TPS) content in DBPF was the highest among samples, whereas that of raw Pu-erh tea was the lowest. According to the HPLC analysis, caffeine (CF) was the major catechin found in all types of tea waste and the total catechin content was in the order of raw Pu-erh > ripen Pu-erh tea > green tea > Anhua dark tea which was in agreement with the TPC results. However, the types of catechin were different in each sample. It is noteworthy that there was no CF in DBPF, and major catechin found in DBPF was catechin gallate. Likewise, antioxidant ability determined by DPPH was the most superior in raw Pu-erh tea, followed by green tea, ripen Pu-erh tea, Anhua dark tea and DBPF, respectively. ORAC antioxidant capacity was highest in the green tea, while that in raw Pu-erh tea, ripen Pu-erh tea and Anhua dark tea was lower but not significantly different, as expected, DBPF possessed the lowest ORAC antioxidant capacity. Finally, it can be said that the potential for tea waste to be a valuable source of antioxidants varies depending on the tea processing, and the plant variety also had an impact on the characteristics of the tea samples.

Analysis of the effect of Tenebrio Molitor rennet on the flavor formation of Cheddar cheese during ripening based on gas chromatography-ion mobility spectrometry (GC-IMS)

Steeping process is an important factor for aroma release of tea, which has rarely been investigated for the aroma changes of raw Pu-erh tea (RAPT). In addition, the comprehensive aroma characteristics identification of RAPT infusion is necessary. In this study, GC-IMS coupled with principal component analysis (PCA) was used to clarify the difference of volatile profiles during the steeping process of RAPT. Furthermore, the volatiles contained in the RAPT infusion were extracted by three pretreatment methods (HS-SPME, SBSE, and SAFE) and identified using GC-O-MS. According to the odor activity value, 28 of 66 compounds were categorized as aroma-active compounds. Aroma recombination and omission experiments showed that "fatty", "green", "fruity", and "floral" are considered to be the main aroma attributes of RAPT infusion with a strong relationship with 1-octen-3-one, 1-octen-3-ol, (E)-2-octenal, β-ionone, linalool, etc. This study will contribute a better understanding of the mechanism of the RAPT steeping process and volatile generation.

Effects of enhanced fermentation with high-yielding strains of Tetramethylpyrazine on flavor quality of Douchiba

New insights into optimal storage conditions for raw Pu-erh tea: modulating post-fermentation flavor via microbial metabolism under controlled water activity.

Variations of volatile flavors and microbial communities in Chinese Chaozhou pickle during natural fermentation revealed by GC-IMS and high-throughput sequencing

In order to explore the effects of extrusion processing on characteristic flavor compounds of pea flour and improve the flavor quality, in this study, electronic nose(E-nose) and gas chromatography-ion mobility spectrometry(GC-IMS) were used to investigate the effects of extrusion temperatures (120, 150, 180 ℃) on volatile flavor compounds of pea flour and compared with unextruded pea flour. The flavor differences between samples with different extrusion temperatures can be evaluated objectively by the electronic nose system. A total of 53 volatile substances in 8 compounds, including aldehydes, alcohols, ketones, acids, esters, pyrazines, furans and ethers were identified by GC-IMS. The relative content of alcohols, ketones, acids, esters, ethers decreased, the relative content of pyrazines and furans increased. The relative content of characteristic beany flavor compounds such as trans-2-octenal, hexanal, 1-octene-3 alcohol, n-hexanol, 1-pentanol, n-butanol and 2-pentylfuran decreased by 23.53%, 33.23%, 50.44%, 88.82%, 77.69%, 84.51%, 26.19%, respectively and the relative content of 2, 5-dimethylpyrazine, 2-methylpyrazine and 2-furanmethanol with roasted flavor increased by 16.16, 23.92, and 7.95 times, respectively at the extrusion temperature of 180 ℃. Relative odor activity value (ROAV) showed that n-nonanal, 3-methylbutanal, hexanal, n-octanal, 1-octen-3-ol, heptanal, ethyl acetate, n-butyraldehyde, trans-2-octenal, 2-pentylfuran, 2-ethylfuran and n-hexanol were the characteristic flavor compounds of raw pea flour. Principal component score determined that the flavor of the 180 ℃ extruded sample was the best.

This study analyzed the flavor compounds in the meat of four indigenous breeds of Chinese sheep through the use of gas chromatography-ion mobility spectrometry (GC-IMS). GC-IMS provided information on the characteristics and strength of 71 volatile flavor compounds (monomers and dimers), with aldehydes, alcohols and ketones being the most abundant in all types of sheep meat. The compounds with higher intensity peaks in the sheep meat were aldehydes (n-nonanal, octanal, heptanal, 3-methylbutanal, and hexanal), alcohols (1-octen-3-ol, hexanol, and pentanol), ketones (3-hydroxy-2-butanon, 2-butanone, and 2-propanone), esters (methyl benzoate), and thiazole (trimethylthiazole). The volatile flavor components in the meat of the different breeds of sheep obtained via GC-IMS were further differentiated using principal component analysis. In addition, orthogonal partial least squares discriminant analysis (OPLS-DA) and variable importance on projection (VIP) were used to determine the characteristic flavor compounds in the meats of different breeds of sheep, and 21 differentially volatile components were screened out based on having a VIP above 1. These results indicate that GC-IMS combined with multivariate analysis is a convenient and powerful method for characterizing and discriminating sheep meat.

In this study, electronic nose (E-Nose) and gas chromatography-ion mobility spectrometry (GC-IMS) were used to analyze the effects of different amounts of onion paste (0, 10, 20, 30, 40, and 50%) on the flavor of naan (a different kind of bread with a round/circle shape, and naan is largely taken as favorite food in Xinjiang Uyghur Autonomous Region, China). The results showed that the E-Nose analysis could distinguish six kinds of naan flavor generated due to different amounts of onion paste. A total of 24 known volatile components were detected by GC-IMS, including alkanes, alkenes, phenols, esters, ketones, aldehydes, heterocycles, etc. Cluster analysis and principal component analysis (PCA) showed that six kinds of naan with different amounts of onion paste could be distinguished by flavor compounds. The reliable results derived by GC-IMS, PCA, and linear discriminant analysis in this study can provide precise theoretical guidance for revealing the formation of the flavor of similar bread products like naan. Novelty impact statement Electronic nose and gas chromatography-ion mobility spectrometry (GC-IMS) were used to analyze the effects of different amounts of onion paste (0, 10, 20, 30, 40, and 50%) on the flavor of round/circle bread (naan). Electronic nose and GC-IMS analysis showed that different flavors and 24 known volatile components were generated due to different amounts of onion paste. Cluster analysis and principal component analysis (PCA) showed that six kinds of naan with different amounts of onion paste could be distinguished by flavor compounds.

This study investigated the effect of different processing methods (boiling, oil boiling, and stir frying) on the flavor of hoki steak soups. The quality of different fillet broths was explored by pH, Thiobarbituric acid reactive substances (TBARS), and color. E-nose, E-tongue, and gas chromatography-ion mobility spectrometry (GC-IMS) combined with free amino acids (FAAs) were used to analyze the flavor of hoki steak soups. Key compounds were screened by relative odor activity value (ROAV). The variable influence on projection (VIP) was used to identify the differential compounds. The E-nose and E-tongue were able to distinguish hoki steak soups. A total of 47 volatile compounds were characterized by GC-IMS. n-Pentanal (M) was the key component for the difference between hoki steak soups. There were six substances with ROAV ≥ 1. The results showed that the hoki steak soup boiled for 2 h in the stir-frying group had a lower fishy odor.

Infusions prepared from raw pu-erh tea (RAPT) and ripened pu-erh tea (RIPT) showed remarkable aroma differences. Predominant odorants in RAPT and RIPT infusions were identified and compared by the combined use of gas chromatography-olfactometry, aroma extract dilution analysis, odor activity values (OAVs), and multivariate analysis. A total of 35 and 19 odorants (OAV > 1) were detected in RIPT and RAPT, respectively. Odorants in RAPT and RIPT are significantly different in both odor properties and aroma compound intensities. Overall, RAPT contained a complex variety of chemical classes with diverse odors and moderate odor intensities, while RIPT is dominated by structurally and organoleptically similar compounds with high potency. Specifically, stale and musty smelling methoxybenzenes contributed the most to RIPT, while floral-, sweet-, and woody-smelling terpene alcohols, terpene ketones, and phenolic compounds were the predominant odorants in RAPT. Orthogonal partial least squares discriminant analysis revealed that linalool, α-ionone, 1,2,4-trimethoxybenzene, 1,2,3-trimethoxy-5-methylbenzene, 1,2,3,4-tetramethoxybenzene, and 1,2,3-trimethoxybenzene underwent remarkable changes during pile fermentation and could be used as potential odor-active markers for RIPT and RAPT discrimination. The comprehensive aroma characterization of pu-erh tea and determination of the effect of pile fermentation on odorant alteration herein will provide guidance for pu-erh tea flavor quality control and evaluation.

As a potential raw material with a variety of bioactive compounds, Pu-erh raw tea can produce rich flavor and health benefits through natural fermentation or microbial fermentation in traditional processing. However, the traditional fermentation process has some problems such as a long fermentation period and unstable quality. Monascus, a kind of fungus used in both medicine and food, has been proved to have many beneficial effects such as lowering cholesterol and regulating blood lipids. Therefore, in this study we investigated whether the fermentation of mixed monascus could significantly improve the flavor quality and lipid-lowering activity of Pu-erh raw tea. We added four kinds of monascus to unfermented Pu-erh raw tea (UT) to obtain a fermented Pu-erh raw tea (FT). The quality of the two tea samples was determined and an in vitro lipid-lowering experiment was conducted. The results show that the contents of water extractives, flavone, trans-catechins (GCG and CG), theabrownins, and caffeine in FT are significantly higher than those in UT, increasing by 19.41%, 14.47%, 18.76%, 29.82%, and 10.67%, respectively. In terms of aroma, linalool was the characteristic compound of UT, presenting a floral note. D-Limonene was the key characteristic substance of FT, manifested as lemon, toast, and wood. In terms of taste, FT has a high content of bitter amino acids and caffeine, a low content of catechins, and is rich in carbohydrate substances, forming a characteristic mild and mellow slightly bitter taste with reduced astringency. In addition, the relative contents of active substances with lipid-lowering effects such as quercetin, quercitrin, ascorbic acid, and sorbitol in FT were higher than those in UT, increasing by 83.09%, 81.73%, 89.86%, and 92.76%, respectively. The effect of FT on regulating cellular lipid metabolism was superior to UT based on cell experiments. The research results provide a scientific basis for the deep processing and functional development of Pu-erh raw tea.

Flavor characteristics of semi-dried yellow croaker (Pseudosciaena crocea) with KCl and ultrasound under sodium-reduced conditions before and after low temperature vacuum heating.