A comparative analysis for the volatile compounds of various Chinese dark teas using combinatory metabolomics and fungal solid-state fermentation

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.

Aged fragrance formed during the post-fermentation process of dark tea at an industrial scale

Although aged fragrance is the most outstanding quality characteristic of dark tea, its formation still is not much clear. Thus, the volatiles of Qingzhuan tea (QZT) during the whole post-fermentation process were investigated at an industrial scale. The results showed that most of volatiles increased during pile-fermentation of QZT and weakened during aging storage, but some new volatiles were produced through aging storage. Hexanal, (E)-2-hexenal, (E)-2-decenal, 2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde, heptanal, (E)-2-octenal, (R)-5,6,7,7a-tetrahydro-4,4,7a-trimethyl-2(4H)-benzofuranone, ionone, 2-heptanone, 3-ethyl-4-methyl-1H-pyrrole-2,5-dione, (R,S)-5-ethyl-6-methyl-3-hepten-2-one, cis-5-ethenyltetrahydro-5-trimethyl-2-furanmethanol, and linalool generated by pile-fermentation should be the basic volatiles of aged fragrance in QZT, and 4-(2,4,4-trimethyl-cyclohexa-1,5-dienyl)-but-3-en-2-one, 6-methyl-5-heptene-2-one, safranal, guaiene, trans-2-(2-propynyloxy)-cyclohexanol, nonanal, and 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2-butanone formed during aging storage should be the transformed volatiles of aged fragrance in QZT, which together constitute the characteristic components of aged fragrance. Notably, 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2-butanone, 6-methyl-5-heptene-2-one, and safranal were selected as the key volatiles of QZT. These results contribute to understand better the formation of agedfragrance in dark tea.

Biotransformation of green tea (Camellia sinensis) by wine yeast Saccharomyces cerevisiae

Wine yeast Saccharomyces cerevisiae 71B was used in fermentation of green tea to modulate the volatiles and nonvolatiles. After fermentation, higher alcohols, esters, and acids, such as isoamyl alcohol, isobutanol, ethyl octanoate, ethyl decanoate, octanoic, and decanoic acids were generated. Some key aroma compounds of tea including linalool, hotrienol, dihydroactinidiolide, and 2-phenylethanol increased significantly. Among these compounds, linalool and 2-phenylethanol increased by 1.3- and 10-fold, respectively, which impart floral and fruity notes to fermented green tea. Alkaloids including caffeine, theobromine, and theophylline were reduced significantly after fermentation, while the most important free amino acid in tea, theanine, was not metabolized by S. cerevisiae. Tea catechins decreased whereas gallic and caffeic acids increased significantly, resulting in the unchanged antioxidant capacity of the fermented green tea. Hence, this work highlighted the potential of using S. cerevisiae to modulate green tea aroma and nonvolatiles. PRACTICAL APPLICATION: A novel fermented tea is produced by yeast fermentation. Saccharomyces cerevisiae led to significant changes in tea volatiles and nonvolatiles. Antioxidant capacity remained stable after fermentation.

Bioprocessing of soybeans (Glycine max L.) by solid-state fermentation with Eurotium cristatum YL-1 improves total phenolic content, isoflavone aglycones, and antioxidant activity

In this study, soybean (Glycine max L.) was bioprocessed with fungal strain Eurotium cristatum YL-1 by using the solid-state fermentation (SSF) technique. The effect of SSF on total phenolic content (TPC), isoflavone compositions, and antioxidant activity of soybean during different fermentation periods was evaluated. Results showed that TPC and isoflavone aglycones were significantly increased, whereas glucoside isoflavones were remarkably reduced during SSF. After 15 days of SSF, the TPC, daidzein, genistein, and total aglycones of soybeans were approximately 1.9-, 10.4-, 8.4-, and 9.4-fold higher, respectively, than those of non-fermented soybeans. During SSF, β-glucosidase activity was very high, whereas α-amylase and protease activities were at moderate levels, and cellulase activity was relatively low. A highly positive correlation was found between TPC and the activities of α-amylase (correlation coefficient R² = 0.9452), β-glucosidase (R² = 0.9559), cellulase (R² = 0.9783), and protease (R² = 0.6785). Linear analysis validated that the β-glucosidase produced by E. cristatum contributed to the bioconversion of soybean isoflavone glucosides into their aglycone forms. The DPPH radical and ABTS˙⁺ scavenging activity, reducing power, and ferric reducing antioxidant power of soybeans were considerably enhanced during SSF. Principal component analysis and Pearson's correlation analysis verified that the improvement in TPC and isoflavone aglycone content during SSF was mainly responsible for the improved antioxidant capacity of soybeans. Thus, our results demonstrated that solid-state bioprocessing with E. cristatum is an effective approach for the enhancement of the TPC, isoflavone aglycones, and antioxidant capacity of soybeans. Bioprocessed soybean products might be a healthy food supplement rich in antioxidants compared with non-fermented soybean and thus could be a source of natural antioxidants.

Solid-state bioprocessing with Eurotium cristatum is an effective approach for the enhancement of total phenolic content, isoflavone aglycones, and antioxidant activity of soybeans.

Anti-obesity effects of instant fermented teas in vitro and in mice with high-fat-diet-induced obesity

Obesity is a chronic metabolic disorder that is associated with higher risks of developing diabetes and cardiovascular disease. Chinese dark tea is a fermented beverage with many biological effects and could be considered for the management of obesity. This study is aimed to assess the possible anti-obesity properties of instant dark tea (IDT) and instant pu-erh tea (PET) in high fat diet (HFD)-fed mice. Male C57BL/6 mice were divided into 5 groups. They received low-fat diet (LFD), HFD, HFD supplemented with drinking IDT infusion (5 mg mL-1), PET infusion (5 mg mL-1) or water for 8 weeks. The results showed IDT exhibited better inhibitory effect than PET on body weight gain and visceral fat weights. IDT also improved the serum high-density lipoprotein cholesterol (HDL-C) level, but decreased the low-density lipoprotein cholesterol (LDL-C) and leptin levels more effectively than PET. Both IDT and PET lowered the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the plasma and significantly increased the ratio of albumin to globin (A/G) in the serum compared to the control group. IDT treatment reduced the malondialdehyde (MDA) level in the liver. Histomorphology evidenced that the liver tissue architecture was well preserved by IDT administration. Moreover, IDT regulated the expression of obesity-related genes more effectively than PET. Overall, the present findings have provided the proof of concept that dietary IDT could provide a safer and cost-effective option for people with HFD-induced obesity.

Comparison of Potent Odorants in Raw and Ripened Pu-Erh Tea Infusions Based on Odor Activity Value Calculation and Multivariate Analysis: Understanding the Role of Pile Fermentation

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.

Multistarter fermentation of glutinous rice with Fu brick tea: Effects on microbial, chemical, and volatile compositions

A higher fermentation efficiency was achieved, using multistarter fermentation of glutinous rice supplemented with Fu brick tea (FGR-FBT), than when using traditional fermentation. The effects of multistarter fermentation on the microbial, chemical, and volatile compositions were determined. When FBT was incorporated during glutinous rice fermentation, increased population of yeasts and fungi, as well as enhanced α-amylase, proteinase and β-glucosidase activities, were observed. Specific fungi were isolated and identified as Aspergillus spp., which are known to secrete extracellular enzymes that modify the chemical properties, including ethanol levels, pH, total acids, and total soluble solids. The aroma profile of fermented glutinous rice was studied in the absence and presence of FBT, using HS-SPME-GC-MS and the electronic-nose. This analysis indicated that 35 characteristic volatile compounds were only found in FGR-FBT. The results show that FBT can be added during the fermentation of food products to enhance microbial biotransformation and modify flavour metabolism.

Elucidation of Infusion-Induced Changes in the Key Odorants and Aroma Profile of Iranian Endemic Borage ( Echium amoenum) Herbal Tea

Infusion-induced changes in the aroma and key odorants and their odor activity values of Iranian endemic herbal (Gol-Gavzaban) tea obtained from shade-dried violet-blue petals of borage ( Echium amoenum) were studied for the first time. Two hot teas and one cold tea were investigated and coded as 4MN (4 min/98 °C), 16MN (16 min/98 °C), and 24HR (24 h/ambient temperature), respectively. Aromatic extracts of the tea samples were isolated by the liquid-liquid extraction method and analyzed by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) for the first time. According to the results of the aroma profiling, a total of 35 common aroma compounds comprising alcohols, acids, volatile phenols, lactones, aldehydes, ketone, pyrroles, and furans were identified and quantified in the tea samples. Indeed, it is worth noting that the aroma profiles of the borage teas were similar. However, the effects of the infusion techniques were clearly different as observed on the content of each individual and total compounds in the samples. The highest mean total concentration was detected in 24HR (266.0 mg/kg), followed by 16MN (247.1 mg/kg) and 4MN (216.1 mg/kg). 1-Penten-3-ol was the principal volatile component in all borage teas. On the basis of the result of the flavor dilution (FD) factors, a combined total of 22 different key odorants was detected. The potential key odorants with regard to FD factors in all samples were prevailingly alcohols, acids, and terpenes. The highest FD factors were observed in 2-hexanol (2048 in 4MN and 24HR; 1024 in 16MN) and 1-penten-3-ol (2048 in 24HR; 1024 in 4MN and 16MN) in samples providing herbal and green notes. Principal component analysis (PCA) showed that the tea samples could clearly be discriminated in terms of their aroma profiles and key odorants. The findings of the current study demonstrate that the tea preparation conditions have a significant impact on the organoleptic quality of borage tea.

Omics in traditional vegetable fermented foods and beverages

For a long time, food microbiota has been studied using traditional microbiological techniques. With the arrival of molecular or culture-independent techniques, a strong understanding of microbiota dynamics has been achieved. However, analyzing the functional role of microbial communities is not an easy task. The application of omics sciences to the study of fermented foods would provide the metabolic and functional understanding of the microbial communities and their impact on the fermented product, including the molecules that define its aroma and flavor, as well as its nutritional properties. Until now, most omics studies have focused on commercial fermented products, such as cheese, wine, bread and beer, but traditional fermented foods have been neglected. Therefore, the information that allows to relate the present microbiota in the food and its properties remains limited. In this review, reports on the applications of omics in the study of traditional fermented foods and beverages are reviewed to propose new ways to analyze the fermentation phenomena.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

: Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.