Characterization of the key aroma compounds and microorganisms during the manufacturing process of Fu brick tea
Introduction
Fu brick tea is a special type of Chinese tea, in which microbial fermentation was involved in the manufacturing process, and it has attracted global interest owing to its special flavor and health benefits for humans (Zhang, Zhang, Zhou, Ling, & Wan, 2013). The main steps in the Fu brick tea production are steaming, piling, pressing, fermentation, and drying, with microbial fermentation considered as the key step in the development of special flavor of Fu brick tea (Mo, Zhu, & Chen, 2008; Wang, Shi, et al., 1991). Aroma is one of the most important criteria to evaluate the quality of tea, together with its appearance and taste. Ketone and ketene compounds were reported to be the most abundant components in Fu brick tea products, such as α-ionone, β-ionone, geranyl acetone, farnesyl acetone, and 6-methyl-5-hepten-2-one (Shi, Zhu, Zhang, Lin, & Lv, 2019; Xu, Mo, Yan, & Zhu, 2007). Some investigations indicated that the contents of aldehyde, terpene alcohols, ketone, and heteroxy compounds were increased significantly in Fu brick tea products when compared with raw material (Wang, Li, Liu, Wang, & Shi, 1991; Xu et al., 2007). Up to now, most of the studies mainly focused on the composition of volatile compounds in Fu brick tea products or the differential volatile compounds between raw material and finished products, whereas the dynamic changes of aroma profile during the manufacturing process, and the chemical basis of special aroma in Fu brick tea are still not well understood.
Sensory descriptive analysis is a highly developed quantitative methodology that has been used for many years to provide comprehensive sensory evaluations for food products (Stone, Sidel, Oliver, Woolsey, & Singleton, 2004). The methodology is sensitive and can be applied to many kinds of food and beverage, providing word descriptions and their intensities to compare similarities or differences between the samples. And predictive modeling allows for an empirical understanding of food flavor through regression models correlating the chemicals and sensory properties of food products. Nevertheless, how to match valuable information on the chemicals with sensory descriptors is still challenging. Recently, multivariate statistical analysis was widely used to reveal the relationship between the chemical data from instrumental analysis and sensory analysis, and to identify those chemical components that contribute most to food flavor (Seisonen, Vene, & Koppel, 2016). But there is few report related to the relationship between aroma attributes and volatile compounds in Fu brick tea. In addition, the special flavor of Fu brick tea was mainly catalyzed by the microbial enzyme secreted from microorganisms during the manufacturing process (Wang, Shi, et al., 1991). Our previous studies have been revealed the shift of microbial communities in the process (Li et al., 2017, 2019). However, the relationships between the change of volatile compounds and microbiome in Fu brick tea are also still unknown.
Therefore, the aims of the present study were to (a) elucidate the dynamic change of the volatiles profile and sensory properties during the manufacturing process, (b) illuminate the correlations between the volatiles and sensory aroma attributes, and (c) identify the key active-aroma compounds and microorganisms contributing to the characteristic aroma formation in Fu brick tea. This study is of significant importance for providing information in-depth to enhance our understanding of the mechanisms on aroma formation during the manufacturing process of Fu brick tea.
Section snippets
Chemicals
The C7–C40 n-alkanes and ethyl decanoate (99.99%) were obtained from Sigma-Aldrich (St. Louis, MO). Forty authentic standards were purchased from J&K chemical Ltd. (Beijing, China) (Table S1). All the chromatographic solvents were of chromatography grade and all of the chemicals were of analytical reagent grade unless otherwise stated.
Sample collection
Fu brick tea samples that were collected and prepared during our previous study (Li et al., 2017) were used in the present work. Briefly, primary dark tea was
Identification and quantification of volatile compounds in Fu brick tea during the manufacturing process
To illuminate the dynamic changes of volatile compounds, the tea samples collected during processing of Fu brick tea were analyzed by GC-MS with HS-SPME. In total, 72 volatile compounds were identified and were quantified in Fu brick tea (Table 1 and Table S1). All these volatile compounds could be divided into 9 classes, including 22 ketones, 16 alcohols, 11 hydrocarbons, 10 aldehydes, 5 esters, 3 heteroxy compounds, 2 phenols, 2 lactones, and 1 nitrogenous compound. Dihydroactinidiolide,
Conclusion
Characterization of the key aroma compounds and the core functional microorganisms, which contribute to the special aroma formation, is important for understanding the formation mechanism of characteristic aroma of Fu brick tea. In this study, the volatiles profile and sensory attributes of Fu brick tea were investigated during the manufacturing process. A total of 72 volatile compounds were identified and quantified in tea samples. The concentration of alcohols, lactones, ketones, phenols,
CRediT authorship contribution statement
Qin Li: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft. Yongdi Li: Investigation, Formal analysis, Validation. Yu Luo: Methodology, Writing - review & editing. Lizheng Xiao: Resources. Kunbo Wang: Resources. Jianan Huang: Conceptualization, Methodology, Validation, Writing - review & editing, Supervision. Zhonghua Liu: Conceptualization, Supervision, Project administration, Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (31871764, 31471706), National Key Research and Development Program of China (2017YFD0400803, 2018YFC1604403); and Natural Science Foundation of Hunan Province (2018JJ2181), Key Research and Development Program of Changsha (kq1902044); and the “1515 Talent Project” of Hunan Agricultural University.
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