[An, Huimin; Huang, Jian'an; Wang, Chao; Yao, Hengbin; Liu, Zhonghua; Zheng, Xuexue; Li, Qin; Wang, Jing; Wang, C; Wang, Lianqing] Hunan Agr Univ, Key Lab Tea Sci, Minist Educ, Changsha 410128, Hunan, Peoples R China.

[Wang, Chao; Yao, Hengbin; Liu, Zhonghua; Zheng, Xuexue; Li, Qin; Huang, Jian'an; Wang, Jing] Hunan Agr Univ, Collaborat Innovat Ctr Utilizat Funct Ingredients, Changsha 410128, Hunan, Peoples R China.

[An, Huimin; Wang, Chao; Liu, Zhonghua; Li, Qin; Huang, Jian'an; Wang, Lianqing] Hunan Agr Univ, Natl Res Ctr Engn Technol Utilizat Funct Ingredien, Changsha 410128, Hunan, Peoples R China.

[Huang, Jian'an; Liu, Zhonghua] Hunan Agr Univ, Key Lab Evaluat & Utilizat Gene Resources Hort Cro, Minist Agr & Rural Affairs China, Changsha 410128, Peoples R China.

[Huang, JA; Liu, ZH ; Wang, C] H

Hunan Agr Univ, Key Lab Tea Sci, Minist Educ, Changsha 410128, Hunan, Peoples R China.

Hunan Agr Univ, Key Lab Evaluat & Utilizat Gene Resources Hort Cro, Minist Agr & Rural Affairs China, Changsha 410128, Peoples R China.

Tea;a globally cherished beverage;has garnered increased attention recently due to its numerous health benefits;such as reducing obesity;regulating blood pressure and blood sugar;and potentially preventing cancer;among other conditions (Chen et al.;Deng;Liu;Xiao;Wu;& Jiao;Yin et al.;Zhou et al.;2021). Teas are commonly classified into six main categories based on their processing methods: green tea;white tea;yellow tea;oolong tea;black tea;and dark tea (Feng et al.;2019). These categories correspond to typical processing techniques: fixing;withering;sealed yellowing;making green;fermentation;and pile-fermentation;respectively (Fig. 1 A). Teas may be further divided into four categories according to the degree of fermentation: non-fermented (green tea);semi-fermented (white;yellow;and oolong teas);fully fermented (black tea);and post-fermented (dark tea) (Zheng;Wan;& Bao;Zhu et al.;2015b). Dark tea;a distinctive post-fermented type processed with external microorganisms;primarily originates from specific regions in China (Zheng et al.;2015). Within China;dark teas are further classified into five types based on their manufacturing process and regional origin: Fu brick tea (FBT) (Shanxi and Hunan provinces);Liupao tea (Guangxi province);Kang brick tea (Sichuan province);Pu-erh tea (Yunnan province);and Qing brick tea (Hubei province) (Cheng et al.;Lv et al.;2013a). FBT has gained considerable interest due to its unique “golden flower” flavor and health benefits. The “golden flower;” originating from the cleistothecium of the fungus Eurotium cristatum;proliferates during the “flowering” phase;enhancing the color;aroma;and taste of FBT through enzyme activity and intracellular metabolism (Wang et al.;1991a;Zhang et al.;2021). This distinctive flavor is largely attributed to the sophisticated processing steps involved;including steaming;piling;pressing;flowering;and drying;with microbial fermentation playing a critical role (Mo;Zhu;& Chen;Zheng et al.;Zhu et al.;2020). The process consists of two main steps: the “piling” fermentation;which produces primary dark tea (PDT) and the “flowering” stage. Microbial activities drive transformations in FBT;including degradation;oxidation;condensation;and structural modifications (Li et al.;2018a;Zhu et al.;2020). Microorganisms catalyze bioconversion processes during the “piling” fermentation;influencing PDT's qualities and reducing certain stimulating biochemical substances. Simultaneously;the extracellular enzymes they secrete—like cellulase;pectinase;amylase;and others—convert macromolecules into smaller molecules;providing energy and carbon supplies for microbial metabolism (Li et al.;2018b;Zhang et al.;2021). Multiple kinds of microorganisms participate in the fermentation process;significantly impacting FBT's biochemical composition with E. cristatum being one of the most important players in driving its aromatic profile (Nie et al.;Xu et al.;2016). In recent years;the production and consumption of FBT have surged significantly;leading to a notable increase in its commercial value. In 2023;dark tea products;particularly those represented by FBT;capitalized on this growth trend;achieving an output value of CNY 31.04 billion (USD 4.286 billion). This marked an increase of CNY 4.18 billion (USD 578 million) from the previous year;representing the largest growth among the six major tea categories;including dry and gross teas. Dark tea ranked second in output value;trailing only behind green tea and black tea (data sourced from the Tea China Marketing Association;https://www.ctma.com.cn/;accessed on May 20;2024). The flavor profile of FBT comprises both taste and aroma;with aroma—an essential indicator of tea quality—stemming from a variety of volatile compounds (VCs). Research has validated a correlation between the concentrations of VCs and the tea aroma characteristics. In recent years;research efforts have significantly focused on VCs in FBT;revealing insights into its flavor profile. With “Fu brick tea”;“Fuzhuan tea”;“Fuzhuan brick tea”;“flavor”;and “aroma” as keywords;a literature search was conducted via the Web of Science;and the co-occurrence network graph of these keywords and the column diagram of the aroma research of FBT in recent years were analysis (Fig. 1 B&C). Overall;the number of studies investigating this has increased in recent years;reflecting a growing interest in the flavor components of FBT. However;there is currently no comprehensive review on the aroma of FBT. Therefore;a thorough overview of the latest advancements in its aroma research is necessary. This review primarily consolidates and discusses the recent advancements in understanding the sensory and chemical properties of FBT;with an emphasis on the roles of key odorants. It provides an overview of sensory evaluation methods;flavor analysis techniques;and the metabolic mechanisms of primary aroma components. This study aims to offer insights into FBT's unique aroma formation mechanism and establish a theoretical foundation for optimizing aromatic compounds and developing flavor restoration technologies for high-quality products.

园艺园林学院