Chemical Diversity and Microbial Complexity of Liupao Tea Aroma: A Comprehensive Review

Liupao tea (LPT), one of China's representative fermented dark teas, develops its unique "red, heavy, aged, and mellow" flavor characteristics. This review provides a comprehensive update on LPT aroma, integrating analyses of volatile organic compounds (VOCs), associated microorganisms, odor-active compounds (OACs), and metabolic pathways of key odor-active compounds (KOACs). With over 2000 VOCs documented, predominated by alcohols (368), hydrocarbons (357), and ketones (351), the total for LPT substantially exceeds the approximately 1000 compounds typically reported for other dark teas. By combining sensory evaluation with techniques such as gas chromatography-olfactometry (GC-O) and odor activity value (OAV), KOACs, predominantly comprising alcohols, aldehydes, and methoxybenzene derivatives, were identified as key contributors to the floral, fruity, aged, stale and other notes that define LPT's characteristic aroma. The formation of the aroma compounds is closely linked to microbial metabolism and the enzymatic activities generated by microorganisms. Fungi, including Aspergillus, Rhodotorula, Geosmithia, Wallemia, Penicillium, Blastobotrys, Fusarium, and Xeromyces, and bacteria, including Burkholderia, Ralstonia, and Achromobacter, serve as the primary functional microorganisms driving fermentation and aging. This review provides a comprehensive framework for understanding the chemical and microbial complexity of LPT aroma.