Analysis of Characteristic Aroma Compounds in Black Tea and Exploration of the Functional Properties of Hotrienol

Abstract

Tea is a beverage produced from Camellia sinensis, and is classified into green tea, oolong tea, black tea, depending on the production process. Over 740 aroma compounds have been identified in tea, and it is the complex combination of this wide variety of components that gives each type of tea their distinctive aroma. In particular black tea is a widely enjoyed beverage all over the world, and the composition of the aroma components differs according to the origin of production. It is this region-specific composition that is a key factor in the characteristic aroma profile of each tea production area. As well as providing hydration and nutrition, black tea also serves as a luxury item in that its diverse aromatic characteristics provide a feeling of mental satisfaction. However, the physiological properties of black tea aroma remain largely unexplored. In this presentation, we will introduce our research on the physiological functions of hotrienol, an aroma component of black tea.

　Darjeeling tea (DT), known as the “champagne of teas,” is a high-quality black tea popular for its characteristic muscatel flavor. The authors conducted a non-RCT clinical study to examine the psychological and physiological effects of DT aroma inhaled intranasally. Inhalation of DT aroma reduced depression and anxiety, decreased cerebral blood flow, and increased miosis rate and peripheral skin temperature. These results suggest that DT aroma has a sedative effect on central nervous activity and activates the parasympathetic nervous system. In another study, the aroma compounds of DT were analyzed by GC-MS (SPME), revealing that DT contained higher levels of hotrienol compared to tea from other regions.

　To mimic the physiological effects of hotrienol intake by drinking black tea, we examined the effects of olfactory stimulation via the retronasal pathway through oral intake of hotrienol in a randomized, double-blind, crossover study involving 44 healthy men and women dissatisfied with their sleep. Tablets containing 0.03 mg of hotrienol, equivalent to the amount in a cup of DT, were prepared for the study. Participants consumed four tablets per day (total 0.12 mg) for two weeks, and the effects on sleep were assessed by Primary Outcomes: OSA Sleep inventory, PSQI; and Key Secondary Outcomes: sleep variables, concentrations of salivary components (CgA, oxytocin, S-IgA, cortisol). Data analysis of 33 participants who met eligibility criteria showed an increase in the score for OSA factor II (initiation and maintenance of sleep) and a reduction in overall PSQI scores, in the test group compared to the placebo group. Analysis of the data for sleep variables showed that onset latency, bed out latency, awaking time during sleep decreased, and sleep efficiency improved. However, no changes were observed in OSA factors: I (sleepiness on rising), III (frequent dreaming), IV (refreshing), V (sleep length), and in the sleep variables: number of awakenings during sleep, total sleep time, and number of postural changes. These findings suggest that two weeks of oral hotrienol intake may contribute to improvement of sleep quality. The effects of hotrienol on stress biomarkers were also examined in an exploratory study. Single intake increased salivary s-IgA and oxytocin concentrations, and long-term intake (2 weeks) decreased cortisol concentrations in participants with high stress levels (SCL 11-20 points). Study results suggest that the effects of hotrienol on sleep quality are related to its physiological functions on the central-autonomic and endocrine systems via olfactory stimulation. However, the clinical studies presented here are limited by the small number of cases and statistical multiplicity. Further clarification of the functional properties of hotrienol is expected as more reports of clinical studies are accumulated.