**3. Chemical constituents of scented tea**

Polyphenols are an important component of tea, accounting for around 18–36% of the tea dry weight. Catechins are the main components of tea polyphenols, accounting for around 70–80% of the total tea polyphenols. Catechins can be categorised according to molecular structure into four types: epicatechin, epigallocatechin, epicatechin-3-gallate and epigallocatechin-3-gallate as shown in **Figure 2**. Tea polyphenols have strong antioxidant effects that are significantly greater than those of vitamins C and E, although they have synergistic effects with vitamin C and E, with anti-ageing effects [36, 37].

**Figure 2.**

*Structure of catechins EC, epicatechin; EGC, epigallocatechin; ECG, epicatechin-3-gallate and EGCG, epigallocatechin-3-gallate.*

In addition to polyphenols, the chemical constituents of scented tea also include glycosides, flavonoids, lactones, coumarins, quercetin, terpenes and other compounds. Chemical studies on jasmine have shown that the main functional components of jasmine include nearly 100 compounds, such as volatile oils, fatty acids, glycosides, terpenoids, lignans and alkaloids [38]. According to the 'Compendium of Materia Medica', decoction of jasmine can be used to treat dysentery and abdominal pain and can also be used as an eye wash to treat conjunctivitis [39].

The chemical constituents of lily scented tea were examined by ethanol reflux extraction and the main components were found to be β-sitosterol, stigmasterol and emodin [40]. Among these, β-sitosterol lowers cholesterol, relieves cough and eliminates phlegm, inhibits tumour formation and inhibits skin ulceration. Sterols have high nutritional value and strong physiological activity and are commonly used in the pharmaceutical, cosmetics, animal growth regulators and food industries. Emodin can be used as a laxative and has anti-bacterial, anti-cough, anti-tumour and blood pressure lowering effects.

Studies on the chemical constituents of osmanthus scented tea show that the volatile components mainly include hexadecanoic acid, methyl docosatrienoate, camphor oil and isomenthone [41]. Studies have shown that the flavonoids in osmanthus scented tea have good anti-bacterial activity, especially against *Escherichia coli* and *Staphylococcus aureus*. Studies on melanin derived from osmanthus scented tea seed coat showed that it has good anti-oxidant activity and can effectively prevent skin ageing [42].

Rose scented tea is rich in vitamins A, B and C and as well as amino acids, polysaccharides, alkaloids and other functional ingredients. The vitamin C content of roses is very high and can reach eight times that of kiwifruit, 20 times that of sea buckthorn and 700 times that of apples. Rose scented tea contains 16.33% protein and is rich in amino acids. Rose also contains a variety of unsaturated acids, including the essential fatty acids linoleic acid, linolenic acid and oleic acid, which together account for 99.75% of the total unsaturated fatty acids [43]. Rose is rich in dietary fibre, rose flavonoids and amino acids and can reduce blood lipids and blood sugar. It is also rich in trace elements including zinc, copper and manganese. These are important elements of superoxide dismutase and selenium, which is an important element of thiooxyreductase and glutathione peroxidase. These enzymes can improve the immune system and have good anti-oxidant effects [44].

The active components of honeysuckle mainly include phenolic acids, flavonoids, volatile oils and triterpenoid saponins, among which phenolic acids are important secondary metabolites in honeysuckle [45, 46]. Honeysuckle has good anti-oxidant activity due to its multiple phenolic hydroxyl groups in the structure [47]. Honeysuckle scented tea contains quercetin, luteolin, kaempferol, β-sitosterol, wogonin and other components, giving it fever-reducing and cleansing properties. It has also been shown to have preventive effects on coronavirus disease 2019 [48].
