Plant extracts are natural plant products that are made from natural plants and enriched with one or more components of the plant using advanced physical and chemical methods.

In the early days, plant extracts were used as raw materials for health food and pharmaceuticals. So far with the pursuit of and trust in natural health products, plant extracts are increasingly used in the food, cosmetic, dyeing and feed industries. This paper focuses on the possibilities of the application in tobacco flavoring.

The use of tobacco flavoring may date back to 1519 when the indians added Orange Oil to tobacco to enhance the flavour of the smoke.

In the 1950s, the world's major tobacco companies and research institutions began to focus on enhancing the flavour of cigarette smoke, some basic flavorings as the earliest raw materials for cigarette flavoring began to be used for tobacco flavoring. With the breakthrough increasing of raw materials for cigarette flavoring, some traditional raw materials for cigarette flavoring such as rum, liquorice extract, rose oil, vanilla infusion, cinnamon oil, etc are still widely used in cigarette flavoring.

The role of adding flavoring to tobacco is to reduce the irritation, so that to improve the after taste, reduce the harm, and improve some of the physical properties of tobacco, such as moistenability, flexibility, combustibility and mould-proof, the flavoring raw materials used should meet for the conditions, such as higher boiling point, non-volatile, etc.

There is a wide range of natural tobacco flavoring available, which can be divided into the following eight categories according to their source.

● Tobacco's own flavoring, a mixture of volatile aromatic components extracted mainly from the flowers, leaves, stems, roots and fruits of the herb.

● Fruit-based spices, including lemon, bergamot, orange, kumquat, fig, dill, strawberry,  jujube, wild jujube, etc.

● Tea-based spices.

● Floral fragrances, including rose, jasmine, cinnamon, lily, lavender, chrysanthemum, acacia, lilac, ylang-ylang, bergamot, orange, wild chrysanthemum, humulus lupulus, honeysuckle, etc.

● Leaf-based spices, including aromatic leaves, orange leaves, eucalyptus leaves, loquat leaves, camphor leaves, etc.

● Seaweed-based spices.

● Fungi spices, including shiitake mushrooms, etc.

● Plant-based spices, including Scutellaria baicalensis, the root bark of the peony tree, fennel, etc.

"Smoking&Health" has become a major problem for the tobacco and pharmaceutical industries, and is a major concern for society today. Although the correlation between smoking and the occurrence of certain diseases in humans has yet to be confirmed by further extensive research, it has been long known that the tobacco and its harmful substances contained in smoke cause symptoms such as throat discomfort, cough and sputum.

There are many different sources of extraction for tobacco flavoring and it is important to find the best natural plants for industrial production and application and to find the best extraction process.

The research and development of medicinal cigarettes began in China in the 1950s and has largely gone through two stages. The first stage of "medicinal cigarettes" was made by the traditional Chinese medicine "smoke therapy" to add some kind of Chinese medicine or herbal infusion cream to tobacco. The second stage was at the end of the 1980s, when the focus was on reducing the harmful ingredients in cigarettes and building the body to some extent, focusing on the harmony between tobacco and medicine, maintaining the original colour, flavoring and taste of the tobacco, and giving full play to the characteristics of Chinese herb medicine in conditioning and health care to treat and improve one's immunity.

The principle of Chinese herb additives for tobacco

Tobacco additives can act in one or more of the following ways.

(i) The initial form is damaged or changed by combustion and high temperature synthesis so that it produces a transmission effect on the tasting and flavoring aspects. For example, sugars or concentrated sugars can be added to reduce the irritation of the smoke.

(ii) The initial form is destroyed or changed prior to combustion and high temperature synthesis, creating an intermediate form. For example, sugars, amino acids and concentrated sugars can applied to Burley tobacco leaves prior to curing.

(iii) Changes, distillation and pyrolysis in the morphology of some substances due to high temperatures during smoking, such as the use of vanillin, rose essence, etc.

(iv) The basic form is not altered, carried and transmitted by mainstream smoke.

(v) The basic form remains unchanged and is transmitted directly to the mouth, such as the menthol flavoring threads in filter sticks. When cigarettes containing Chinese herb additives are smoked, the plant extracts are heated by different temperature gradients in the cigarette and their active ingredients can be distilled, vaporised, volatilised and sublimated to form particulate and gas phase components, which capture free radicals in the smoke, reduce the production of harmful substances and also act on the respiratory system. Gas particles of different particle sizes are either deposited in the respiratory tract or absorbed into the bloodstream by the alveoli, to affect on the partial or whole body and reduce the discomfort and harm caused by smoking.

Research on the extraction technology of active ingredients of Chinese herb medicines

Research on Chinese herb additives began with the extraction of the active ingredients of herb medicines. Traditional extraction methods include decoction, maceration, percolation and reflux methods, which generally have disadvantages such as low extraction rate of active ingredients, low clearing rate, long production cycle, high energy consumption and high solvent usage.

With the rapid development of modern industrial engineering technology, Chinese medicine engineering technology has made great progress, and some high-tech engineering technology is being continuously borrowed into the production of Chinese medicine, which on the one hand makes the production of Chinese medicine more in line with the traditional Chinese medicine theory and ensures the quality requirements, and on the other hand also improves the utilization rate of existing Chinese herb medicine resources. Semi-bionic extraction method, supercritical fluid extraction method, ultrasonic extraction method, microwave extraction technology are adopted in modern Chinese herb medicine extraction.

Evaluation study on the feeding of Chinese herb additives for tobacco

For cigarette additives, they always focus on modifying and adjusting the flavour of the smoke to make the flavour of the cigarette more pure and pleasing. The identification of additives for cigarettes differs from that of cosmetics and food additives in that additives for cigarettes are mixed into the tobacco and are felt through burning, pyrolysis and dry distillation of the tobacco during smoking quality evaluation.

Therefore, the identification of cigarette additives is not enough just by sniffing, but also by the evaluation of the smoking quality staff. When Chinese herb additives are added to new blended type cigarettes, they are mainly evaluated by aroma and flavoring, to obtain the right additives and reasonable proportion. Tobacco and its products are mainly evaluated by sensory evaluation, through the human senses to feel the effect of smoke, that is, through the human sense of smell and taste to evaluate the inherent quality of the product.

These sensory perceptions, of course, have to be carried out by the nervous system, memory, and verbal expression, and only professionally trained people can be involved in the smoking quality evaluation.

Pyrolysis study of Chinese herb additives for tobacco

As a special hobby, smokers can get certain satisfaction from cigarettes, mainly including colour, flavour and taste, i.e. beautiful colour, rich fragrance, mellow taste, no miscellaneous gas and irritation, but truly reflect its value mainly through smoking.

When the cigarette is lit, a combustion zone is formed at the end of the cigarette. During smoking, there are two different combustion methods, suction combustion and natural smoldering combustion between smokings. At the same time, according to the distribution of combustion temperatures and the reactions that take place in the different zones, there are two main reaction zones: the high temperature combustion zone, the medium temperature pyrolysis zone, the distillation heat absorption zone and the low temperature condensation zone. When the temperature rises to 300°C, the volatile substances from the cigarette enter the smoke; at 450°C, the tobacco is coked; at 600°C, the tobacco is ignited and starts to burn; the maximum temperature during smoking can reach 900°C.

During the cigarette combustion and smoking process, the additives and chemical components of cigarettes undergo a series of processes such as distillation, pyrolysis, synthesis, polymerisation and condensation, of which pyrolysis is an important part of the cigarette combustion process. The study of the pyrolysis behaviour of cigarette additives in the smoke can help to understand the role of cigarette additives, such as flavorings and tobacco chemicals, in the cigarette combustion process, and is important for the optimal design of cigarette flavoring formulations.

When Chinese herb additives are added to cigarettes, the reason why they can improve the smoking quality of the cigarettes or play certain medicinal effects in the cigarettes is whether its active ingredients enter the smoke as a whole during the cigarette combustion and smoking process or whether they are partially cracked, and whether some other useful substances are produced during the combustion process. Therefore, it is important to study whether the additives enter the smoke as a whole during the cigarette combustion and burning process or whether they are partially cracked.