How to understand the physiological characteristics of floral fragrance?

Flowers of flowers and plants, in addition to bright colors or nectary secretion, mostly have unique fragrance. Flowers can give off fragrance, which is fragrant, rich and elegant and deeply loved by people. It has the functions of cultivating mood, restoring fatigue and sterilizing. This kind of plants are often classified as aromatic plants in flower gardening, which can be used as garden ornamental, fragrant flowers for tea or for refining essence and various drugs.

Common aromatic plants, such as vanilla, include orchids, tuberose, carnations, daffodils, musk lilies and lotus flowers; Woody plants include Osmanthus fragrans, Plum Blossoms, Chimonanthus praecox, Gardenia, Jasmine, White Orchid, Smiling, Rose, Eupatorium odoratum, Tortoise Shell and so on.

Aromatic characteristics of 1. flowers

The fragrance of flowers is due to the volatile aromatic substances in petals, which are called "aromatic oil&; quot。 The formation, species and emission habits of aromatic oils are related to plant species and also influenced by environmental conditions during flowering. Understanding the formation of floral fragrance and the habit of spitting fragrance is of guiding significance for improving the ornamental value of flowers and determining the picking time.

Secretion and Volatilization Process of (1) Aromatic Oil

It is considered that the synthesis of volatile oil often occurs in special gland cells or epithelial cells. It was observed that in the process of forming and secreting volatile oil, the glandular hairs on the leaf surface of mint first formed small oil bubbles in the cytoplasm, and then the contents of the oil bubbles were released between the epidermal cell wall and the upper stratum corneum, and the volatile oil slowly accumulated below the stratum corneum, and finally the stratum corneum broke and the volatile oil was released.

The process of volatile oil secretion of different plants is different due to different gland systems. As for the glands related to flowering, they secrete aromatic oil. However, the secretion and release process of aromatic oil in flowers may not be exactly the same as that of glands on the surface of pepper mint leaves mentioned above. The release of aromatic oil may escape through pores (Tingey et al., 1978).

(2) Characteristics of aroma emission during flower opening.

Fragrant flowers can be divided into temperament flowers and physique flowers according to the volatile characteristics of aromatic oil in their flowers.

Temperament flower refers to the volatile aromatic oil contained in this flower, which is gradually formed and volatilized with the opening of the flower, so its fragrance is the strongest at the beginning of the opening, and gradually disappears shortly after the opening of the flower, so the fragrance of this flower lasts for a short time. The aromatic plants belonging to this kind of flowers are jasmine, plum blossom, orchid, rose, wintersweet and so on.

For example, jasmine is a flower that blooms in the evening and at night. In the afternoon, the accumulation of aromatic oil in petals reached saturation. As a camellia, afternoon is the time to pick it. Jasmine is a double petal type, and the process of natural fragrance of flowers can last for more than ten hours after opening. It is observed that the volatilization of jasmine aromatic oil is strongest in the middle of the night.

Roses and flowers bloom at dawn. The content of aromatic oil gradually increased with the development of flower buds, and reached the highest at the beginning of flowering. However, from bloom to stamen discoloration, the content of aromatic oil has been greatly lost and reduced. Therefore, only those roses that have just opened and have not seen the flower heart are the most fragrant.

Plum blossom, the fragrance of flowers, is also gradually volatilized with the opening of flowers, and those flowers that are in bud and want to open at first have the strongest fragrance.

Orchids, once pollinated, the heart column will bend and the fragrance will disappear immediately. Because the fragrance is emitted by the pistil column (the joint of filament and style).

Physique flowers, the aromatic oil in flowers exists in the petals in a free state, so the petals of flowers that are not open or open for a long time are fragrant, and the fragrance of such flowers lasts for a long time until the petals wither. Belonging to this kind of aromatic plants, there are commonly white orchids, pearl orchids, generation flowers and so on. Although the flowers of these plants have been fragrant for a long time, they are also the first to bloom and have the strongest fragrance.

Whether it is temperament flower or physique flower, it is generally the first flower with the highest aromatic oil content, which is an ideal time for viewing or picking; However, the content of aromatic oil in unopened flowers or flowers that have been opened the day before is low; The "Rain Flower" that blooms in rainy days has the worst fragrance.

(3) Temperature, light, moisture and fragrance during flowering.

The fragrance of flowers is also influenced by climatic conditions, cultivation conditions and picking time. Usually, the main environment that affects the fragrance of flowers is temperature, followed by water, light and fertilizer conditions.

Most aromatic plants, when flowering, encounter high temperature and sufficient sunshine, and their flowers also have strong fragrance. Jasmine, for example, has the strongest fragrance when it blooms in July and August, while "Spring Flower" has the worst fragrance. The reason is that the flowering temperature of jasmine is 35-37℃, and it likes direct sunlight. When Hua Fu was opened, it was in the season with the highest temperature and abundant sunshine, so the flowers were the most fragrant.

White orchids also bloom in June and July, and their fragrance is stronger than that of spring flowers and autumn flowers. The fragrance of lotus is also the best, and the fragrance of early flowers and autumn flowers is relatively light.

However, many heat-labile aromatic plants concentrate on spring, autumn or winter, and in summer, not only the amount of flowers decreases, but also the fragrance is lightest. For example, in Grimson Glory Rosa Hyde Holt, the fragrance of "spring flowers" is the strongest, and that of "summer flowers" is the weakest. Chimonanthus praecox, which blooms in winter, will have a lighter fragrance if the flowering temperature is high.

Different plants and flowers contain different kinds of aromatic oils, so the suitable temperature for the formation and volatilization of aromatic oils is also different. For example, when scented tea is scented, it is noticed that the temperature required for aromatic oil emission is higher than that required for volatile aromatic oil of jasmine, pomelo, gardenia, osmanthus and magnolia.

The intensity and brightness of floral fragrance are affected by the temperature when flowering. The reason is estimated that the activities of corresponding enzymes involved in the formation of various aromatic oils are related to temperature.

During the flowering period of fragrant flowers, when there is insufficient light or rainy weather, the water content of petal tissue is too high, the accumulation of aromatic oil is relatively reduced, and the fragrance of flowers is weak. Such as the "rain flower" in the rose, the quality is poor. However, some fragrant flowers, such as orchids and smiling orchids, are not resistant to direct light. The flowers of these plants, under strong light irradiation, will affect the normal fragrance of flowers.

In case of high temperature and drought at flowering stage, due to the accelerated transpiration of petals, a large amount of aromatic oil can be lost with water evaporation, so the flower fragrance retention time of this kind of plants is relatively short.

Some aromatic plants with strict requirements on fertilizer conditions, such as Chimonanthus praecox and Jasmine, have strong fragrance when they encounter an environment with sufficient soil fertility.

2. Composition and synthesis of aromatic oil

(1) Aromatic oil types of main aromatic flowers

There are many kinds of spices extracted from the flowers of common aromatic plants. There are mainly jasmine oil, white orchid aromatic oil, rose oil, neroli oil and so on. Fragrant flowers can also be extracted with various extracts, such as magnolia extract, Michelia extract, Chimonanthus praecox extract, rose extract, osmanthus fragrans extract, narcissus extract, cordate telosma extract, jasmine extract and Lilium longiflorum extract (Table 3-3).

Table 3-3 Chemical Components of Spices

(Quoted from "Spice Manual" of Niuzhuan, 1958)

(2) Composition of aromatic oil

The aromatic oil contained in the flowers or stems, leaves and roots of plants is volatile, like liquid oil, and its specific gravity is lighter than that of water, so it is often called "plant essential oil" to distinguish it from oil.

The main components of plant essential oils are terpenoids and their derivatives, which are composed of C 10H 16, C 15H24 and C20H32. So it is based on terpenoids.

Terpenoids are a large class of compounds existing in plant organisms, including some plant pigments, vitamins, hormones and some essential oils.

The structure of terpenoids is 1- methyl -4- isopropyl cyclohexane, and the molecular formula is C 10H20, also known as "terpanes".

Terpenoids are derivatives of terpanes. In fact, they are composed of several isoprene structures connected end to end. According to the number of isoprene units contained in terpenoids, they can be divided into monoterpenes, sesquiterpenes, diterpenes, triterpenoids, tetraterpenes and polyterpenes. For example, geraniol is a monoterpene consisting of two isoprene units. It mainly exists in plants in a free state, and its cis isomer is nerol. For example, farnesol is a sesquiterpene, which is a sesquiterpene enol composed of three isoprene units. (3) biosynthesis of aromatic oil

In plants, aromatic oil is similar to alkaloid, and it is also an intermediate product of plant metabolism, which is further transformed and formed. The reason may be to attract insects, drive away pests, reduce water evaporation, heal wounds and so on.

The components of aromatic oil may be acyclic hydrocarbons formed in plants at the early stage of plant growth, and then oxidized or added with water to become alcohols under the action of related enzymes, and finally cyclized or rearranged by molecules through hydrogenation or dehydrogenation. With the change of plant growth and development stage, these components of aromatic oil constitute various terpenoid derivatives or aromatic phenols and esters.

During the biosynthesis of plant terpenoids, it was found that acetyl-CoA was used as the initial raw material and the intermediate product of respiration was acetyl-CoA, which was the raw material for further synthesis of various aromatic oils. Therefore, it also shows that the production of plant tissue aroma is the result of plant metabolic activities, and aromatic oil is the product of metabolism.

Because the activity of catalytic enzymes in plants is related to temperature and other factors, it is easy to understand that the accumulation and emission rate of aromatic oil in flowers of various aromatic plants is affected by temperature and light in the environment when flowering. It is not difficult to explain why some fragrant flowers are more fragrant than "spring flowers" in the season of high temperature and abundant sunshine from July to August.