Siraitia grosvenorii

Siraitia grosvenorii is an herbaceous perennial vine of the Cucurbitaceae (gourd) family, native to southern China and northern Thailand. The plant is cultivated for its fruit, whose extract is nearly 300 times sweeter than sugar and has been used in China as a natural low-calorie sweetener for cooling drinks, and in traditional Chinese medicine to treat diabetes and obesity.

The plant's fruit is often called in English language publications luo han guo or luo han kuo (from the Chinese luóhàn guǒ, 罗汉果/ 羅漢果). It may also be called la han qua (from Vietnamese la hán quả), arhat fruit, Buddha fruit, monk fruit, or longevity fruit (although this name has been used for several other fruits).

The scientific species name honors Gilbert Grosvenor who as president of the National Geographic Society helped to fund an expedition in the 1930s to find the living plant where it was being cultivated.

Description
The vine attains a length of 3 to 5 m, climbing over other plants by means of tendrils which twine around anything they touch. The narrow, heart-shaped leaves are 10–20 cm long. The fruit is round, 5–7 cm in diameter, smooth, yellow-brownish or green-brownish in colour, containing striations from the fruit stem end of the furrows with a hard but thin skin covered by fine hairs. The inside of the fruit contains an edible pulp, which, when dried, forms a thin, light brown, brittle shell about 1 mm in thickness. The seeds are elongated and almost spherical.

The fruit is sometimes mistaken for the unrelated purple mangosteen.

The interior fruit is eaten fresh, and the bitter rind is used to make tea.

The monk fruit is notable for its sweetness, which can be concentrated from its juice. The fruit contains 25 to 38% of various carbohydrates, mainly fructose and glucose. The sweetness of the fruit is increased by the mogrosides, a group of triterpene glycosides (saponins). The five different mogrosides are numbered from I to V; the main component is mogroside V, which is also known as esgoside. The fruit also contains vitamin C.

Cultivation
Germination of seeds is slow and may take several months. It is grown primarily in the far southern Chinese province of Guangxi (mostly in the mountains near Guilin), as well as in Guangdong, Guizhou, Hunan, and Jiangxi provinces. These mountains lend the plants shade and often are surrounded by mists which protect the plants from the sun. Nonetheless, the climate in this southern province is warm. The plant is rarely found in the wild, so it has been cultivated for hundreds of years.

Records as early as 1813 mention the cultivation of this plant in the Guangxi province. At present, the Guilin mountains harbor a plantation of 16 sqkm with a yearly output of about 10,000 fruits.Most of the plantations are located in Yongfu County and Lingui County.

Longjiang Town in Yongfu County has acquired the name "home of the Chinese luohanguo fruit"; a number of companies specialised in making luohanguo extracts and finished products have been set up in the area. The Yongfu Pharmaceutical Factory is the oldest of these.

Traditional uses
The plant is most prized for its sweet fruits, which are used for medicinal purposes and as a sweetener. The fruits are generally sold in dried form, and traditionally used in herbal tea or soup.

Non-toxicity
No incidents of negative side effects of luohan guo have been reported. Multiple self-designated generally recognized as safe (GRAS) notices have been received by the US Food and Drug Administration (FDA) without objection. One notification for GRAS status for using monk fruit juice concentrate to sweeten edible products was submitted to the FDA in 2009. No restrictions on consuming the fruit or its extracts were made.

Active agents
The sweet taste of the fruit comes mainly from mogrosides, a group of triterpene glycosides that make up about 1% of the flesh of the fresh fruit. Through solvent extraction, a powder containing 80% mogrosides can be obtained, the main one being mogroside-5 (esgoside) Other similar agents in the fruit are siamenoside and neomogroside.

Recent research suggests isolated mogrosides have antioxidant properties and may have limited anticancer effects.

Mogrosides have also been shown to inhibit induction of Epstein-Barr virus in vitro.

The plant also contains the glycoprotein momorgrosvin, which has been shown to inhibit ribosomal protein synthesis.

Traditional processing
Luohan guo is harvested in the form of a round, green fruit, which becomes brown on drying. It is rarely used in its fresh form, as it is hard to store. Furthermore, it develops a rotten taste on fermentation, which adds to the unwanted flavours already present.

Thus, the fruits are usually dried before further use and are sold in precisely this fashion in Chinese herbal shops. The fruits are slowly dried in ovens, preserving them and removing most of the unwanted aromas. However, this technique also leads to the formation of several bitter and astringent flavors. This limits the use of the dried fruits and extracts to the preparation of diluted tea, soup, and as a sweetener for products that would usually have sugar or honey added to them.

The Procter & Gamble process
The process for the manufacture of a useful sweetener from luo han guo was patented in 1995 by Procter & Gamble. The patent states, while luo han guo is very sweet, it has too many interfering aromas, which render it useless for general application. So, the company developed a process for the removal of the interfering aromas.

In this process, the fresh fruit is harvested before it is fully mature, and is then matured in storage so it may be processed precisely when it is mature. The shell and seeds are then removed, and the pulped fruit is made into a fruit concentrate or puree. This is then used in the further production of food. Solvents are used, amongst other things, to remove the interfering aromas.

History
During the Tang dynasty, Guilin was one of the most important Buddhist retreats containing many temples. The fruit was named after the arhats (luóhàn, 羅漢), Buddhist monks who, due to their proper way of life and meditation, achieved enlightenment and liberation.

Luóhàn (羅漢) is a shortened form of āluóhàn (阿羅漢), which is a very old transliteration of the Indian Sanskrit word arhat (prakrit: arahant). In early Buddhist traditions, a monk who becomes enlightened is called an arhat. This is called attaining the "fruition of arhatship," or the "arhat fruit" (Sanskrit: arhattaphala). This was rendered in Chinese as luóhàn guǒ (羅漢果 lit. "arhat fruit"), which later became the Chinese designation for this type of sweet fruit.

According to Chinese history, the fruit was first mentioned in the records of the 13th-century monks who used it. However, plantation space was limited: it existed mainly in the slopes of the Guangxi and Guangdong mountains, and to a lesser degree in Guizhou, Hunan, Jiangxi, and Hainan. This and the difficulty of cultivation meant the fruit did not become part of the Chinese herbal tradition, which depended on more readily available products. This is also the reason no mention of it is found in the traditional guides to herbs.

Western rediscovery in the 20th century
The first report on the herb in English was found in an unpublished manuscript written in 1938 by Professor G. W. Groff and Hoh Hin Cheung. The report stated the fruits were often used as the main ingredients of "cooling drinks", that is, as remedies for hot weather, fever, or other dysfunctions traditionally associated with warmth or heat (i.e. inflammation).

The juice of the fruits was then known to be very sweet.

Interviews have confirmed the fruit only recently gained importance in Chinese history. Nonetheless, a small group of people apparently had mastered its cultivation a long time ago and had accumulated extensive knowledge on growth, pollination, and climatic requirements of the plant.

The fruit was taken to the United States in the early 20th century. Groff mentioned, during a visit to the American ministry of agriculture in 1917, the botanist Frederick Coville showed him a luohanguo fruit bought in a Chinese shop in Washington. Seeds of the fruit which had been bought in Chinese shop in San Francisco were entered into the botanic description of the species in 1941.

The first research into the sweet component of luohan guo is attributed to C. H. Lee, who wrote an English report on it in 1975, and also to Tsunematsu Takemoto, who worked on it the early 1980s in Japan (later Takemoto decided to concentrate on the similar sweet plant, jiaogulan).

The development of luohan guo products in China has continued ever since, focusing in particular on the development of concentrated extracts.