Luo Han Guo (Siraitia Grosvenorii): A source of zero calorie sugar substitute

Fresh Luo Han Guo on the vine (Siraitia grosvenorii)
Image Source: Stauberusa.com

Binomial Name

Siraitia grosvenorii (Swingle) C. Jeffrey ex A.M. Lu & Zhi Y. Zhange(Cucurbitaceae)

Synonyms

Momordica grosenorii (Swingle)

Siraitia siamensis (Craib) C. Jeffrey ex S. Q. Zhong & D. Fang

Thladiantha grosvenorii (Swingle) C. Jeffrey

Common Names

A Luo Han, Arhat fruit, Buddha fruit, Big Fellow’s Fruit, Chang Shou Guo, Fructus Momordicae, La Han Qua (vietnamese), Lo Han Guo, Lo Han Kuo, Longevity Fruit, Luo Han Guo, Momordica Fruit, Momordicae Grosvenori Fructus, Monk Fruit, Rakanka, Swingle Fruit, Na Han Gwa, Rakanka (Japanese), nahan’gwa (Korean)

Botanical Description

Figure 1. Drawing of S. grosvenorii: 1. Stem; 2. Leaf; 3. Flower; 4. Fruit (Li et al., 2014)

Siraitia grosvenorii, a member of the Cucurbitaceae (gourd) family,is an herbaceous perennial vine (Fig. 1) that grows from 2 to 5 meters by clinging tendrils. The plant has sturdy stems and branches, as well as enlarged and spindle-shaped roots. The petioles are 3-10 cm long; the narrow, thin and heart-shaped leaf blades are 10-20 cm long and 3-12 cm broad (Swingle, 1941).

S. grosvenorii is a dioecious plant that flowers in early summer. The male inflorescences are axillary with 5 to 7 of them arranged in racemes; female inflorescences are solitary or cluster (2 to 5) in leaf axils. The plant is best known for its fruit, commonly known as monk fruit or Luo Han Guo. With a diameter of 5 to 7 centimetres, the monk fruit is small in size and has a round to oval shape. The smooth rind is dark green and firm when fresh (sometimes covered in fine hair) but turns brown and brittle when dried. Underneath the thin shell is an edible pulp that is packed with elongated, round seeds. The inside of the fruit transforms into a light fibrous mass when dried and is intensely sweet with an aromatic odour and flavour (Swingle, 1941).

History

The formal Chinese name of the fruitis Luo Han Guo (Chinese: 罗汉果), which was named in honour of the arhats, a group the Buddhist monks who were among the first to discover it back in the 13th century. The fruit is reputed to aid longevity and associated with general wellbeing. It has long been consumed by local people as a food ingredient and in traditional medicine (Dharmananda, 2004). 

The earliest English report on S. grosvenorii was written by Dr. Groff and Dr. Cheung in 1938. It states that Luo Han Guo was commonly used in the making of “cooling drinks”, a household remedy to counter fever, hot weather, and conditions associated with inflammation (Swingle, 1941). 

Although the fruit was introduced to the United States in the early 20th century, it did not gain reputation until after 1975 when serious research began into its potential as a sweetener (Croom Jr, 1999; Dharmananda, 2004). Since then, Luo Han Guo products have seen a steady rise in popularity with focus on the extraction of its constituents (Dharmananda, 2004). 

Origin and Distribution

S. grosvenorii is native to southern China; it primarily grows in the mountains of Guilin (a city of the province, Guangxi), as well as in Guangdong, Guizhou, Hunan, Jiangxi, and Hainan island (Swingle, 1941). The plant is rare in the wild and the earliest cultivation record dates back to 1813 (Dharmananda, 2004). Before 1965, Luo Han Guo was consumed only to a limited extent by the locals with an annual production of less than 1 million fruits. As the fruit gained more popularity due to its potential as a source of low-calorie sweetener, its market has grown significantly. Nowadays, the annual production of fruits from Guilin has increased to 300-400 million, accounting for 90% of the world’s supply (Baines and Seal, 2012; Ji, 2016). Most plantations are in the Yongfu County of Guilin, with the Longjiang (Dragon River) Town being the “home of Chinese Luo Han Guo fruit”. The companies that are specialized in the production of Luo Han Guo extracts and their products are also located in this area (Ji, 2016). 

Over the years, the fruit has travelled to more than 20 countries in the world, including the United States and Southeast Asia. However, most of the world is still unaware of Luo Han Guo due to limited growing area and difficulty in cultivation (Baines and Seal, 2012). 

Habitat

S. grosvenorii is typically found in forests, thickets, riversides and on the mountain slope. The mountainous regions (at an altitude of 600—700 meters) in Guilin, China, are among the best habitats for the plants (Swingle, 1941) (Fig. 3). The steep mountains are frequently surrounded by mists, providing shade to the plants and protecting them from excessive sun exposure. Nonetheless, the climate in Southern China is usually warm and rainy, which further contributes to the growth of the plants (Lu and Zhang, 1984; Dharmananda, 2004).

Cultivation Practice

Figure 3. The growing location and condition of Luo Han Guo
Image Source: Lankanto.com

S. grosvenorii is difficult to cultivate and only grows in a specific climatic zone.  They have to be planted on the slopes of cool, tropical, or subtropical mountains with relatively high humidity (≥ 75%). The optimal growing conditions for S. grosvenorii require an altitude of 150 meters – 800 meters, a temperature of 15 ⁰C to 30 ⁰C (59 ⁰F to 86 ⁰F), annual rainfall of 1500 mm – 2000 mm, and annual sunlight of 1100 h – 1600 h. S. grosvenorii loves light but not for long periods, preferring only 6 to 7 hours of sunlight per day. Thus, plants should be surrounded by shadows of other trees or mountain slopes to protect them from excessive sunlight (Bai, et al., 2009). Well-drained, loamy soil is best suited for cultivation (Lim, 2012). Since it is a cross-pollinated species, pollinators are required. With nothing known about natural pollinators, hand pollination is often resorted to in commercial cultivation (Thakur et al., 2021). The growth cycle of S. grosvenorii is slow and divided into four stages: seedling (March to April), flowering (May to July), fruit set (July to September) and withering (past November) (Baines and Seal, 2012).

In Guilin, the elevation of the plantation sites and steepness of slopes provides natural protection from flood damage and access to unpolluted water. There are trellises across the field to support the vigorous climbing of the vines. Each plant is carefully tended and maintained to ensure quality yields. To prevent bugs from destroying the fruits, natural techniques such as netting and bottle traps are used by the farmers (Ji, 2016).

For a sustainable tradition of field cycling and to ensure the soil stays fertile for optimal fruit growth, the plantation sites are rotated every 5 years. This means that trees are planted after 3 years to grow alongside S. grosvenorii for the final 2 years. Following that, poles and netting are removed so that the trees can grow into a forest, allowing the ecosystem to restore balance (Baines and Seal, 2012).

Ethnobotanical Uses

Medicine:

S. grosvenorii is best known for its fruit, which is reputed to aid longevity and traditionally used as an herbal medicine to eliminate pharyngitis (sore throat), phlegm, as well as an anti-tussive (coughs) remedy in China (Gong et al., 2019). According to the Encyclopedia of Traditional Chinese Medicine, the use of dried fruits at a rate of 10 to 15 g or as a whole fruit boiled in water every day, is beneficial for respiratory problems and bowel movements (Croom Jr, 1999). The Chinese book Fruit as Medicine alsoreported the uses of fruits for heatstroke with thirst, acute and chronic throat inflammation, aphonia, chronic cough, constipation in the aged, and as a sugar substitute for diabetics(Croom Jr, 1999).

Food:

Figure 4. The structure of Mogroside V

The fruit of S. grosvenorii is considered a functional food, because it contains many nutritious compounds, such as mogrosides, linoleic acid, vitamin C, and other unsaturated fatty acids. The sweetness of Luo Han Guo arises mainly from Mogroside V (Fig. 4), the most abundant component that makes up approximately 1% of the pulp of the fruit, making it 300 times sweeter than sucrose (Li et al., 2014). In the 1900s, the China Food and Drug Administration (CFDA) approved the use of S. grosvenorii as a sweetener in foods. Later in 1996, it was approved as a sweetener substitute in health foods for obesity and diabetes patients. As a new low-calorie, non-sugar sweetener, S. grosvenorii can be consumed in the form of juice or as an additive or used to prepare sugar-free, low calorie foods (Gong et al., 2019).

Cosmetic:

Some components of Luo Han Guo are authorized for use in cosmetic products by the European Commission Health and Consumers Directorate General. The powder obtained from the dried, ground fruit of S. grosvenorii is listed as an abrasive, which can be used in products like body scrubs or aids in tooth cleaning or improves gloss. The juice from the fruit is listed as a humectant, which helps to retain moisture. Lastly, the extract of the fruit is listed as an antioxidant and skin-conditioning substance. Currently, use of S. grosvenorii as a cosmetic ingredient is limited. More research efforts are required to investigate the potential application of the plant in cosmetic products (Engels and Brinckmann, 2014).

Descriptions of Plant Products

Commercially, Luo Han Guo is available as dried fruits (Fig. 5) and can be used as whole, powered or in block form depending on the needs of the users. Below are some popular applications of the plant.

Dried Fruit

Figure 5. Dried Luo Han Guo
Image Source: Solomon, 2018

The general process of preparation from the dried fruit is to boil or simmer in water and drink as an herb tea or soup (Croom Jr, 1999). Some applications of Luo Han Guo in Traditional Chinese Medicine include the following (Dharmananda, 2004):

  1. For throat inflammation, simmer half of a fruit with 3-5 seeds of sterculia in the water and swallow very slowly.
  2. For chronic cough,simmer a whole Luo Han Guo with water and drink the liquid, twice each day.
  3. For constipation, extract the seeds and juicy portion of 2 pieces of fruit, and simmer with water; drink before bed.
  4. Patients with diabetes can boil the fruit into a thick concentrate and add to it to food as a substitute for sugar.
  5. For heatstroke, take 1 piece of Luo Han Guo and break it apart before boiling with water; consume the liquid only.

Medicinal Beverages

Figure 6. Instant Luo Han Guo medicinal beverages in the form of (a) cubes and (b) granules
Image source: Michiyorynne.com

Another popular use for the fruit is in medical beverages. Luo Han Guo Chong Ji, is an instantly dissolvable extract. The product is available in the form of cubes (Fig. 6 a) or granules (Fig 6 (b)). These are usually dissolved in hot water and consumed as a medicinal aid for colds and digestions (Dharmananda, 2004; Ji, 2016).

Herb Tea

Figure 7. Luo Han Guo tea is produced with herbs like chrysanthemum (left) and artichoke (right)
Image Sources: Chinaglobalmall.com; Alibaba.com

Luo Han Guo is also commercially prepared as tea, often in combination with other herbs such as chrysanthemum or artichoke (Fig. 7) (Ji, 2016). Other herbs such as ginkgo, asparagus and Scutellaria are also mixed with Luo Han Guo to get tea (Dharmananda, 2004).

Sugar Substitute

Another popular use for the fruit is in medical beverages. Luo Han Guo Chong Ji, is an instantly dissolvable extract. The product is available in the form of cubes (Fig. 6 a) or granules (Fig 6 (b)). These are usually dissolved in hot water and consumed as a medicinal aid for colds and digestions (Dharmananda, 2004; Ji, 2016).

Figure 8. Lakanto® Classic Monkfruit Sweetener
Image Source: Lakanto.com

There is a growing demand for healthy, natural low-calorie sweeteners driven by the rising awareness of the public regarding negative health effects (i.e., obesity and diabetes) associated with excessive sugar intake. While Luo Han Guo has known to be beneficial for diabetic patients for decades in China, it has only become more recognized in North America recently due to the increased practice of keto diet. It is a popular sugar substitute for the keto diet because it has no carbs or calories (Mordor Intelligence, 2021). Moreover, it has been associated with diabetes for decades because it doesn’t increase blood sugar levels (Croom Jr, 1999).

Conservation Status

Due to economic development and deforestation, the natural ecosystem of wild S. grosvenorii has been severely affected. As a result, the wild plants started to perish because they were unable to adapt to their new living condition (Ning, 2019).

The lack of protection awareness has resulted in further damage of the growing environment of wild S. grosvenorii. Wild Luo Han Guo has a small yield but high in sweetness, making its market value higher than the cultivated ones. Therefore, local farmers are racing against each other to collect them in the mature season. The neglect and trampling of the farmers throughout this process results in the damage of tubers, which then affects the germination of wild S. grosvenorii in the following year (Ning, 2019).

There has been a degradation of the farmed S. grosvenorii due to the careless practice of cross-pollination. As a result, some wild sources of S. grosvenorii were used to revive the quality of the farmed ones. With the decline of the wild sourcesthe quality of cultivated fruit will surely suffer. While the current conservation status of the wild plant is still under investigation, a protection plan is needed before further damage is done (Ning, 2019).

Harvesting and Processing Techniques

Between September to November, Luo Han Guo turns from pale green to deep green, an indication of ripeness and that they are ready to be harvested (Ji, 2016).

Traditional Processing

Figure 9. Post-harvest processing of Luo Han Guo
Credit: Ji, 2016

Traditionally, the fruits are hand-picked and fire-dried—a process that preserves the fruit since fresh fruits are hard to store. Once the fruits are dried, they appear to be brown and are sold in Chinese herb stores as a medicinal ingredient of Traditional Chinese Medicine (Engels and Brinckmann, 2014). While the drying process eliminates the concern of preservation and removes most of the unattractive flavours from the fresh fruit, it also creates a bitter and astringent flavour. This restricts the consumption of the dried fruits through the preparation of tea or soup, to which sugar or honey is sometimes added (Dharmananda, 2004; Fischer et al., 1995).

The Procter & Gamble Process

Figure 10. The modern practice of Luo Han Guo extraction
Image Source: Lakanto.com

Although Luo Han Guo is sweet in nature, it has many interfering aromas (i.e., unattractive vegetable flavour), limiting its palatability. Procter & Gamble Company developed a technique that produces the product without any after-taste which became the first step in the development of the sugar substitute from Luo Han Guo (Fischer et al., 1995).

In this method, fresh fruits are harvested before they reach full maturity, then they are matured in storage until they are ready to be processed. The process requires the removal of seeds and skin of the fruit before they are mechanically crushed to collect the juice. The fruit extract, or juice, contains zero calories per serving, which is further used in the production of sweeteners (Fischer et al., 1995; Baines and Seal, 2012).  

Market Status

The dried fruit used in TCM formulations or as starting material for the manufacture of extracts is relatively inexpensive at this time. During the 2013 harvest, from late August to early October, the lowest average market price was at ¥0.85 /kg (Approximately $0.16/kg in CAD), and the highest average market price was at ¥1.49 /kg (Approximately $0.29/kg in CAD). The prices remained stable at around ¥1.00 /kg (Approximately $0.19/kg in CAD) in summer 2014 (Engels and Brinckmann, 2014)

The market for Luo Han Guo appears to be sufficient for the existing global demand for Traditional Chinese Medicine formulas and products. However, with a growing approval of fruit extracts for uses such as enhancing flavour and/or sweetening in more countries, there will be an increase in demand

Acknowledgment

This was an assignment written for Botany*2000 Plants, Biology and People at the University of Guelph. I wish to give a grateful acknowledgment to Professor Jayasankar Subramanian (University of Guelph) for the suggestion and encouragement, editing this paper and recommending it to Spiritual Botany. I also thank Dr. Praveen Saxena, the Editor of Spiritual Botany for the opportunity to have this paper published. 

About the Author

Yan (Leanne) Li graduated from the University of Guelph with a major in Biomedical Science and a minor in Psychology in 2021 summer. Her interest in health communication and promotion made her to pursue a Master of Science in Population Medicine (Public Health) at University of Guelph. With the knowledge and skills she is going to gain from her graduate studies she wants to contribute to the health of the community.


References

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