Study on the Active Ingredient in Luo Han Guo Extract

Luo Han fruit is the dried fruit of the Momordica grosvenorii Swingle plant in the Cucurbitaceae family [1]. The currently cultivated varieties are Longtan fruit, Lajiang fruit, Dongguahan, and Qingpi fruit [2]. Luohan fruit is cool in nature, sweet in taste, non-toxic, and enters the lung and large intestine meridians. It is one of the common ingredients used to make herbal tea in southern China. According to Liu Jing [3], Luo Han Guo contains active ingredients such as sweeteners, polyphenols, total sugars, polysaccharides, amino acids, alkaloids, etc., and has physiological activities such as relieving coughs, relieving phlegm, relieving spasms, anti-oxidation, protecting the liver, enhancing immunity, inhibiting bacteria, and anti-cancer. The physiological active ingredients, health-promoting functions, and extraction and determination of the main physiological active ingredients of Luo Han Guo are summarized as follows. 

1 Physiological active ingredients

1.1 Triterpenoids

Triterpenoids are substances composed of several isoprene units connected end to end after the hydroxyl groups have been removed. They are found in legumes, araliaceae, campanulaceae, polygonaceae, cucurbitaceae and other plants. Since Lee isolated the triterpenoid sweetener from the fruit of the monk fruit in 1975, eleven types of cucurbitane triterpenoid glycosides have been isolated and identified from the fruit of Luo Han Guo. Luo Han Guo glycoside V, which accounts for about 0.5% of the dried fruit, is the main component of the dried fruit of Luo Han Guo [4].

1.2 Flavonoids

Flavonoids refer to compounds with a 2-phenylchromenone nucleus, which are considered to have a nutritional function in biological reactions and were once called “vitamin B”. The flavonoids in Luo Han Guo include Luo Han Guo Flavone, Kaempferol-3,7-O-α-L-rhamnoside [5], Kaempferol 7-O-α-L-rhamnoside, Kaempferol, etc. [6]. According to literature [7], the female and male flowers of Luohanguo contain flavonoid glycosides and kaempferol glycosides, with contents of 1.05% and 0.49%, respectively, and no quercetin.

1.3 Lignans

Lignans are a class of natural compounds formed by the polymerisation of two molecules of a phenylpropanoid derivative (i.e. C6-C3 monomers) and are a type of phytoestrogen. Liao Riquan et al. isolated magnolol from Luohanguo, which, in addition to having strong activity in scavenging oxygen free radicals, also has a protective effect against cerebral ischaemia and significantly suppresses the withdrawal response to morphine in rats [8-9]. Li Jun et al. isolated vanillic acid from the chloroform extract obtained by extracting with 75% ethanol, which can be used in the synthesis of spices or medicines [10].

1.4 Furan compounds

Furan compounds are heterocyclic compounds used as intermediates in the synthesis of furan drugs [11]. Liao Riquan et al. isolated bis[5-formylfurfuryl] ether and 5-hydroxymethylfurfuroic acid from Luo Han Guo, among which bis[5-formylfurfuryl] ether not only has an inhibitory effect on fungi, but also has antiviral and antioxidant effects [12].

1.5 Carbohydrate compounds

Polysaccharides are widely found in plant, animal and microbial tissues, and have a variety of important functions. According to literature [13] and [14], the monosaccharide residues in the monomeric polysaccharide SGPS1 of Luo Han Guo exist in the form of pyran and furan rings, and its monosaccharide composition is glucose, galactose, xylose, arabinose, rhamnose and glucuronic acid. The monosaccharide residues in SGPS2 exist in the form of α-pyran rings, and its monosaccharide composition is rhamnose and glucuronic acid.

1.6 Fatty acid compounds

Luohanguo seed oil contains linoleic acid, oleic acid, palmitic acid, stearic acid, palmitoleic acid, myristic acid, lauric acid, and decanoic acid [15]. According to literature [16], Luohanguo seed oil contains nine fatty acids, the main components of which are linoleic acid (47.2%) and linolenic acid (24.53%). Unsaturated fatty acids account for 82.56%, and polyunsaturated fatty acids account for 71.73% of the total fatty acid composition.

2 Pharmacological effects of Luo han guo

2.1 Antioxidant effect

Research by Deng Qili and others has shown that the flavonoids in the leaves of the monk fruit can improve the body's antioxidant capacity and delay the onset of exercise fatigue. The mechanism is that after taking monk fruit leaf flavonoids, the model rats studied were able to improve their quadriceps Na + / K + -ATPase, Ca2 + / Mn2 + -ATPase and total ATPase capacity after swimming until exhaustion, thereby maintaining the osmotic pressure and transmembrane potential balance inside and outside the cell membrane, maintaining the homeostasis of Ca2 + / Mn2 + inside and outside the cell, and maintaining a relatively high energy supply [17].

2.2 Antibacterial effect

Lin Yanwen et al. used the water decoction method, ethanol extraction method, and water addition grinding method to prepare the raw solution of Luo Han Guo, studied the effects of the three types of raw Luo Han Guo solution on the growth and preservation of the vitality of Lactobacillus plantarum, Bifidobacterium longum and Streptococcus thermophilus, which are closely related to humans [18]. The results showed that the raw Luo Han Guo solution prepared by the water decoction method had the best growth-promoting effect on the three types of lactic acid bacteria, followed by the ethanol extraction method, and the worst was the water grinding method [19].

2.3 Lipid-lowering and blood-sugar-lowering effects

Zhao Yan's research results show that Luo Han Guo concentrated juice and Luo Han Guo sweeteners have lipid-lowering effects, such as lowering total serum cholesterol, lowering triglycerides, and raising high-density lipoprotein cholesterol [20-21].

2.4 Immune-enhancing and anti-fatigue effects

Other studies have shown that Luo Han Guo sweeteners can increase the percentage of peripheral blood acid-acetate naphthylamide positive lymphocytes and the rate of E rosette formation [22]; it can significantly enhance the cellular immune function of CTX immunosuppressed mice, suggesting that Luo Han Guo sweeteners have a regulatory effect on mouse immune function, and the specific mechanism of action needs to be studied [23-25].

3 Extraction and determination of triterpenoid compounds in Luo Han Guo

The main chemical component in the fruit of Luo Han Guo is Mogroside V. Most of these substances are strong sweeteners and slightly sweet substances. Ripe Luo Han Guo is rich in Luo Han Guo sweeteners, of which Luo Han Guo glycoside V is the main sweet component in the fruit, with a high content of sweetness (256 to 344 times the sweetness of sucrose). Luohan fruit glycoside is a triterpene glycoside, and the extraction and determination methods of triterpenoids in Luohan fruit are summarized as follows.

3.1 Extraction method

In terms of the extraction rate, the microwave method and the hot reflux method should be selected. From the perspective of extraction equipment and instruments, the solvent method or the solvent application extraction method should be selected. From the perspective of environmental protection and energy conservation, flash extraction technology and ultrasonic enhancement should be selected.

3.2 Determination method

The sensitivity of the Fourier transform infrared spectroscopy and high performance liquid chromatography methods for the determination of triterpenoids in Luohanguo is relatively high, while the vanillin perchlorate colorimetry does not require special instruments and equipment, and the thin layer scanning method is faster. The method of measurement can be selected according to actual conditions and requirements.

4 Conclusion

In recent years, there has been a lot of research on Luo Han Guo at home and abroad, mainly focusing on the research of the non-sugar sweet substances cucurbitane triterpenoid compounds. Further research is needed on other issues related to Luo Han Guo, such as the fact that Luo Han Guo flavonoids can improve the activity of the rat quadriceps femoris Na + / K + -ATPase, Ca2 + / Mg2 + -ATPase and total ATPase after swimming to exhaustion, but the mechanism needs to be studied in depth. At present, the research on the biological activity of Luo Han Guo extract is not in-depth enough, and there is a lack of reports on research at the cellular and molecular levels. This will be the focus of future research. For example, Luo Han Guo sweet glycosides have an inhibitory effect on the proliferation of hepatic stellate cells HSC-T6 and liver fibrosis, but the mechanism of action needs to be further explored.

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