How to Extract and Separate Mogroside？

Luo Han Fruit is the fruit of the Luo Han Guo (Momordica grosvenori Swingler) plant in the Cucurbitaceae family. It is a traditional Chinese medicinal herb unique to China and one of the first dual-purpose medicinal and edible plants announced by the Ministry of Health. Luohan fruit is rich in various nutrients such as vitamin C, vitamin E, fructose, amino acids, trace elements, and also contains various active ingredients such as flavonoids, polysaccharides, sweet glycosides and polyphenols [1].

Mogroside is the main active ingredient in Luohan fruit. It is a triterpene glucoside that is safe for consumption, low in calories and 300 times sweeter than sucrose, making it of wide application value. Mogroside also has a variety of biological activities and pharmacological effects, such as lowering blood sugar, relieving coughs and phlegm, immune regulation, liver protection, antioxidant, anticancer effects, regulating blood lipid metabolism, anti-inflammatory and antibacterial effects, and enhancing immunity [1-3]. Due to the various effects of Mogroside, its extraction, isolation, and development and utilization have aroused great interest among researchers. This paper reviews the extraction, isolation, and detection techniques of Mogroside, with the aim of providing a reference for the comprehensive development and utilization of Mogroside.

1 Extraction and isolation techniques

Mogroside is a triterpene glucoside with high polarity. The extraction solvent mainly uses water, ethanol or a mixture of the two, which are highly polar. Extraction methods include simple solvent extraction, ultrasonic extraction, microwave extraction and flash extraction. After extraction, the main separation methods used include membrane separation technology, macroporous adsorption resin separation technology, semi-preparative high-performance liquid chromatography [4], etc. This article mainly introduces the extraction methods of Mogroside in a classified manner, and the introduction of the separation methods will be mentioned in the extraction methods.

1.1 Simple solvent extraction method

The simple solvent extraction method mainly uses water, ethanol or a mixture of the two as the solvent for extraction. Extraction using water as the solvent is called the decoction method. Fan Yaorong [5] boiled Luo Han Guo for 3 hours, and then used a variety of membranes to separate and concentrate the Luo Han Guo leachate, so that the separation and concentration could be completed in one step, and a high product yield was obtained. Wei Wenjun et al. [6] also extracted Mogroside by boiling in water, and used an orthogonal design to investigate the effects of three factors on the extraction rate: the amount of water added, the boiling time, and the number of boiling times. The best process was found to be adding 18 times the amount of water, boiling three times, and each time for 20 minutes. Nong Yiqing et al. [7] also used water as a solvent for extraction, and then used macroporous adsorption resin for separation. The use of water extraction methods also includes the research of Li Lin et al. [8]: Mogroside was first extracted by hot water extraction, and then separated and purified by macroporous adsorption resin after precipitation and filtration. Two more times of concentration and purification were then carried out, and finally the product was prepared by spray drying. Song Yangcheng [7] used 30% ethanol for extraction, and then used alkaline alumina and macroporous adsorption resin for separation and purification to obtain Mogroside of better quality.

1.2 Ultrasonic extraction method

Ultrasonic waves have a cavitation effect, a mechanical effect and a thermal effect, which greatly promote the extraction of natural products. Ultrasonic extraction has been applied to the extraction of Mogroside. Ma Shaomei et al. [10] used ultrasound to enhance the extraction of Mogroside in ethanol, effectively improving the extraction rate of Mogroside. Li Junsheng et al. [11] focused on the effects of ultrasonic power and frequency on the extraction rate of Mogroside. Zhang Wenqing et al. [12] further established a kinetic model for the ultrasonic extraction of Mogroside.

1.3 Ultrasonic extraction method

Microwave-assisted extraction technology is widely used in the extraction of natural products due to its advantages of high heating efficiency, good selectivity, and fast extraction speed. Zhu Xiaoyun et al. [13] used microwave technology to extract Mogroside, and used the orthogonal test method to examine factors such as the liquid ratio of the Luohanguo feed, microwave output power, extraction time, etc., and compared them with the conventional boiling method. The results showed that the efficiency of the microwave extraction method was significantly better than that of the conventional boiling method, and it is a new extraction method that saves time, energy, and is easy to operate.

1.4 Flash extraction method

Flash extraction is a new technology for extracting traditional Chinese medicine. The principle is to use high-speed mechanical shearing force and ultra-fast dynamic molecular osmosis in the presence of an appropriate solvent to destroy cell tissue, so that the chemical composition inside the tissue cells quickly reaches an internal and external balance, and the extraction is achieved by filtration [14]. Yang et al. [15] used flash extraction to extract Mogroside, and used orthogonal test method to optimize the process. After extraction, XAD macroporous resin was used for separation and purification. Under the optimal conditions of adding 18 times the amount of water to the material, a temperature of 40°C and an extraction time of 7 minutes, the sweet glycoside extraction rate reached 8.77%, and the purity of Mogroside reached more than 92%. Liu Zhao et al. [16] compared the effects of ultrasonic extraction, microwave extraction and flash extraction on Mogroside extraction and found that flash extraction was more effective.

2 Detection technology

Mogroside is regarded as a new generation of functional sweeteners due to its high sweetness, low calories and safety for consumption. However, there is currently no domestic standard for Mogroside, and manufacturers produce according to their own standards. The extraction, separation and purification processes vary widely, resulting in uneven Mogroside product quality and severely limiting the development of the Luohanguo industry. Therefore, the quality standard of Mogroside has also attracted the attention of researchers. Lin Kui et al. [17] reviewed the research progress on the quality and safety standards of Mogroside, including the physicochemical properties of Mogroside such as solubility, stability, and the structure of its active ingredient, sweet glycoside V, as well as toxicity tests, solvents, residues of solvents, additives, and raw materials that may be brought into mogroside during the process. It also gives the control indicators of the mogroside product quality standards of 15 domestic enterprises and the formulation of relevant national or industry standards, and proposes suggestions for the inspection items, concentrations, and testing methods of mogroside quality and safety standards. Among the multiple control indicators for the quality of Mogroside products, the content of its active ingredient Mogroside is the most important indicator. Currently, the methods used to determine the content of Mogroside include high performance liquid chromatography, ultraviolet visible spectrophotometry and enzyme-linked immunosorbent assay [18].

2.1 High performance liquid chromatography (HPLC)

High performance liquid chromatography is a common method for determining the content of mogroside. In the determination process, reverse-phase chromatography is usually used, and acetonitrile-water mixed solvent is mostly used as the mobile phase. The detector is a UV detector, but the detection wavelengths selected by different researchers are slightly different. For a detailed comparison of the methods used by different research groups to determine mogroside by HPLC, see Table 1.

In addition to using HPLC to determine the content of mogroside, researchers have also used its fingerprints for quality control of mogroside products [21].

2.2 Ultraviolet-visible spectrophotometry

UV-Vis spectroscopy is also used in the quality control of Mogroside products or the determination of the content of sweeteners, such as the determination of the content of mogrosides in Luo Han Jiangtang particles [23-24]. There are two methods for determination: one is to directly measure at 203 nm [23]; the other is to color the sample with vanillin-perchloric acid and measure the mogroside at 590 nm [24]. Compared with high performance liquid chromatography, this method is economical, simple, easy to operate, fast and accurate, and can be used as a means of quality control for mogroside products.

3 Conclusion

This paper reviews the extraction and separation and detection techniques for Mogroside. Currently, not many extraction and separation techniques are used, and the application of some techniques is still in its infancy and requires further research. As research on mogroside deepens, more and more efficient extraction and separation techniques will be applied to mogroside research. Mogroside is widely used because of its obvious efficacy, but there is no unified standard in China, resulting in the uneven quality of mogroside products and restricting the development of the mogroside industry. Mogroside quality standards need to be established as soon as possible to regulate the mogroside product market.

The whole body of the Luo Han Guo is full of treasures, but at present, most of the research focuses on Mogroside. There has not been much research on other parts of the Luo Han Guo, and most of the ingredients in the Luo Han Guo have not yet been developed and utilized. The comprehensive utilization and development of the Luo Han Guo will be a very important research direction in the future.

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