What Is the Use of Monk Fruit in the Food Field?

Monk fruit is a traditional Chinese medicinal plant with edible properties. It has been eaten in Guangxi for more than 300 years. It is rich in vitamin C, E, fructose, essential amino acids, trace elements and other nutrients, as well as flavonoids, polysaccharides, glycosides and polyphenols and other active ingredients[1-2]. As a traditional Chinese folk medicine, Luohanguo has the effects of relieving fever, moistening the lungs, relieving cough, relieving phlegm and promoting gastrointestinal function. Japanese scholar Takemoto Tsunematsu found that the part of the monk fruit that is effective against various diseases is the substance in the fruit that is 300 times sweeter than sugar – monk fruit sweetener. The scientific name is “cucurbitane triterpenoid”. It is one of the sweet substances in the triterpenoid family other than sugar. Since the sweetness of monk fruit is a non-sugar component, it can also be consumed by diabetics[3-4].

Japan began importing large quantities of Luo Han Guo from China in the 1990s. In addition to using it as a natural sweetener, Japanese manufacturers have also developed a variety of health foods using Mogroside, such as anti-allergy granules, diet foods, and blood sugar-lowering foods. It is also used as a sweetener in food processing to replace aspartame and sodium saccharin, and is used in the production of food products such as syrup, powdered drinks, chewable tablets, and effervescent tablets [5]. China is the origin and only place where Luo Han Guo is cultivated. It is rich in renewable resources, and the Ministry of Health and the Administration of Traditional Chinese Medicine have included it in the first batch of “species that are both food and medicine” list. It is also widely used as an ideal natural sweetener [6]. Due to the promising application prospects of Luo Han Guo, there have been continuous reports in recent years on the pharmacological effects of Luo Han Guo in the literature. Many new discoveries have been made in terms of antioxidant effects, liver protection, immune enhancement, blood glucose and lipid lowering effects, effects on tolerance to hypoxia, high temperatures and exercise capacity, oral antibacterial effects, and promoting blood circulation and resolving blood stasis, laying a good foundation for the development of new Luo Han Guo products[7]. With the deepening of research on the functional components of Luohanguo, the scope of its application in health foods and food processing is also expanding.

1 Research on the food application of Luo Han Guo

1.1 Luo Han Guo compound drinks

Current data shows that Chinese scientific researchers have made great achievements in Luohanguo drinks. In addition to traditional drinks such as Luohanguo powder and Luohanguo tea, research has been conducted on Luohanguo compound drinks. Yang Hongyuan [8] used fresh Luo Han Guo and kelp as raw materials, extracted the juice and added an appropriate amount of fresh lemon juice and β-cyclodextrin. The mixture was blended, sterilized, vacuum-concentrated, vacuum-dried, crushed, and sieved to produce a Luo Han Guo and kelp solid beverage. Jia Dongying and Deng Jiayun [9] used Luo Han Guo and dates as the main ingredients, supplemented by honey, to make a nutritious beverage with excellent color, taste and aroma. Tan Yining [10] developed a Luo Han Guo walnut compound beverage with the ratio of Luo Han Guo juice:walnut juice=1:2, mixed slurry 40%, honey 0.1%, citric acid 0.1%. Ren Xian'e and Yang Feng et al. [11] used a ratio of 3:1 of Luo Han Guo to sweet tea, a mixture of Luo Han Guo and sweet tea accounting for 50% of the beverage, 2% honey, 0.10% citric acid, and 0.05% salt to prepare a Luo Han Guo sweet tea compound low-sugar beverage. Yu Xin, Chen Yuejiao, et al. [12] prepared a natural Chinese medicinal health drink with a refreshing taste, a sweet and pure aftertaste, and the unique flavors of Hedyotis diffusa and Luo Han Guo, by mixing Hedyotis diffusa extract, Luo Han Guo extract, citric acid, and vitamin C in a ratio of 100 mL:15 mL:0.1 g:0.2 g. Qiu Hua, Chen Yu, et al. [13] used Luo Han Guo and black sesame as the main ingredients to develop a new type of children's health drink that is rich in iron, vegetable protein and functional factors, has a delicate taste, an aromatic smell and high stability.

1.2 Luo Han Guo low sugar drink

In order to meet the demand for low sugar drinks from a wider range of people (especially diabetics), in recent years, scientists have used the high sweetness and low calorie properties of Luo Han Guo to explore the development of low sugar drinks. Huang Zhenguo [14] used Luo Han Guo, wolfberry and licorice, supplemented with beverage additives, to make a low-sugar, cola-type health drink. The drink contains 17 amino acids, trace elements zinc and selenium, and vitamin B2, and has a wide range of health benefits, such as nourishing the yin and lungs, strengthening the spleen and relieving summer heat, and preventing aging and anti-aging. It is especially suitable for obese people and people with diabetes to drink. Liu Guoling, Peng Shanshan, et al. [15] used Luo Han Guo, celery, and chamomile as raw materials to develop a compound health drink with an excellent taste, a unique flavor, and consistent quality. An orthogonal experiment was used to determine the optimal formula of 1% Luo Han Guo, 5% celery, and 1% chamomile. The compound drink was also evaluated for quality. The total acid content of the beverage is 0.003 g/100 mL, the amino nitrogen content is 0.01 mg/100 mL, and the reducing sugar content is 0.001%, which is suitable for people with diabetes.

1.3 Luo Han Guo vinegar drink

In recent years, scholars have also conducted research on Luo Han Guo vinegar drinks. For example, Teng Jianwen [16] used Luo Han Guo and plum vinegar as research objects, combined with honey, and used an orthogonal experimental design method to blend Luo Han Guo vinegar, developing a Luo Han Guo vinegar drink with a good flavor and health benefits.

1.4 Luo Han Guo milk (sour) milk

In addition to Luo Han Guo compound, low-sugar, vinegar drinks, Luo Han Guo is also used for its low-calorie sweetness and its ability to improve the taste of milk. Luo Han Guo milk (acid) milk has been developed, such as Bu Chunwen, Sun Jinfeng, etc. [17] who used Luo Han Guo extract, fermented lactic acid bacteria, cocci, and a thickening and gelling compound stabilizer to replace sucrose to make stirred yogurt. The taste, flavor, and stability all achieved satisfactory results, meeting the needs of consumers who follow a low-sugar, low-calorie diet. Liu Bo [18] used Luo Han Guo and fresh milk as the main ingredients to study the production process of low-sugar milk beverages. Orthogonal experiments were used to screen out the optimal combination and determine the best formula. The formula is: 5 g of monk fruit, 450 mL of fresh milk, 50 g of sucrose, 3.5 g of citric acid, 5 g of CMC, and an appropriate amount of auxiliary material.

1.5 Monk fruit ice cream

Wang Shikuan and Guo Chunxiao[19] used monk fruit juice as the main raw material and studied the production process of monk fruit fermented milk ice cream using orthogonal experiments. The results showed that the optimal formula for Luohanguo fermented milk ice cream was 25% Luohanguo juice, 0.4% compound stabilizer, 14% erythritol, and 30% fermented milk, which resulted in an ice cream product with high nutritional value and a unique flavor that combined the dual characteristics of yogurt and ice cream.

1.6 Luohanguo fermented wine

In the development of Luohanguo wine, Yue Zhe [20] used Luohanguo infusion to add sugars (can be sucrose, glucose, fructose, malt) and a certain amount of bran (starch) for fermentation. The fermented filtrate was heated and sterilized at 63 °C, then allowed to stand and age for six months in an airtight container. The finished Luohanguo fermented wine is then filtered through activated carbon, tinted and flavored. The product is light yellow in color, with an alcohol content of 12–16%, a pH of 3.4–3.6, an acidity of 1%–2%, and a suitable sweetness. It has a unique sweet flavor of Luohanguo, is mellow and full-bodied, and has a good flavor. It also has medical effects such as relieving coughs, calming asthma, and lowering cholesterol. It has no pungent or stimulating taste and is suitable for people of all ages.

1.7 Luo Han Guo single crystal rock sugar

Luo Han Guo is a traditional Chinese food supplement that enjoys a high reputation among Chinese people at home and abroad. Zeng Aiyuan [21] used water to extract the active ingredients of Luo Han Guo, which were forced to adsorb on the surface of white sugar crystals. In a certain supersaturated sugar solution, the crystals were grown in a rocking crystallizer to form crystals similar to amber, with a polyhedral shape, uniform crystal columns, moderately sweet, highly moisture-resistant, non-polluting, and can be eaten directly as candy or boiled into a high-grade tonic. It is a sandwich-type single crystal sugar with the color and aroma of Luo Han Guo.

1.8 Luo Han Guo bread

Ma Yanguo and Chen Zhaolang [22] used a secondary fermentation method to sandwich in Luo Han Guo extract to study Luo Han Guo bread. The product has a good taste, a loose internal structure, a strong sense of layering, and a strong Luo Han Guo flavor. It uses about 80% less sucrose than bread without Luo Han Guo extract, which reduces the degree of damage to the flavor substances.

1.9 Luo Han Guo pickles

Lin Yanwen [23] used stuffed mustard and carrots as raw materials, added Luo Han Guo water extract (3:2 ratio of vegetable liquid), and used an orthogonal experimental method to make kimchi. Combining the number of lactic acid bacteria in the kimchi and the time to maintain a high bacterial count, the optimal process conditions were determined to be: 4% Luo Han Guo water extract, 4% salt concentration, 1% sugar concentration, 3% inoculum, 30°C fermentation temperature, and fermentation time 5d. Based on these conditions, a new type of pickled health food with the effects of quenching summer thirst, clearing away heat and detoxifying, relieving cough and resolving phlegm has been developed.

1.10 Luo Han Guo low glycemic index nutritional powder

Low glycemic index nutritional foods are a type of food that combines nutrition and health care, and are suitable for people with diabetes and obesity. They are widely used in international food research and development. He Weiping, Zhu Xiaoyun, et al. [24] studied a low-GI nutritional powder made from Luo Han Guo, and found that the GI values were 53.30 for the middle-aged and elderly type, 54.45 for the female type, and 53.67 for the children's type. Within 2 hours after a meal, the areas under the blood glucose curves of the nutritional powders of each type were compared with those of glucose, and it was found that P<0.01, which indicates a very significant difference. In addition, the time of peak value for each group was significantly delayed, and the difference between the highest and lowest blood glucose values is also significantly reduced. The main nutrient content of the monk fruit nutrition powder is similar to that of milk powder, but the calorie value and carbohydrates are lower than those of whole milk powder, and the dietary fibre (water-soluble and insoluble) content is relatively high. In addition, monk fruit also contains a variety of nutritionally active ingredients, making it both a low-glycemic-index food and a health product that can regulate blood sugar.

1.11 Monk fruit fat-lowering and weight-loss food

The sweetness of Luo Han Guo is not derived from sugars, but it is about 300 times sweeter than sucrose, so it can be used as a dietary sweetener to completely eliminate sugar intake. As long as sugar intake is controlled, subcutaneous fat assimilation can be inhibited, and the removal of subcutaneous fat through promotion of catabolism can lead to weight loss. Zhu Xiaoyun, He Weiping, et al. [25] conducted research on Luo Han Guo fat-lowering and weight-loss food, and used male rats as experimental subjects for fat-lowering and weight-loss experiments. The results showed that after 28 days of eating the same amount of Luo Han Guo fat-reducing and weight-loss food, the Luo Han Guo fat-reducing and weight-loss product caused a 11.9% weight loss compared to the control group, a 35.7% reduction in body fat, a 38.9% reduction in serum triglycerides, a 21.2% reduction in total cholesterol, and a 37.8% reduction in low-density lipoprotein cholesterol.

2 Problems in the development of Luo Han Guo food products

2.1 Taste issues with Luo Han Guo products

Currently, there are certain taste issues with Luo Han Guo products developed in the laboratory or launched on the market. If a product contains a large amount of Luo Han Guo, the sweetness lingers in the mouth for too long, which makes the mouth feel heavy and uncomfortable. If dried Luo Han Guo is used in the production, the product has a burnt, bitter Chinese medicinal taste. If a drink is produced directly using a fresh Luo Han Guo water extract, it has a strong grassy, green taste. Due to improper processing of the taste of Luo Han Guo products, people often consume Luo Han Guo products with the perception of medicine. Therefore, the key to improving the application of Luo Han Guo products is to develop the taste of Luo Han Guo food, avoid the burnt and bitter Chinese medicinal taste of Luo Han Guo, shorten the sweetness retention time in the mouth, and eliminate the grassy taste of fresh fruit.

2.2 Application problems of the nutritional and functional ingredients of Luo Han Guo

Due to the high sweetness of Luo Han Guo, in food applications, attention is often only focused on the use of the sweet taste of Luo Han Guo, while the value of using the other rich nutritional and functional ingredients is overlooked. Therefore, in the future research and development process, efforts should also be made to explore the use of nutritional and functional ingredients in the research process, and to produce Luo Han Guo foods that integrate health, nutrition and wellness.

2.3 Insufficient research and development

Although the majority of scientific and technical workers have conducted extensive basic research and product development on the food applications of Luo Han Guo, there is still a lack of varieties of Luo Han Guo products on the consumer market in China. Coupled with the influence of regional consumption habits, the consumption of Luo Han Guo products, except for individual varieties such as Luo Han Guo tea (powder), is still very low. Therefore, how to transform scientific and technological achievements into actual economic benefits in food applications, thereby promoting the development of the Luo Han Guo planting and processing industry, will be an important topic for close collaboration between scientific researchers and producers.

3 Research outlook

The main food application of Luo Han Guo in China is to use its high sweetness to replace some other sweeteners in the production of various foods. With the research in recent years on the antioxidant effect of Luo Han Guo in scavenging free radicals, its effect in regulating blood sugar, its immunomodulatory effect and other medical functions, its functional role has attracted increasing attention. The problems with the current research on the food applications of Luo Han Guo can be solved in the following ways: firstly, a compound seasoning method can be used to reduce the aftertaste of Luo Han Guo in the mouth and throat, and research can be carried out on Luo Han Guo foods that are sweet but not greasy and refreshing; secondly, the functional properties of Luo Han Guo can be used to develop sugar-free sweet drinks[4], anti-diabetic foods[26-27], anti-caries food for children [28], anti-aging food [29], constipation-preventing food [30], lipid-lowering and weight-loss food [25], and low-glycemic-index food [24], etc., and the application of Luo Han Guo has developed from traditional foods to new functional health foods. We believe that with the continuous deepening of basic research and product development, coupled with people's increasing awareness of their own health, this ancient and unique dual-purpose medicinal and food resource will definitely play an even more important role in people's daily lives.

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