Is Stevia Good for Health?

1 Stevia overview and characteristics of stevia

Stevia is native to the Andes Mountains at the border of Paraguay and Brazil in South America. It is a perennial herb that has been used for hundreds of years by the native people of the area as a natural, green plant beverage with a sweet taste and health benefits. It was successfully introduced and cultivated in China in the 1970s, and is now widely cultivated or introduced in Jiangsu, Anhui, Jiangxi, Shandong, Heilongjiang, Gansu, Xinjiang, Hunan, Yunnan, Hebei, Shaanxi and other places. With the expansion of its industrial scale, China has now become the world's largest producer and exporter of stevia [1]. In addition to stevioside, the dried leaves of Stevia rebaudiana Bertoni contain non-sugar components such as protein, fat, cellulose, phenolic acids, flavonoids, vitamins, and trace elements [2].

The residue after stevioside is extracted in industry contains a large amount of cellulose, nitrogen-free leachate, crude protein, etc. [3]. The glycosides in stevia belong to the terpene compound class. More than ten such ingredients have been isolated from stevia, and the extraction and separation technology is quite mature [4].

These include the recently much-discussed rebaudioside D (RD) and rebaudioside M (RM), these glycosides all contain the same aglycone steviol, which has different numbers of glucose or rhamnose groups attached to the C19 and C13 positions, making the sweetness and taste quality very different. The two main types are stevioside and rebaudioside A (RA). RA is a sweeter and more popular sweetener than stevioside. It is 300 times sweeter than sucrose, stable to acids, alkalis and heat, and does not deteriorate during long-term storage. It does not cause browning when added to food will not undergo browning after heat treatment, making it an ideal replacement for traditional sweeteners and a green health product. The general structural formula and some components of stevioside are shown in Figure 1 and Table 1 [5], respectively.

Stevioside is a sweetener approved for use by the Chinese Ministry of Health. Because of its naturally low caloric value and very similar taste to sucrose, it is the third natural sweetener with great development value and health benefits after cane sugar and beet sugar. It has been internationally hailed as the “world's third sugar source”. The production and research of stevia as a sweetener, new health products and drug development is booming [6-8].

2 The medicinal value of stevia and stevioside

Stevia has been used as a sweetener abroad for many years, and its acreage has increased year by year. It is cultivated in many countries and regions such as Paraguay, Malaysia, the United States, Canada and Europe. In addition to replacing some traditional sweeteners such as sucrose and saccharin, stevia also has remarkable medicinal functions.

2.1 The antihypertensive and hypoglycemic functions of stevia

Stevia can be used to help treat high blood pressure and high blood sugar. Its mechanism of action is similar to that of western medicine calcium channel blockers [9]. People with high blood pressure can brew stevia leaves and drink it as a tea, as a health drink to help lower blood pressure. Studies have found that the blood pressure lowering effect of stevia is similar to that of existing antihypertensive drugs, but it does not have the side effects of calcium channel blockers, diuretics, angiotensin converting enzyme inhibitors and other antihypertensive drugs, such as palpitations, low blood potassium and cough. Dr. Calaghan, an expert in pharmacology, believes that there is no risk in using stevia even in cases of low blood pressure. Stevioside lowers blood sugar by promoting the formation of glycogen and the activation of related receptors [10-36]. Stevia only exerts its hypoglycemic effect in the presence of high blood sugar, so for healthy people, consuming stevioside is safe [11-12].

2.2 The antibacterial and anti-inflammatory properties of stevia

Stevioside has anti-tuberculosis effects, and its acylhydrazones have better therapeutic effects than ordinary anti-tuberculosis drugs [13]. Stevioside can also be used as an intermediate to further derivatize into other substances with better physiological activity. For example, stevioside esters containing quaternary ammonium salts have good antibacterial properties [14], and the diamino compound of stevioside has a diastereoisomer that is superior to penicillin in its ability to inhibit the growth of Bacillus subtilis [15]. Stevioside is an isomer of steviol glycoside, which has anti-fatigue and immune-enhancing effects [16-18]. Steviol is the aglycone of steviol glycosides, which has physiological activities such as anti-bacterial, anti-inflammatory and anti-tumor [19].

2.3 Medicinal functions of steviolic acid compounds

Stevia contains phenolic acid components (chlorogenic acid is one of them), and foreign literature reports the content to be 1.29% [20]. The content of total caffeoylquinic acids in stevia measured by our research group reached 3.28% (some varieties are even higher), of which the content of di-caffeoylquinic acid is 2.65%, much higher than the total caffeoylquinic acid content in tobacco (0.54%) [21] and the total caffeoylquinic acid content in Jerusalem artichoke (0.16%) [22]. Caffeoylquinic acid substances have a variety of physiological and pharmacological functions, such as antioxidant activity, antibacterial, antiviral effects, enzyme inhibition [23-24], hepatocyte protection [25], inhibition of mutation and antitumor effects [26-27], etc. In the United States, Brenda McDougall and others found that 1,5-di-O-caffeoylquinic acid and some other di-caffeoylquinic acids have a good inhibitory effect on HIV-1, and that the therapeutic dose is much lower than the toxic dose [28].

3 Stevia sugar as a sweetener and modification

Through the conversion action of biological enzymes, the introduction of new glycans or the conversion of glycans in the glycogen part of stevioside can improve the sweetness of stevioside and retain the low-calorie properties of stevioside. Enzyme-based transformations mainly include the cyclodextrin glucanotransferase method, the fructofuranosyltransferase method, the glucosidase method, and the microbial glycosylation method [29-30].

Cyclodextrin glucanotransferase (CGTase) can transfer the glucosyl group of starch or cyclodextrin to other monosaccharides by transglucosylation, so it can be used to catalyze the introduction of new monosaccharides on the glycosyl group of stevioside (SS) by starch or cyclodextrin, thereby achieving the purpose of modifying the taste of stevioside. The use of GTase enzyme to modify stevioside is a mild and environmentally friendly method [31].

Brás H de Oliveira et al. found that the red mold Gibberella fujikuroi contains hydrolases that degrade stevioside. By fermenting and culturing this fungus, the effect of hydrolyzing stevioside and increasing the relative content of RA can be achieved [32]. However, the red mold is slow and not very efficient. Our research group has found through studies of Bacillus luteus and subsequent series of research that the conversion efficiency of these microorganisms is much higher than that of Aspergillus oryzae and can efficiently convert stevioside to sweet tea glycoside [33]. Using Bacillus megaterium, Aspergillus versicolor, etc., stevioside and other components can be biotransformed to increase the relative content of RA components with a better sweet taste or obtain other rare steviol glycosides [34].

4. The safety of stevia and stevia

Steviol glycosides are very stable and will not decompose when cooked or baked at temperatures up to 200 °C. They do not accumulate in the body and are suitable for people suffering from obesity, diabetes, hypertension, atherosclerosis and dental caries. They can also be safely consumed by patients with phenylketonuria (PKU), making them highly safe. Steviol glycosides have long been used as a food additive in China. The national standards GB8270 “Food Additive Steviol Glycosides” and GB2760 “Hygienic Standards for Uses of Food Additives” provide detailed specifications.

Healthy people, as well as diabetics and hypertensives, can safely use steviol glycosides [35]. Tests and pharmacological experiments at home and abroad on acute, subacute and chronic accumulation have proved that stevioside has no toxic side effects. The inhabitants of the place of origin have been consuming stevia for more than 400 years, and no adverse effects have been found so far. According to the safety and toxicity test research on stevia in China, it is stipulated that stevia can be used in food and beverages according to the required amount, and it has become a sweetener with the same safety level as sucrose. In 2009, the US FDA considered stevioside to be safe. In September 2009, the French authorities approved RA (97%) as a food additive, and in January 2010 it was also authorized as a table sweetener. On April 14, 2010, the European Food Safety Authority announced a positive opinion on stevioside and RA [36].

5 Conclusion

China is the world's largest producer of stevioside, accounting for 80% of the global market [37], but domestic consumers' understanding of stevioside is limited to its use as a sweetener, and they know very little about its pharmacological value. How to expand domestic demand for stevioside and raise domestic consumer awareness is an important issue that should be considered. Stevia and its glycosides are currently the world's trendy sweeteners and health products. They do not affect blood sugar levels or interfere with insulin secretion after consumption. The dosage used as a sweetener has no effect on the glycemic index (GI), which can provide diabetic patients with more flexible options in terms of total calorie intake and help control weight.

Stevia is physically and chemically stable, and its shelf life can be greatly extended compared to sucrose products. The use of sucrose-free products in food may cause browning reactions, which is beneficial for maintaining the natural color of beverages and foods. The use of steviol glycosides to replace part of the sucrose in processed foods and beverages not only reduces costs, but also meets the requirements of the gradual development of low-sugar foods and beverages, and can be used as health products or drugs [38-39], new varieties of stevia tea [40] and stevia wine [41] . Stevia glycoside sales are increasing day by day, with sales of just one company, Purac, reaching 127 million US dollars (800 million RMB) in 2015 [42]. Therefore, as natural products with multiple functions, stevia and stevia sugar will have increasingly broad application prospects in new health care applications.

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