Stevia (Stevia rebaudiana Bertoni) is a member of the Compositae (Daisyaceae) family and this plant is also commonly known as honey leaf, sugar leaf and sweet leaf (Dinçel, 2018). Sweet compounds found in stevia leaves are diterpene glycoside (steviol glycoside) compounds, where the main sweetening compound is stevioside. Stevia production occurs in three ways; The first is powder stevia, which is obtained by drying, grinding and packaging the direct stevia leaves, the other two are concentrated stevia extract and powdered stevia extract. Stevia sweetener; Besides being 250-300 times sweeter than sucrose, having high heat and pH stability, baking and oven stability, dissolving in alcohol, not having a metallic taste in the mouth, the biggest feature is that it is obtained naturally (İnanç, 2009).
According to some researchers, it has been reported to have antihypertension, antihyperglycemic and anti-human rotavirus healing properties (İnanç, 2009).
Compared with other sweeteners, stevia has been found to have positive effects on phenylketonuria and diabetes patients. It has been stated that especially steviol glycosides can replace sucrose and can be used easily by patients with obesity, hypertension and diabetes (İnanç, 2009).
Free radical production plays a role in the pathogenesis of diabetes, therefore, free radicals are effective in the pathophysiology of various pathways and different mechanisms of diabetes complications. A model of human type II diabetes can be established by administering nicotinamide (NA) and streptozotocin (STZ) to rats. The aim of this study was to determine the effects of Stevia rebaudiana Bertoni (SrB) and L-NNA (N-nitro L-arginine) on free radical formation in STZ-NA-induced type II diabetic rats. In this study, rats were treated with SrB and L-NNA 5-8 weeks after diabetes was induced. Glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) levels were determined in liver homogenates and erythrocyte hemolysates. At the same time, nitric oxide synthase (NOS) levels were measured in liver homogenate and serum. To examine the histological changes in diabetes, liver tissue samples were stained with hematoxylin-eosin and examined with a light microscope. Although fasting and postprandial blood sugars were higher in diabetic groups, blood sugar levels decreased significantly in treated diabetic groups. Although the erythrocyte MDA levels of the stevia-treated diabetic group decreased, L-NNA treatment increased lipid peroxidation in both the control and L-NNA-treated diabetic group. No difference was detected in terms of tissue CAT, NOS and erythrocyte SOD and CAT activities compared to the control. While normal histological structure was observed in the liver samples of the control group, pycnotic nuclei and necrotic cells with eosinophilic cytoplasm and sinusoidal dilatation were detected in the liver tissues of the diabetic control group. Compared with the diabetic control group, hepatocyte structure was normal in the diabetic L-NNA group. However, it was determined that SrB and L-NNA treatment provided high protection in hepatocytes. Our findings showed that SrB and L-NNA treatment in diabetes lowers blood glucose levels, has some positive effects on oxidative and histological changes, however, L-NNA, an NOS inhibitor, is less effective on type II diabetes compared to SrB(Özbayer). ,2011).
Research on how stevia may affect blood sugar in people with diabetes is inconsistent. Some early studies show that taking 1000mg of stevia leaf extract containing 91% stevioside daily can reduce blood sugar by 18% after meals in people with type 2 diabetes. However, other research shows that taking 250 mg of stevioside 3 times daily does not reduce blood sugar levels or HbA1c (a measure of blood sugar levels over time) after three months of treatment.
It is not clear how stevia will affect blood pressure. Some research shows that taking 750-1000 mg of stevioside, a chemical compound in stevia, daily lowers systolic and diastolic blood pressure. However, other studies show that the use of stevioside does not reduce blood pressure (Bilgi, 2021).
In addition, it has been stated in some studies that polyphenol oxidase and peroxidase, which are found as natural inhibitors in the aqueous extracts of Stevia rebaudiana, reduce the use of chemical additives added to foods and reduce the harmful effects of these additives. In another study, it was proved that the maximum concentration of steviol in the blood of hamsters fed with steviol at doses of 250 mg/kg body weight per day is not toxic (Dinçel,2018).
The FDA has stated that stevia cannot be used as a food additive (food preservative) because there are not enough findings on it yet, but it has also been stated that it can be used safely as one of the food ingredients (İnanç, 2009).
Agave syrup is a naturally sweet substance produced by cooking agave pines. Agave syrups are in great demand as sugar substitutes due to their low glycemic index, antioxidant capacity and antibacterial properties (Mellado-Mojican et al.2015). Its fructose content is high (85-90%), sweetening power is 1.4, glycemic index is 11-15, calorie value is 3.1 kcal/g (İşgören,2019).
The F/G ratio is an indirect measure of sweetening capacity. When comparing the F/G ratio among natural sweeteners, Agave syrups had the highest F/G ratios, while corn and cane sugar syrups had the lowest. Therefore, agave syrups exhibit a higher sweetening capacity compared to other natural sweeteners (Mellado-Mojican et al.2015).
The main carbohydrates in agave sap are complex forms of fructose, and one of them is inulin, a polymer of fructose. In this case the sap is not very sweet. The agave extract is heated to 140°F for about 36 hours. Complex fructoses are hydrolyzed and broken down into fructose units. Thus, the solution becomes rich in fructose. Agave Syrup is advertised as “low glycemic” and marketed for diabetics. Agave contains low amount of glucose (10%). However, it contains an unusually high fructose concentration (90%) compared to glucose. Therefore, it has a low glycemic index (Kohler, 1998). Therefore, it should be noted that the risks associated with excessive fructose consumption are also in question for agave syrup (İşgören,2019).
The most known of the disaccharides, sucrose, consists of a glucose and a fructose molecule. It is absorbed by breaking down into glucose and fructose in the small intestines. It is naturally found in excess in sugar cane and sugar beet, and in small amounts in honey, fruits, vegetables and nuts. Natural disaccharides are first hydrolyzed to their monosaccharides in the small intestine, then they are absorbed and metabolized to give energy (İşgören,2019). Sucrose is the most used sugar in the food industry and is a popular ingredient often used to achieve sweetness. It is extracted from sugar cane or sugar beet; baking, beverage, confectionery, gel and jam etc. It is used as an industrial sweetener (Konar, 2019).
It is recommended that consumption of simple sugar may adversely affect diabetes control, therefore, sucrose intake should not exceed 10% of the total daily energy intake (Öztürk,2019).
Sweeteners are important sugar substitutes used to enhance the flavor of foods and beverages by avoiding excessive energy intake. Some studies have shown that sweeteners can be used as a potential body weight management tool by showing a positive role in body weight loss. However, some studies have shown that sweeteners have an active metabolic role in the human body and may impair human metabolism by inducing glucose intolerance, causing obesity and metabolic syndrome. Sweeteners are the group whose effect on the intestinal microbiota has been studied the most. There are approximately 10 times more microorganisms (approximately 100 trillion) in the gastrointestinal tract of humans than the number of somatic cells in their bodies. The most common in the gut microbiota, which includes about 1000 different species; Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, Verrucomicrobia, Cyanobacteriaand actinobacteriatypes (Öztürkcan, 2020).
In a study on mice, bacterial changes in the intestinal flora were observed after 3 days of consumption of 20% sorbitol or sucrose. Sorbitol consumption did not show a significant change on bacteria, and a decrease was observed in the total aerobic and anaerobic numbers in the stool in sucrose consumption (Öztürkcan, 2020).
The sweetness of the fruits of Thaumatococcus danielli (Marantaceae), an African herb, comes from the protein mixture called ‘Thaumatin’ I, II and III. The mixture of sweet proteins is called ‘Tallin’. The molecular weight of all components is 2200u. Tallinn is a commercial sweetener widely used in Japan and England (Tanker, 1993).
It is 2000-3000 times sweeter than sucrose. It is stable in hot and acidic solutions. Its solubility in water is high. It is a low-calorie sweetener. It is also used for flavoring as well as sweetening properties. Defined as GRAS by the FDA. It has also been approved in the European Union since 1984. Its ADI value is 50 mg/kg/day(İşgören,2019).
Thaumatin maintains its stability over a wide pH range. It is not suitable for use in products that will be subjected to high temperature heat treatment due to its instability against temperature. Its solubility in water is also very high and it is possible to prepare even a solution of >1000g/L. The use of thaumatin as a sweetener in food and beverages is allowed in Israel, Japan and European Union countries, and it is allowed to be used as a flavor enhancer in beverages, jams and jellies, dairy products, instant coffee and teas, and gum in the United States (Yılmaz, 2011).