Czech J. Food Sci., 34, 2016 (4): 281–299 Review doi: 10.17221/335/2015-CJFS Stevioside and Rebaudioside A – Predominant Ent-Kaurene Diterpene Glycosides of Therapeutic Potential: a Review Ena GUPTA1, Shalini PURWAR1, Shanthy SUNDARAM1, Prashasti TRIPATHI 2 and Gyanendra RAI 1,2 1Centre for Biotechnology and 2Centre of Food Technology, University of Allahabad, Uttar Pradesh, India Abstract Gupta E., Purwar S., Sundaram S., Tripathi P., Rai G. (2016): Stevioside and rebaudioside A – predomi- nant ent-kaurene diterpene glycosides of therapeutic potential: a review. Czech J. Food Sci., 34: 281–299. Stevia rebaudiana (Bertoni) is a Paraguayan perennial herb of the family Asteraceae. The leaves contain a great amount of secondary metabolites with a wide range of important biological activities commonly known as steviol glycosides which differ in their molecular configuration, power of sweetness and their taste profile. Out of various steviol glyco- sides, the main compounds of interest are diterpenoid glycosides of ent-kaurene type extracted from the leaves of this plant as non-toxic, thermally stable, low-calorie natural sweeteners stevioside and rebaudioside A. These glycosides are a high-quality sugar substitute or dietary supplement with diverse applications in the medicinal world along with the food and beverage industry. This review article is aimed at the chemistry of stevioside and rebaudioside A, possible biosynthetic pathways, their metabolism and acceptable daily intake along with a broad spectrum of pharmacological and therapeutic applications. Keywords: Stevia rebaudiana; secondary metabolites, therapeutic applications; sweetener Stevia rebaudiana (Bertoni) (Asteraceae) is a per- the North and South American genus S. rebaudiana ennial herb native to Paraguay and Brazil. This plant has been found to produce these sweet tasting steviol is used all over the world as it possesses medicinal glycosides at high concentration levels. Stevioside and commercial importance. It contains a significant (triglucosylated steviol) being the most predominant amount of important nutrients and minerals neces- ent-kaurene type diterpene glycoside, approximately sary for regulating and maintaining various metabolic 3–8% of dried leaves, was first isolated in the first dec- processes in the body (Lemus-Mondaca et al. 2012). ade of the twentieth century in impure form (Bertoni The leaves of S. rebaudiana are extensively studied 1905, 1918) but its final structure was not elucidated as a source of high potency sweet tasting. Natural for nearly sixty years (Mosetting et al. 1963). Later, constituents of the plant are ent-kaurene diterpene (Chaturvedula & Prakash 2011) isolated a new glycosides – stevioside, rebaudiosides A, B, C, D, and diterpenoid glycoside, 13-[(2-O-β-d-glucopyranosyl- E, dulcoside A, and steviolbioside. The foremost active β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid- sweet tasting, non-toxic tetracyclic diterpene steviol (4-O-(2-O-α-d-glucopyranosyl)-α-d-glucopyranosyl- glycosides of particular interest are stevioside and β-d-glucopyranosyl) ester (1) from the commercial leaf rebaudiosides A. The structure of these glycosides extract of Stevia rebaudiana together with the important consists of a diterpene ent-kaurene skeleton, linked sweet ent-kaurene diterpene glycosides stevioside, to a number of glucose units. Out of 230 species in rebaudioside A-G, rubusoside, and dulcoside A. Supported by the Department of Science and Technology (DST), New Delhi, India, under a Women Scientist Project Scheme (WOS-A), vide letter No. SR/WOS-A/LS-668/2012. The authors have declared no conflict of interest. 281 Review Czech J. Food Sci., 34, 2016 (4): 281–299 doi: 10.17221/335/2015-CJFS These non-caloric natural products taste intensely glycosides which are also present in the leaf extract sweet and are estimated to be 150 to 300 times sweeter contributing to low-calorie sweetness and bioactive than sucrose on a weight basis (Richman et al. 1999; properties. Potzel & Brouns 2012). Rebaudioside A exhibits Besides sweetness, various medicinal activities more sweetness and palatable taste profile than other of stevioside and rebaudioside A have been identi- associated steviol glycosides. The Joint FAO/WHO fied which include antihyperglycaemic (Jeppesen Expert Committee on Food Additives (JECFA) in et al. 2002; Gregersen et al. 2004), antineoplastic 2007 laid down specifications that steviol glycoside (Mizushina et al. 2005), anticariogenic (Das et al. sweeteners should consist of at least 95% of the 1992), antihypertensive (Chan et al. 2000), anti- known steviol glycosides (JECFA 2007). inflammatory (Yasukawa 2002), and antioxidant In Europe, United States, China, Japan, Russia, activity (Žlabur et al. 2015). Currently, numerous Korea, and Brazil stevioside and rebaudioside A have reviews have been published concerning the valu- been approved for use as a sweetener (Kinghorn able and abundant potential of steviol glycosides as a & Soejarto 1985). A difference in the structure sweetener in beverages and variety of food products of stevioside and rebaudioside A is having one less including soy sauce, sea foods, pickled vegetables, glucose moiety. Recent development in the field of and confectionary or bakery products. The main research of these glycosides and their derivatives focus area of this article is to review systematic for extracting, isolating, purifying, and modifying literature and to summarise the comparative study them is an ever growing field. The published lit- on the structural features, biosynthetic pathways, erature reported different analytical techniques for safety evaluation, metabolic, pharmacological, and determination of steviol glycosides in S. rebaudiana therapeutic applications of the major steviol glycoside which include an electrospray ionisation technique sweeteners stevioside and rebaudioside A existing used in mass spectrometry (ESI-MS) (Jackson et in S. rebaudiana leaves. al. 2009), analysis of infrared light interacting with a molecule via infrared spectroscopy (Dacome et al. 2005; Hearn & Subedi 2009), liquid chromatogra- Chemistry of steviol glycosides – stevioside phy/mass spectrometry (Wang et al. 2004), capillary and rebaudioside A electrophoresis (Mauri et al. 1996; Dacome et al. 2005), high-performance thin layer chromatography The effort to explain the chemical structures of (HPTLC) (Chester 2012; Londhe & Nanaware S. rebaudiana sweeteners started at the beginning of 2013) and one of the most reliable and simplest the twentieth century, which was from 1901 to 2000; methods recommended by the FAO/WHO Joint but the progress was not fast. In different species of Expert Committee on Food Additives (JECFA) at Stevia plants almost thirty ent-kaurene diterpene gly- the 73rd Meeting (JECFA 2010) is high-performance cosides have been isolated that are commonly known liquid chromatography (HPLC) (Woelwer-Rieck as steviol glycosides – the aglycone part of such gly- et al. 2010; Bergs et al. 2012; Tada et al. 2013). On cosides is steviol (ent-13-hydroxy kaur-16-en-19-oic the other hand, these analytical methods essentially acid) which is involved in constructing a C19-ester focused on the quantification of either stevioside linkage between the C19-carboxylic function and a or rebaudioside A and to a lesser extent on minor glucose unit, along with the formation of ether linkages Table 1. The chemical identity of stevioside and rebaudioside A Steviol Common Chemical Chemical Formula C.A.S. glycosides name name formula weight number 13-[(2-O-β-d-glucopyranosyl-β-d-gluco- Stevioside stevioside pyranosyl)oxy]kaur-16-en-18-oic acid C38H60O18 804.88 57817-89-7 β-d-glucopyranosyl ester 13-[(2-O-β-d-glucopyranosyl-3-O-β-d- glucopyranosyl-β-d-glucopyranosyl)- Rebaudioside A rebaudioside A C H O 967.03 58543-16-1 oxy]kaur-16-en-18-oic acid β-d-gluco- 44 70 23 pyranosyl ester 282 Czech J. Food Sci., 34, 2016 (4): 281–299 Review doi: 10.17221/335/2015-CJFS Figure 1. The structures of sweet ent-kaurene diterpene glycosides: aglycon steviol, stevioside, and rebaudioside A using its C13-hydroxy group with combinations of in the leaves, a slight amount is in the stem and an glucose, xylose, and rhamnose moieties. Stevioside and untraceable amount in the roots (Pól et al. 2007). rebaudioside A are two sweet tasting diterpene steviol The primary seven steps involved in biosynthesis glycosides found naturally in the leaves of the Stevia of steviol glycosides are similar to the MEP (2-C- plant similar in structure to rebaudioside A having methyl-d-erythritol-4-phosphate) pathway when iso- one more glucose moiety as compared to stevioside. pentenyl diphosphate (IPP), dimethylallyl diphosphate The chemical identities and key chemical identifiers (DMAPP), and geranylgeranyl diphosphate (GGDP) for the two main sweetener components of the genus are synthesised (Wanke et al. 2001). Subsequently, Stevia are presented in Table 1. the next four steps are similar to the gibberellic acid The glucosyl and sophorosyl residue is present (GA) biosynthesis pathway which involves synthesis in the stevioside attached to the aglycon steviol, fi- of kaurenoic acid from geranylgeranyl diphosphate nally showing a cyclopentanoperhydrophenanthrene (GGDP). The last five steps include the steviol glyco- skeleton. Individually the C4 and C13 of steviol are side (SG) biosynthesis pathway (Figure 2) (Hanson linked to the β-glucosyl and β-sophorosyl group. & White 1968). The rebaudioside A has the same structure as that of In the presence of ent-copalyl