The nonsaccharide sweetening agents, having low calorific values and therefore health compatible, unlike sucrose^1,2, are: terpenoids, steroids, steroidal saponins, dihydrochalcones, proteins, etc. On the other hand, due to regular use of traditional saccharide sweetening agents, except fructose syrup, human diseases such as dental caries, cardiovascular disease, diabetes mellitus, obesity and micronutrients deficiency have increased alarmingly³. Furthermore, synthetic sweetening agents such as saccharin, aspartame, and cyclamate used as substitute for sucrose in USA have been found to be carcinogenic and more harmful than sucrose⁴. Hence, in Japan, China, USA, Australia and Europe the nonsaccharide sweete-
ners are being consumed. Thus, with the increase in
their demand there is a necessity for identification of these nonsacchariferous plant species, as well as the identification of their active sweet principle. A schematic representation of the types of sweeteners and their origin is given below.

The first plant fruit mentioned as ‘sweet’ in the Bible is fig (Ficus carica L.) (Moraceae); the dried fruit of which was recovered from excavation of Gezar located in Judean Mountains and is dated 5000 BC (ref. 5). The sucrose, derived from Sanskrit word Sarkara, was being extracted from sugarcane in India, and had been identified about 6000–10,000 BC as mentioned in Rig and Atharva Vedas. It was introduced in non-Asiatic continents by Alaxander the Great (c. 325 BC) (ref. 6). Another sweet plant, Saccharum spontaneum, (Kush in Sanskrit) has a mention in Ramayana by Maharishi Balmiki. The plant was used in cloning and culturing of a new child in the place of lost child ‘Lav’ (son of Goddess Sita). This plant accumulates saccharides as the active sweet principle; the structural and chemical formulae are mentioned in Figure 1.

The oldest sweet-tasting plant containing nonsugar principles, for example glycyrrhizin, is Licorice, Glycyrrhiza glabra L., (Leguminosae). Its active sweet principle is 100 times sweeter than sucrose on a unit weight basis. It appears to have been in use approximately around 500 BC (ref. 8). Theophrastus (c. 300 BC), called it as sweet scythian root. Thaumatococcus daniellii (Bernett) Benth. (Marantaceae) was identified in 1855 by Deniell⁹ from which thaumatin was extracted. This was found to be 10,000 times sweeter than 7% sucrose on a molar basis¹⁰. Subsequently in 1905, another intensely sweet plant, European polypody fern, Polypodium valgare L. (Polypodiaceae) was identified¹¹. Sweet principle, osladin, was extracted from its rhizome¹². Presently, as many as 15 species of nonsacchariferous sweet plant have been identified. In this article, are the details relating to these in Indian context.

1. The plant species, Perilla frutescens (L.) Britton (Labiatae), commonly known in various regional languages as: bhanjira (Hindi); ban tulsi (Bengali); jhutela (Kumaun), is indigenous to India and found almost throughout Himalayas up to an altitude of 3500 m and on the hills of Assam and Bihar¹⁴. It is propagated mainly through seeds. Some of its characteristic features are: aromatic, bushy annual height 150 cm. Leaves; broadly ovate, acuminate, coarsely serrate or crenate. Flowers; small, white in axillary and terminal racemes. Nutlets commonly called seed: rounded, pale brown, with reticulate markings, weighing 250 mg to 1 g.

The sweet principle, Perillartin¹⁵ is a type of monoterpenoid. Volatile oil is produced from leaves and flowering tops. Perrilla seeds contain 30–50% volatile oil. The volatile oil provides flavour to sauces, confectionery and is 370–450 times/2000 times sweet as sugar on a unit weight basis, and 4–8 time as sweet as saccharin¹⁶
(Table 1).

2. The plant species Stevia rebaudiana (Bertoni) Bertoni (Compositae) is reported to be native to Paraguay and south Brazil, and cultivated in Japan, southeast Asia, USA, etc.^17,18, but grows in India as well at some semitropical areas, humid Himalayan hilly regions, and humid hills of Assam. It is propagated through seeds and cuttings. The seedlings raised from seeds are transplanted and shoot is harvested after 4–5 months of growth. The ratoon stalk/stubbles give rise to new plants. Its characteristic features are: branched bushy shrub, height usually 40–120 cm. Leaves; small, oblong, serrate and sweet. Flowers; small, usually white. Leaves are harvested for extraction of the sweet agent at the time of the emergence of flower primordea.

The sweet principle, Stevioside¹⁹, is a type of diterpenoid, 200–300 times sweeter than sucrose on a unit weight basis²⁰ (Table 1). Many types of steviosides such as rebaudioside A, B, C, D and E and steviol x–xii are extracted from the leaves. The sweetness in the leaves is two times higher than of inflorescence.

3. The plant species Glycyrrhiza glabra L. (Leguminosae) is commonly known as licorice, liquorice; madhuka (Sanskrit), mulhatti (Hindi). It is native of Mediterranean region and cultivated in France, Italy, Spain, USSR, USA, Middle East and Asia. In India, it is found in Srinagar, Jammu, Deharadun, Baramulla, temperate Himalayan regions and southern Indian hilly districts¹⁴. Deep moist soil, particularly the banks of river which are subjected to periodical inundation, suits the growth of this plant. It is propagated through divisions of crown or rooted cuttings of underground stem. Some of its characteristic features are: Hardy herb or underground shrub with maximum height of 2 m. The underground growth of stem and roots is found to be higher than aerial parts of plants. Leaves; multifoliated and imperipinnate¹⁴. Flowers; axillary spikes, papilionaceous, lavender to violet, Pods; compressed containing reniform seeds. While the underground part in some varieties is made up of a root stock with a number of long branched stem, in other varieties the root stock is stout, and throws off a large number of perennial roots.

The sweet principle, glycyrrhizin (glycyrrhizic acid)⁸ is a triterpenoid (Table 1). Calcium or potassium or magnesium salt of sweet trihydroxy acid, glycyrrhizic acid (C₄₂H₆₂O; m.p. 205ºC-quick decomp.) is found in roots and rhizomes (Figure 3). Ammonium glycyrrhizin, the fully ammoniated salt of glycyrrhizic acid is commercially available and has been found to be 100 times sweeter than sucrose²¹ (Table 1).

4. The plant species Abrus precatorius L. (Leguminosae) is commonly known as Indian liquorice, jequirity gunja (Sanskrit and Marathi), ghungchi and rati (Hindi), kunni (Malayalam), kunch (Bengali). It is indigenously found throughout India, even at altitudes up to 1200 m on the outer Himalayas. It is now naturalized in all tropical countries¹⁴. This plant species is propagated through seeds. Six species of Abrus are available. Two species, A. precatorius and A. laevigatus, are most common in India¹⁴. A. precatorius is a climbing shrub with peripinnate leaves, sensitive to light and changes in weather. The shiny seeds are of the size of small peas, usually bright scarlet and with black eyes, sometimes however white seeds with or without black eyes are also met with. Leaves taste more sweeter than roots. Seeds are poisonous and contain abrin, a poisonous principle. Leaves, roots and seeds are used for medicinal purposes (Figure 4). The sweet principle, glycyrrhizin, is same as that of liquorice²² (Table 1). Abrus precatorius is a substitute for Glycyrrhiza glabra L.

5. The plant species Achras sapota L. (Sapotaceae) is indigenous to South America, but cultivated all over the world including India for its edible fruits. It is available in states of Maharashtra, West Bengal, Tamil Nadu, Karnataka, Kerala, etc.¹⁴. It thrives better in coastal areas. Rich and well-manured sandy soil supports good growth. It is propagated commonly through seeds. However, seed- raised trees are slow in growth and bearing, therefore layering, budding and grafting are practised which results in bearing of fruits within two years. In-arching is a common form of grafting in India.

Three species of Achras are found in India¹⁴. A. sapota L. is an evergreen 6–11 m high tree with a spreading crown. Flowers are seen throughout the year, and fruits ripen mainly during March, April, August and September. Fruit is round or oval berry of 5–10 cm diameter. The seeds (9–12 per fruit) are hard, black and about 2 cm long. Fruit has thin rusty brown skin. The flesh in ripe fruits is yellowish-brown, soft and sweet. The coagulated resinous latex derived from bark is used for making chewing-gum.

6.

The plant species Hydrangea macrophylla (Thunb.) Seringe (Saxifraceae), commonly known as amacha. H. macrophylla, is indigenous to Japan, China and is found in North and South America, and temperate hills of India. It is widely distributed in Ravi east towards Assam, and in Himalayas at altitudes of 1300–3300 m, Garhwal, Kathmora and other hill stations in India¹⁴. It is propagated by cuttings, division or suckers. Five species of Hydrangea are found in India¹⁴. H. macrophylla Seringe is a shrub, about 4 m height. Leaves; elliptic to broadly ovate or abovote, 7–15 cm long, coarsely toothed, and almost glabrous. Flowers; pink, generally flowers on hill stations and requires high light intensity. Flowering is seldom on plains. Sometimes, due to absorption of aluminium on acidic soils, the flower colour changes from pink to blue¹⁴.

7. The plant species Smilax glycyphylla Sm. (Liliaceae) is known as barichob-chini (Hindi), kukardara (Kumaun), harina-shuk-china (Bengali). Smilax glycyphylla Sm, is indigenous to India and is found in Himalayas from Kashmir eastward in Naga to Khasi hills in Assam¹⁴. It is mainly propagated through rhizomes and tuberous roots. Twenty-four species of Smilax are found in India¹⁴. It is a climber with woody, smooth or sparsely prickled stem. Leaves; distant, alternate and ovate–lanceolate. Flowers; in umbels, very small, white berries light to darkblue.

The sweet principle, Glycyphyllin, is a type of dihydrochalcone glycoside²⁵. The extracts of shoot or almost all parts provide sweetening agent. It is 100–200 times sweeter than sucrose²⁶ (Table 3).

8. The plant species Symplococos paniculata Miq. (Simplocaceae) is commonly known as sweetleaf, sapphire berry, lodhra (Sanskrit), ludh (Hindi). A large number of species of genus Symplococos are found in warmer parts of Asia, Australia, and America. S. paniculata Miq. is indigenous to India and commonly found in the Himalayas from Punjab to Assam and in the Khasi hills, occurring at altitudes between 600 and 2400 m¹⁴. It is mainly propagated through seeds. Sixty-eight species of Symplococos are found in India¹⁴. S. Paniculata Miq. is known as sweet leaf and sapphire berry. It is a deciduous shrub or a tree, 12 m in height. Leaves; obvate, 6.25 cm ´  2.50–3.75 cm in size, softly pilos beneath. Flowers; white, fragrant, in terminal panicle. Fruits; blue, drupaceous, usually one seeded.

The sweet principle, Trilobatin, is a type of dihydrochalcone glycosides²⁷. It is 400–1000 times sweeter than sucrose (Table 3). A water-soluble fraction from the bark has been reported to exhibit antioxidative activity. Seeds contain oil. Leaves are used as fodder. Further studies are required on quantity and distribution of sweet principles in different parts of this plant.

9. The plant species Citrus aurantium L. (Rutaceae) is commonly known as seville orange, khatta (Hindi), karna (Malayalam). This plant is indigenous to India¹⁴ and is being cultivated on a large scale. Earlier its cultivation centred around Guntur district of Tamil Nadu, specially for its fruit, orange. It is propagated through seed and

grafting. Plant is a medium-sized thorny tree with broadly winged leaf stalk. Flower; pentamerous, usually white, hermaphrodite, complete and hypogynous with enlarged and very conspicuous water secreting annular-shaped disk below the gynoecium. Fruit; round and orange in colour when ripe. Rind; aromatic bitter and pungent. Pulp; acidic.

The sweet principle is Neohesperidin dihydrochalcones²⁸. The flavonoid parent compound neohesperidin is bitter and is present in the peels.

Dilute alkali extracts the sweet principle. These are about 1000 times sweeter than sucrose²⁸ (Table 3).

10. The plant species Citrus paradisi Macf. (Rutaceae) is commonly known as grape fruit. It is indiginous to west Indies and cultivated in India both in subtropical and tropical areas¹⁴. It is propagated through seed and grafting. Plants are fairly large trees, 6–14 m high with smaller leaves than pummelo and peteoles less broadly winged than pummelo. Flowers; large, born singly or in small clusture in the axil of leaves. Fruits; round or pear shaped (Figure 5) with white or pink flesh. Juice; plentiful and sour.

The sweet principle, Naringin is a type of dihydrochalcone²⁸. The flavonoid parent compound naringin is bitter and present in peels. Extract in dilute alkali gives sweet principle. It is somewhat less than 1000 times sweeter than sucrose²⁸ (Table 3), commercialized and could also be used to prepare neohesperidin.

11. The plant species Citrus sinensis L. (Rutaceae) is commonly known as betavian, sweet orange, musambi (Hindi), narangi (Bengali), kamala (Gujarati), nembia (Marathi)¹⁴. It is native of India and China and is being cultivated widely in subtropical regions as most valued commercial citrus of the world. It is cultivated widely in India¹⁴. It is propagated by seeds, cuttings, layering and budding. Seeds germinate in about 20 days after sowing. A spreading, evergreen tree attains a height of about 10 m. Petal; narrow and winged. Fruit; globose, rounded at the apex, golden yellow or orange when ripe, rind; fairly thick, tightly adherent. Pulp; yellow, orange or reddish, fairly sweet, juicy and nutritious.

12. The plant species Citrus limon L. (Rutaceae) is commonly known as lemon, baranibu and jambira (Hindi), idalimbu (Marathi), pariya and yelumichai (Tamil). Wild stock of C. limon L. is native of northwest region of India ascending to 1335 m¹⁴. Lemon is cultivated in almost all parts of India. It is propagated through seed, layering, grafting and budding. Some of its characteristic features are: A straggling bush or small tree with thorny branches and attains a height of 3–4 m. Peteole; wingless or very slightly winged. Fruit; oblong or ovoid, usually with a nipple-shaped extremity, bright yellow. Rind; thick. Pulp; acidic, pale yellow.

13. Cynara scolymus L. (Compositae) is commonly known as globe or burr artichoke, hathichak and hathichoke (Hindi), hathichoke and hathichoke (Bengali). It is native to cold humid mediterranean region/countries. It is cultivated as vegetable crop throughout India, on hills as well as on plains¹⁴, and at places where winter is mild and moist. Medium to light soils are most suitable for its growth. It is propagated by seeds or suckers or offshoots. Plants raised through seeds flower in about 8 months, but those raised from suckers flower earlier and pro-duce uniform-sized flowers. Usually, suckers are plan-ted in plains during August–December and seedlings of 10–12 cm length raised through seeds are planted on hills during February–June. Thirteen spp. of Cynara are found in India¹⁴. C. scolymus L. is a thistle-like perennial herb of 1.0–1.8 m height. Two varieties, green globe and purple globe are cultivated. Leaves: medium size, bitter, in taste. The globular immature flowers are used as vegetable. Flowers are harvested for use before involucral bracts start opening. Thick receptacle are known as heart, and flesh base of involucral bracts from the main edible portion. Floral head is used by patients with diabetic.

The per capita consumption of sucrose (white sugar) in USA, Australia and China has reduced to half in the last several years³¹, since regular use of sugar has been found hazardous to health. This has been possible because of the availability of four commercial nonsaccharide sweetening agents: ammoniated glycyrrhizin; thaumatin; stevoiside; and phyllodulcin (Table 5) besides some other alternative sources of sucrose available as well, for example high fructose corn syrup (saccharide)^2,23. Since nonsaccharide sweetening agents are low in calorific values and most health compatible, their demand is on the increase in Japan, USA, Australia, Europe, China, Thailand, Brazil and other parts of the world. Recently, another sweetening agent, monellin (protein) has been in great demand in Europe².

In India, 13 species of plants that accumulate nonsaccharides as the active sweet principle have been identified. These principles can be grouped as: terpenoides; steroidal saponins; dihydrochalcones; dihydroisocoumarins; proteins, etc. Collection, propagation, cultivation, and establishment of germplasm repository of these plant species are essential. For fast multiplication of these plants, development of suitable techniques are required not only to save them from becoming extinct but also to enable their large-scale cultivation. Furthermore, simple techniques for the extraction of these principles are required which could be adapted at small-scale level.