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       Thai Bitter Cucumber is the dried green mature fruit of Momordica charantia L.  (M. muricata Willd.) (Family Cucurbitaceae), Herbarium Specimen Number:  DMSC 5159, Crude Drug Number:  DMSc 0889.

Constituents  Thai Bitter Cucumber contains charantin, a mixture of sitosteryl and stigmasteryl glucosides, and bitter triterpenoids (e.g., momordicins).  It also contains polypeptides  (e.g., p-insulin), phenolic compounds, etc.

Description of the plant  (Figs. 1a, 1b)  Annual or perennial climber, monoecious, 3 to 4 m long, slender, angled, many-branched, pubescent; tendril unbranched, up to 20 cm long, slender.  Leaves simple, spirally arranged, suborbicular to orbicular, 4 to 12 cm long, 2.5 to 12 cm wide, deeply palmately, 5- to 7(–9)-lobed, lobe ovate-oblong or ovate-elliptic, apex acute or obtuse, base cordate, margin crenate, mucronate or irregularly toothed, glabrous or pubescent, pellucidly dotted; petiole 1.5 to 7.5 cm long.  Flower solitary, axillary, yellow; sepals 5; petals 5.  Male flower peduncle 2 to 6 cm long, slender; bract green, reniform to suborbicular, 0.5 to 1.5 cm wide, apex more or less mucronate, margin subentire; receptacle cup-shaped, 2 to 4 mm long and wide; sepal ovate-elliptic (-oblong), 4 to 6 mm long, 2 to 3 mm wide, acute, pale green; petal obovate to oblong, 1 to 2 cm long, 0.3 to 1.5 cm wide, apex more or less mucronate, basal scales 2; stamens 3, filament 1.5 to 2 mm long, free, inserted in the throat of cup-shaped receptacle, anthers coherent; disc cup-shaped, about 1.5 mm in diameter.  Female flower peduncle 0.5 to 5 cm long; bract 0.1 to 1 cm in diameter; sepal oblong-lanceolate, 4 to 6 mm long, 2 to 3 mm wide; petal smaller than those of male flower,  0.7 to 1.2 cm long; ovary inferior, fusiform or narrowly rostrate, ribbed, warty or papillose, long-beaked, style about 2 mm long, stigma 3-lobed, lobe bifid or notched.  Fruit pendulous, fusiform or ellipsoid, 2 to 8.5 cm long, up to 3.5 cm wide, tapering towards apex, beaked, longitudinally 8- to 10-ridged, tuberculate, orange when ripe, splitting incompletely with 3-valved exposing orange pulp; fruit stalk 3.5 to 15 cm long.  Seeds few to numerous, oblong, 0.8 to 1.3 cm long, 5 to 9 mm wide, flattened, sculptured, whitish or brown, embedded in reddish pulp.

Description  Odour, characteristic; taste, bitter. 

      Macroscopical  (Fig. 1a)  Transverse or oblique pieces, varying in size, up to 3 cm in diameter; externally warty, greenish to brownish; internally creamy white to pale brown.   

      Microscopical  (Figs. 2a, 2b, 2c)  Transverse section of the fruit shows epicarp, mesocarp, endocarp, seed coat, and cotyledons.  Epicarp, a layer of rectangular cells with stomata and glandular trichomes.  Mesocarp, diffentiated in 3 zones:  thin-walled parenchyma cells which increase in size from periphery towards the interior, the smaller cells near the periphery

contained most of chloroplasts, vascular bundles found at the innermost part of this zone; moderately thick-walled parenchyma cells, composed of several layers of loosely packed cells with intercellular spaces, containing numerous starch grains; and thin-walled  parenchyma cells, several layers of cells containing cuboidal protein crystals and numerous  starch grains.  Endocarp, a layer of small thin-walled cells containing starch grains.  Seed coat composed of epidermis, a layer of thin-walled cells filled with starch grains; sclerenchyma, several layers of lignified thick-walled or pitted cells containing starch grains; parenchyma, several layers of thin-walled cells.  Cotyledons 2, composed of a layer of epidermis and reserved parenchyma cells which are fairly large and filled with oil globules.

    Thai Bitter Cucumber in powder possesses the diagnostic microscopical characters of the unground drug.  Thick-walled parenchyma cells containing starch grains; lignified  thick-walled or pitted cells of sclerenchyma of seed coat; occasionally uniseriate-stalked glandular trichomes; and occasionally cuboidal protein crystals are characteristic. 

Warning 

       1. It should not be used in nursing women and children unless recommended by  a physician.  

       2. It should be used with caution in patients with existing liver diseases including alcoholic cirrhosis.

       3. Concomitant use with oral hypoglycemic agents and insulin intake should be  avoided due to hypoglycemic risks.

Additional information  It is commonly used with other herbal drugs in Thai traditional herbal preparations.

Packaging and storage  Thai Bitter Cucumber shall be kept in well-closed containers, protected from light, and stored in a dry place.

Identification 

      A. Reflux 1 g of the sample, in powder, with 10 mL of ethanol for 15 minutes and filter.  Evaporate the filtrate to dryness in a porcelain dish.  Add 5 drops of acetic anhydride to the residue and then slowly add 1 drop of sulfuric acid along the inner side of the dish:  a purple colour develops and gradually changes to brownish black.

      B. Carry out the test as described in the “Thin-Layer Chromatography” (Appendix  3.1), using silica gel GF254 as the coating substance and a mixture of 90 volumes of dichloromethane and 10 volumes of methanol as the mobile phase and allowing the solvent front to ascend 9 cm above the line of application.  Apply separately to the plate as bands of 7 mm, 20 μL each of the following two solutions.  Prepare solution (A) by refluxing 1 g of the sample, in powder, with 5 mL of a mixture of equal volumes of dichloromethane and methanol in a water-bath and filtering.  For solution (B), dissolve 1 mg of charantin in 1 mL of  a mixture of equal volumes of dichloromethane and methanol.  After removal of the plate, allow it to dry in air and examine the plate under ultraviolet light (366 nm) through the cut-off filter; two red fluorescent bands are observed.  Spray the plate with a 10 per cent v/v  solution of sulfuric acid in ethanol and heat at 110° for 1 to 2 minutes; the chromatogram obtained from solution (A) shows a violet band (hR_f value 28 to 30) corresponding to  the charantin band from solution (B).  Other several bands of different colours are observed (Table 1); see also Fig. 3. 

Table 1 hR_f Values of Components in the Extract of the Fruits of Momordica charantia L.​

       *charantin

Loss on drying  Not more than 16.0 per cent w/w after drying at 105° to constant weight (Appendix 4.15).

Foreign matter  Not more than 2.0 per cent w/w (Appendix 7.2).

Acid-insoluble ash  Not more than 0.1 per cent w/w (Appendix 7.6).

Total ash  Not more than 13.0 per cent w/w (Appendix 7.7).

Ethanol-soluble extractive  Not less than 1.0 per cent w/w (Appendix  7.12).

Water-soluble extractive  Not less than 4.5 per cent w/w (Appendix 7.12).

Dose  500 mg to 1 g three times a day.