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                        Pomelo Rind is the dried exocarp with some unremovable mesocarp of Citrus maxima (Burm.) Merr. [Aurantium maximum Burm., Citrus grandis (L.) Osbeck] (Family Rutaceae), Herbarium Specimen Number: DMSC 5319, Crude Drug Number: DMSc 1224.

Constituents  Pomelo Rind contains flavonoids (e.g., apigenin, hesperidin, and naringin). It also contains volatile oils, coumarins, limonoids, sterols, pectins, etc.

Description of the plant  (Fig. 1)  Tree, up to 15 m tall; stem thorny, irregular branches; young branch usually angular, purplish, pilose. Leaves unifoliolate, alternate, obovate, broadly ovate to elliptic, 5 to 20 cm long, 2 to 12 cm wide, apex obtuse, mucronate, or rounded, base rounded or subcordate, margin entire or crenate, upper surface dark green, coriaceous, with aromatic pellucid dots, lower surface prominently veins, pubescent; petiole articulated, 2 to   7 cm long, broadly winged to nearly wingless. Inflorescence terminal or axillary, racemose, sometimes flowers solitary or clustered, (1‒)2- to 15-flowered, 10 to 30 cm long; rachis hairy; pedicel 1 to 1.5 cm long. Flowering bud purplish, rarely whitish; flower white, calyx green, 4- to 5-lobed, 0.5 to 1 mm long; petals 4 to 5, whitish, ovate or oblong-ovate, 1.5 to 3 cm long, 0.7 to 1.5 cm wide; stamens 20-35, filament 1 to 3 cm long, anther oblong, about 5 mm long; ovary superior, pubescent, 10-to 16-loculed, 4- to 8-ovuled per locule, style about 1.5 cm long, thick, stigma verrucose. Fruit a hesperidium, globose, oblate, or pyriform, 10 to 20 cm in diameter; exocarp and mesocarp 1 to 4 cm thick, exocarp greenish yellow to golden yellow with large prominent pellucid dots, tough, mesocarp white or pale pink, spongy, 1 to 3 cm thick; segments 11 to 18; fruit-pulp numerous, elliptic or ovate, elongate. Seeds numerous, somewhat flattened, ridged, hard.

Description Odour, aromatic, characteristic; taste, slightly bitter.

                        Macroscopical  (Fig. 1)  Dried external rinds with some unremovable mesocarp, roughly cut, easily broken, varied in shape and size; externally yellowish to pale brown and brown bulges; internally whitish, rough.      

                        Microscopical  (Figs. 2a‒2c)  Transverse section of the rinds shows exocarp with some unremovable mesocarp. Exocarp: 1 to 2 layers of yellow greenish epidermal cells, some containing prismatic crystals or oil droplets, covered with thick cuticle layer and stomata. Mesocarp: numerous and various shapes of nonlignified unevenly thick-walled parenchyma, round shape in the outer and loosen elliptic shape in the inner, some containing prismatic crystals or oil droplets; schizolysigenous oil cavities, containing oil droplets; vascular tissue, phloem and xylem.

                Pomelo Rind in powder possesses the diagnostic microscopical of the unground drug. Epidermal layer with stomata, oil droplets, and prismatic crystals can be seen in abundance. Part of oil cavity and thick-walled parenchyma of mesocarp can also be seen.

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

Identification

A. Heat 500 mg of the sample, in powder, with 10 mL of methanol in a water-bath for 15 minutes and filter. To 2 mL of the filtrate, add 1 to 2 pieces of magnesium ribbon, shake well, mix with a few drops of hydrochloric acid, and warm on a water-bath for 5 to 10 minutes: a red precipitate forms.

B. Heat 1 g of the sample, in powder, with 20 mL of water in a water-bath for 15 minutes and filter. To 2 mL of the filtrate, add a few drops of iron(III) chloride TS and shake well: a blue precipitate forms.

C. 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 80 volumes of ethyl acetate, 10 volumes of methanol, and 10 volumes of formic acid as the mobile phase and allowing the solvent front to ascend 10 cm above the line of application. Apply separately to the plate as bands of 8 mm, 15 mL of solution(A) and 5 mL of solution(B). Prepare solution (A) by
sonicating 1 g of the sample, in fine powder, with 15 mL of methanol, for 15 minutes and filtering. For solution (B), dissolve 2 mg of naringin in 2 mL of methanol. After removal of the plate, allow it to dry in air and examine under ultraviolet light (254 nm), marking the quenching bands. The chromatogram obtained from solution (A) shows a quenching band (hRfvalue 34 to 36), corresponding to the naringin band obtained from solution (B). Other four quenching bands are also observed. Subsequently examine the plate under ultraviolet light (366 nm); three blue fluorescent bands are observed. Spray the plate with anisaldehyde TS, heat at 105° for about 10 minutes, and examine under visible light. The band due to naringin is brown. One brown, two green, and six violet bands are also observed (Fig. 3).

Loss on drying  Not more than 10.0 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).

Total ash  Not more than 7.0 per cent w/w (Appendix 7.7).

Ethanol (50 per cent)-soluble extractive  Not less than 28.0 per cent w/w (Appendix 7.12).

Ethanol-soluble extractive  Not less than 10.0 per cent w/w (Appendix 7.12).