Nutrient composition of the edible leaves per 100 g based on analyses carried out in Nigeria was reported as moisture 58.4 g, energy 159 kcal, protein 6.8 g, fat 0.6 g, carbohydrate 31.5 g, fibre 0.1 g, ash 1.8 g, vitamin A 52 μg RE, vitamin A 26 RAE μg, β-carotene 310 μg, thiamine 0.45 mg, riboflavin 0.58 mg, niacin 0.54 mg, folic acid 15 μg, vitamin C 7.74 mg, calcium 755 mg, phosphorus 739 mg, iron 14.8 mg and zinc 3.7 mg (CINE 2007).

Hauptmann and Nazario (1950) isolated rhein (1,8-dihydroxyanthraquinone-3-carboxylic acid) along with hydroxymethyl anthraquinones and chrysophanic acid from the alcoholic leaf extract. Physcione, kaempferol, rhein methyl ester diacetate and β-sitosterol (Rao et al. 1975); 1,3,8-trihydroxy-2-methylanthraquinone (aloe-emodin), chrysophanol, deoxycoelulatin, sennoside A, sennoside B, sennoside C and sennoside D (Mulchandani and Hassrajani 1975; Villaroya and Bernal-Santos 1976); aloe-emodin, rhein glycoside and aloe-emodin glycoside (Rai 1978); anthraquinones and anthracene derivatives of rhein, emodol, aloe-emodin, sennosides A and B, 4,5-dihydroxy-1-hydroxymethylanthrone and 4,5-dihydroxy-2-hydroxymethylanthrone (Fuzellier et al. 1982); aloe-emodin and chrysophanol (Harrison and Garro 1997), isochrysophanol and physcion-l-glucoside (Smith and Sadaquat 1979); rhein (cassic acid) (Palanichamy et al. 1991); and aloe-emodin (1,8-dihydroxy-3-(hydroxymethyl) anthraquinone), sitosterol and stigmasterol (Hofileña et al. 2000), 3,5,7,4′-tetrahydroxy flavone and 2,5,7,4′-tetrahydroxyisoflavone (Rahaman et al. 2006, 2008) were isolated from the leaves. Kaempferol-3-O-gentiobioside was the major flavonoid glycoside in Senna alata (Moriyama et al. 2003c) The mature leaf was found to contain the highest content of this metabolite. The contents ranged from 2.0 to 5.0 % and 1.0 to 4.0 % in mature and juvenile leaves, respectively. Kaempferol-3-O-gentiobioside was not detected in the seed. Earlier, Moriyama et al. (2001) reported the disappearance of kaempferol 3-gentiobioside in the sun-dried leaves, while there was little or no change in the kaempferol 3-gentiobioside concentration in the heat-treated leaves when incubated in an aqueous solution, suggesting a possible presence of enzymatic activities in the sun-dried leaves. They concluded that heat treatment may be a good method to stabilize kaempferol 3-gentiobioside in Cassia alata leaves.

Hazni et al. (2008) isolated kaempferol, kaempferol 3-O-β-glucopyranoside, kaempferol 3-O-gentiobioside and aloe-emodin from the leaves. Cassiaindoline, a dimeric indole alkaloid (Villaseñor and Sanchez 2009) and kaempferol-3-O-β-d-glucoside (astragalin) (Saito et al. 2012) were isolated from Cassia alata leaves. Four anthraquinones (rhein (cassic acid), aloe-emodin, emodin and chrysophanol) were isolated from Senna alata leaves (Panichayupakaranant et al. 2009). Twelve compounds were isolated from C. alata leaves and identified as chrysoeriol (1), kaempferol (2), quercetin (3), 5,7,4′-trihydroflavanone (4), kaempferol-3-O-β-d-glucopyranoside (5), kaempferol-3-O-β-d-glucopyranosyl-(1→6)-β-d-glucopyranoside (6), 17-hydrotetratriacontane (7), n-dotriacontanol (8), n-triacontanol (9), palmitic acid ceryl ester (10), stearic acid (11) and palmitic acid (12) (Liu et al. 2009). Six compounds (kaempferol, kaempferol-O-diglucoside, kaempferol-O-glucoside, quercetin-O-glucoside, rhein and danthron) were isolated from the aqueous leaf extract (Saito et al. 2010). Leaves were also found to contain saponins (1.22 %), flavonoids (1.06 %), cardiac glycosides (0.20 %), cardenolides and dienolides (0.18 %), phenolics (0.44 %) and alkaloids (0.52 %) (Yakubu and Musa 2012).

The essential oil obtained by hydrodistillation of leaves of C. alata collected in Gabon afforded 44 compounds representing 92.5 % of the oil; the major constituents were linalool (23.0 %), borneol (8.6 %) and pentadecanal (9.3 %) (Agnaniet et al. 2005). The antioxidant activity of the oil was found to be low compared to that of butylated hydroxytoluene (BHT). Fifteen out of twenty-five constituents of C. alata leaf essential oil were identified in trace amount (i.e. <0.1 %) (Ogunwande et al. 2010). The oil was dominated by mono- and sesquiterpene compounds (48.7 and 47.9 %, respectively). The essential oil constituents were 1,8-cineole 39.8 %, β-caryophyllene 19.1 %, caryophyllene oxide 12.7 %, germacrene D 5.5 %, α-selinene 5.4 %, bicyclogermacrene 5.4 %, limonene 5.2 %, α-cadinol 4.2 %, α-phellandrene 3.7 %, (E)-2-hexenal 3.3 %, α-bulnesene 1.0 %, tricyclene trace, (E)-β-ionone trace, benzaldehyde trace, α-terpinene trace, n-pentadecane trace, p-cymene trace, δ-cadinene trace, β-elemene trace, n-hexadecane trace, humulene epoxide II trace, (E)-geranyl acetone trace, tetradecanal trace, α-humulene trace and (E)-β-farnesene trace.

Stems of Cassia alata were found to contain 1,5,7-trihydroxy-3-methylanthraquinone (alatinone) and dalbergin, 2,6-dimethoxybenzoquinone, santal, luteolin, β-sitosterol and β-sitosteryl-β-d-glucoside (Hemlata and Kalidhar 1993) and alatonal (Hemlata and Kalidhar 1994).

Two glycosides, chrysoeriol-7-O-(2″-O-β-d-mannopyranosyl)-β-d-allopyranoside and rhamnetin-3-O-(2″-O-β-d-mannopyranosyl)-β-d-allopyranoside, were isolated from the Cassia alata seeds (Gupta and Singh 1991). Two polyalcohols, glycerol and erythritol, were found in the seeds (Singh 1998). Hydroxyanthracene derivatives were found in the leaves, flowers and pods of Cassia alata (Panichayupakaranant and Intaraksa (2003). A water-soluble galactomannan with molecular weight 26,400 was isolated from the seeds (Gupta et al. 1987). The polysaccharide comprised of heptasaccharide units joined by β-(1→4) linkages.

Two new anthraquinone pigments 1,3,8-trihydroxy-2-methyl anthraquinone (A) and 1,5-dihydroxy-8-methoxy-2-methyl-anthraquinone-3-O-β-d-(+)-glucopyranoside (B) and β-sitosterol were isolated from the roots (Tiwari and Yadav 1971). Alquinone, an anthraquinone (Yadav and Kalidhar 1994); stigmasterol; and emodin (1,6,8-trihydroxy-3-methylanthraquinone) (Husain et al. 2005) were isolated from the roots. Chatsiriwej et al. (2006) found that root cultures established from the high-anthraquinone-producing plants accumulated higher amounts of emodin and chrysophanol than those established from the low-anthraquinone-producing plants and leaves and roots of the intact plants.

Six phenolic compounds, five anthraquinones (rhein, aloe-emodin, emodin, chrysophanol and physcion) and a flavonoid (kaempferol) were isolated from C. alata roots (Fernand et al. 2008).

Various plant parts of Senna alata have multifarious pharmacological activities that include laxative, antimicrobial, antiinflammatory, antimutagenic, analgesic, choleretic, hypoglycaemic and hepatoprotective.

Methanol extracts of ten selected Nigerian medicinal plants including C. alata were found to contain steroids, terpenoids and cardiac glycosides, alkaloids, saponins, tannins and flavonoids (Akinmoladun et al. 2010). The highest amounts of total flavonoids were found in the leaf extracts of C. alata (275.16 μg/mL quercetin equivalent). The extract demonstrated significant antioxidant and radical scavenging activities, namely, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and hydroxyl radical scavenging activities, high lipid peroxidation inhibitory activity but low nitric oxide radical scavenging activity. The ethyl acetate extract of S. alata aerial parts was found to possess antioxidant properties as expressed by increase in antioxidant enzymes and the presence of phenolic compounds flavonoids naringin and apigenin (Okpuzor et al. 2009).

A refined C. alata leaf extract exhibited strong DPPH free radical scavenging activity with an IC₅₀ value of 2.27 μg/mL and showed no prooxidant activity in yeast, Saccharomyces cerevisiae (Saito et al. 2012). Three of its major components were shown to bind to DNA in vitro. One major component, identified as kaempferol-3-O-β-d-glucoside (astragalin), showed high affinity to DNA. The astragalin-DNA binding was found to occur through interaction with G–C base pairs, possibly by intercalation stabilized by H-bond formation.

Cassia alata and Cassia podocarpa have identical laxative potency and were the most likely candidates for laxative drug development in Nigeria (Elujoba et al. 1989). Senna alata leaves were found to have laxative effect and presumed to be due to active ingredient anthraquinones. In a multicentre randomized controlled clinical trial involving 80 adult patients with constipation, 28 patients were given at bedtime 120 mL of fluid with caramel colour, 28 administered mist. alba and 24 given Cassia alata infusion (Thamlikitkul et al. 1990). Eighteen per cent of patients in the placebo group passed stools within 24 hours, whereas 86 and 83 % of patients in mist. alba and Cassia alata groups, respectively, passed stools. The differences observed between placebo and mist. alba and placebo and Cassia alata were statistically highly significant. Minimal self-limited side effects, that is, nausea, dyspepsia, abdominal pain and diarrhoea, were noted in 16–25 % of the patients. Studies found Cassia alata fresh leaves showed significant purgative efficacy on volume and frequency in healthy subjects compared to placebo (Than et al. 2002).

In Thailand, Senna alata has been approved as a laxative drug in the Thai Herbal Pharmacopoeia 1998 and the Thai National List of Essential Drug 1999 (Panichayupakaranant and Intaraksa 2003). Hydroxyanthracene derivatives were demonstrated as the active constituents in this plant for the laxative property. The efficiency of herbal medicines depended on the plant raw material quality, which was usually related to the content of the active compounds. Recently, poor quality of S. alata leaves due to lower content of hydroxyanthracene derivatives relative to the standard value (i.e. not less than 1.0 % w/w of hydroxyanthracene derivatives, calculated as rhein-8-glucoside on a dried basis) had been a major problem in the production of the herbal medicines from S. alata. Studies found that the method and temperature of drying markedly affected the hydroxyanthracene derivative content. Drying of the leaves in a hot air oven at 50 °C gave a higher hydroxyanthracene derivative content (1.43 % w/w) than drying in a hot air oven at 80 °C (0.44 % w/w) or drying in the sun (0.95 % w/w). Study on the stability of hydroxyanthracene derivatives in C. alata leaf powder, which was kept in tight container at room temperature, found that the hydroxyanthracene derivative content did not decrease within 9 months.