This synopsis updates the current knowledge on the ethno-cultural significance, phytochemical constituents and pharmacological properties of Mangifera pajang. In the Plant List of 2013, a total of 133 species of Mangifera have been listed of which only eight are accepted species names while the majority remains as unresolved names, including that of M. pajang.1 Unlike Mangifera indica (Indian mango) that is widely documented, there is only a book chapter on M. pajang,2 and a review on the fruits of M. pajang as a source of functional food and medicine.3 There are no reviews on the genus of Mangifera.
Mangifera pajang Kostermans of the family (Anacardiaceae) is endemic to the lowland rain forests of Borneo comprising Sabah, Sarawak, Brunei and Kalimantan.2-4 Commonly known as the Bornean mango, this endemic mango species is locally known as bambangan in Sabah and Brunei, mawang in Sarawak, and embang in Kalimantan. Growing more than 30 m tall, trees have a cylindrical bole (30-70 cm in diameter) with smooth or broadly fissured grey bark (Figure 1). Mature leaves are elliptic-oblong, coriaceous and dark green, while young leaves are bronze to pink.2 Flowers have five petals that are purplish-red on the inside and pinkish white on the outside (Figure 2).
Although growing wild in the forest, trees of M. pajang have been cultivated by the local Kadazan-Dusun people in Sabah.5 Currently, bambangan trees are planted in orchards and in the backyards of homes due to increasing demand for the fruits.
Weighing 0.5-1.0 kg each, fruits of M. pajang are among the largest in the genus.2,3,5 They are oval in shape, and have a characteristic rough and brown skin (Figure 2), unlike other Mangifera species which have a smooth, green, yellow, orange or red skin. During the fruiting season of bambangan (October to February), individual trees bear hundreds of fruits. The edible portion i.e. the pulp which represents 60-65% in total weight6 is aromatic, juicy, bright yellow in colour, sweet-sour in taste and fibrous in texture.7 The aroma is strongly that of M. indica (mango). The pulp of M. pajang fruits is usually eaten fresh after removing the peel and the kernel discarded.3 The peel, which is also aromatic, is sometimes used in cooking local dishes such as curry. In Sarawak, young leaves of M. pajang, sold in local markets, are blanched and consumed as vegetable with chilli and shrimp paste (sambal belacan) or fermented durian (tem-poyak).2
Fermented M. pajang fruits or jeruk bambangan is a popular food item among the Kadazan-Dusun community in Sabah.2,3 Fruits are cut into cubes with salt and grated kernel added, and left to ferment at 28-30°C in tightly-closed containers for 7-10 days. Available in most local markets and with a life-span of several weeks, the pickle is usually eaten with rice as an appetiser. Although fruiting of M. pajang is seasonal, the fermentation process makes the product available throughout the year. Lactic and citric acid are the major organic acids produced during fermentation.8 Main microorganisms involved are lactic acid bacteria of Lactobacillus plantarum and Pediococcus pentosaceus, and yeasts of Candida krusei and Kloeckera apis.
The most well-known traditional cuisine of the Kadazan-Dusun community in Sabah is hinava. (Figure 3), a salad-like dish consisting of pieces of raw fish marinated in lime or lemon juice and garnished with grated bambangan kernel, chilli, ginger and onion.2 Sometimes, slices of bitter gourd are added. Hinava is simple to prepare and yet its taste enriched with the aroma of bambangan is so exquisite that it leaves behind fond memories.
Extracts most of the phytochemical investigations on M. pajang are conducted on the fruits (Table 1). Flavonoids and phenolic acids are the two main classes of compounds found in the fruit peel, kernel and pulp. Selected flavonoids detected in the fruits of M. pajang are shown in Figure 3.
Flavonoids are widely distributed in plants and they constitute the largest group of phenolic compounds. They are 15-carbon compounds with a C6-C3-C6 skeleton consisting of two benzene rings which are connected by an oxygen-containing pyrene ring.17 As a group of compounds, flavonoids can be further divided into six major classes, namely, flavonols, flavones, flavanones, flavanols, anthocyanins and isoflavones. Phenolic acids are aromatic phenols with one carboxylic acid functionality and they consist of two groups, namely, hydroxybenzoic acids (HBAs) and
hydroxycinnamic acids (HCAs).17 HBAs have a C6-C1 structure that is derived from benzoic acid. Examples are p-hydroxybenzoic, protocatechuic, vanillic, syringic and gallic acids. HCAs have a C6-C3 structure that is derived from cinnamic acid. Examples are p-coumaric acid, caffeic acid, ferulic acid and sinapic acid.
The peel of M. pajang is rich in flavonoids (catechin, daidzein, diosmin, epicatechin, hesperidin, kaempferol, naringin, luteolin, morin, quercetin and rutin), and in phenolic acids (chlorogenic acid, p-coumaric acid, ellagic acid, ferulic acid, gallic acid, 4-hydroxybenzoic acid, protocatechuic acid, pyrogallic acid and vanillic acid).10,13,15 Dominant phenolic acids in the fruit peel are gallic acid (21 mg/g) and p-coumaric acid (13 mg/g).10 Aromatic esters, carotenoids and xanthophylls are also reported in the peel.9,11 Of particular interest is mangiferin found in the peel of M. pajang. Mangiferin or C-glycosyl xanthone is a natural xanthonoid that bears a catechol moiety and possesses an array of pharmacological properties such as antioxidant, anti-inflammatory, anti-diabetic, immunomodulatory, anti-tumour, antipyretic and neuroprotective activities.18,19 The mangiferin content of 4.8 mg/g in the peel of M. pajang10 is substantially higher than that in the peel (2.4 mg/g)18 and leaves (0.02.0.04 mg/g)19 of M. indica. Phenolic acids (caffeic acid, chlorogenic acid, p-coumaric acid, ferulic acid, gallic acid and sinapic acid), and flavonoids (diosmin, hesperidin, naringin and rutin) are detected in the kernel.15 Phytochemical analysis revealed the dominance of ferulic acid (5334 μg/g) and diosmin (2386 μg/g) in the kernel.5,15
From the edible pulp, flavonoids (daidzein, genistein, hesperidin, kaempferol, naringin, luteolin and quercetin), phenolic acids (caffeic acid, chlorogenic acid and p-coumaric acid), carotenoids (α-carotene and β-carotene), and xanthophylls (cryptoxanthin and cis-cryptoxan thin) have been reported.4,14 The pulp has 46 mg/100 g of ascorbic acid, 42 mg/100 g of p-carotene and 8.5 mg/100 g of daidzein.12,14 Naringin and hesperidin (Figure 3) are two major compounds of the fruit pulp of M. pajang with contents of 1450 and 930 |rg/g, respectively.15 In comparison with the bambangan fruit pulp, the fruit juice powder was three-fold higher (132 mg/100 g) in ascorbic acid content and comparable in p-carotene content (36 mg/100 g). A phytochemical analysis of the bambangan fruit juice showed the presence of gallic acid (1.7 mg/100 mL), vanillic acid (0.5 mg/100 mL) and trans-cinnamic acid (0.2 mg/100 mL).16
Apart from the fruits of M. pajang, little work has been done on the other plant parts (Table 1). From the leaves, methyl gallate, quercitrin, lupenone and lupeol, and from the stem bark, β-sitosterol, stigmasterol, mangiferonic acid, trans-sobrerol, lupeol, 3β,23-dihydroxy-cycloart-24-ene-26-oic acid and 3β-hydroxy-cycloart-24-ene-26-oic acid have been reported.9 Also reported in the leaves of M. indica,20 lupeol has anti-inflammatory and anti-arthritic properties.21 Polysaccharides from the fruit pulp extract of M. pajang have been isolated and separated into neutral and acidic components.22 The molecular weight of the neutral polysaccharide faction (F1) was 7 kDa while those of the acidic polysaccharide factions (F2, F3 and F4) were 13, 24 and 9 kDa, respectively. Major monosaccharide components were mannose, arabinose and glucose in F1 and F4; arabinose and rhamnose in F2; and glucose and fructose in F3.
A study on the proximate composition of 42 varieties of tropical fruits belonging to eight species reported that fruits of M. pajang had the lowest fat content of 0.2-0.4%.23 Protein and carbohydrate contents were 3.1-3.3% and 78-81%, respectively.
From the essential oil M. pajang fruits, 50 volatile components were identified7. Comprising mainly of monoterpene hydrocarbons (91%) and esters (7.6%), the two major components were a-pinene (67%) and a-phellandrene (11%). The kernel oil comprised 56%, 39% and 5.3% of saturated (SFA), mono-unsaturated (MUFA) and poly-unsaturated (PUFA) fatty acids.24 SFA contained 40% of stearic acid and 16% of palmitic acid while MUFA contained 39% of oleic acid. Low contents of linoleic acid (5.0%) and linolenic acid (0.4%) were detected in PUFA.
A study on the antioxidant properties of methanol extracts of M. pa-jang fruits reported the highest total phenolic content (TPC) and free radical scavenging (FRS) activity in the kernel.6 Compared to the peel and pulp, the TPC of the kernel was 4.5 and 17 times higher, while the FRS value of the kernel was 1.1 and 2.3 times stronger, respectively. Several recent studies have been conducted on the antioxidant properties of M. pajang. Kernel, stem bark and leaf extracts (petroleum ether, chloroform, ethyl acetate and methanol) and isolated compounds of M. pajang showed that ethyl acetate and methanol extracts of the kernel had the strongest FRS activity with IC50 values of 7.3 and 8.8 ug/mL, respectively.9 It was rightly noted that the kernel and peel as by-products of bambangan fruits have stronger antioxidant properties than the pulp.25 None of the stem bark extracts showed any FRS activity while only the ethyl acetate and methanol leaf extracts had weak activity. Isolated from the kernel and leaves of M. pajang, methyl gallate was the only compound with potent FRS activity of 6.24 ug/mL.
Compared to the fruits of six other wild Mangifera species, M. pajang ranked first in TPC and ascorbic acid content (AAC), but ranked poorly in FRS and ferric reducing ability.26 The values of TPC (7056 mg/100 g) and AAC (403 mg/100 g) of M. pajang were 56 and 3.2 times those of M. indica.
The antioxidant properties of fermented bambangan have been studied. Results showed that fermentation at elevated temperature of 35°C yielded higher contents of phenolic compounds and stronger antioxi-dant activities than fermentation at room temperature of 28°C.27 At 35°C, fermentation was faster and storage at 4°C was stable up to three months.
The study on the antioxidant properties of extracts and isolated compounds of M. pajang also tested their antimicrobial activity.9 Results showed that most of the extracts and isolated compounds did not show significant inhibition activity towards methicillin-resistant Staphylococ-cus aureus (MRSA), Pseudomonas aeruginosa, Salmonella choleraesuis and Bacillus subtilis. Interestingly, methyl gallate was the only compound that exhibited very strong antibacterial activity against MRSA with a diameter of inhibition zone (DIZ) of 22 mm, comparable to streptomycin with a DIZ of 23 mm. None of the extracts and isolated compounds displayed any antifungal activity against Candida albicans, Aspergillus ochraceus and Saccharomyces cerevisiae. Incidentally, methyl gallate isolated from the leaves of Anacardium occidentale (cashew) has also been reported to possess antibacterial activity.28 The compound displayed strong anti-quorum sensing against Gram-negative Chromobacterium violaceum by inhibiting violacein production.
The cytotoxic properties of M. pajang fruit extracts against human cancer cell lines have been reported. Only the kernel and peel extracts, but not the pulp extract, displayed cytotoxic effects.15 The extracts inhibited the proliferation of liver and ovarian cancer lines with IC50 values ranging from 35-92 ug/mL. The proliferation of colon cancer cell lines was inhibited only by the kernel extract (63 ug/mL). In a related study, the kernel ethanol extract of M. pajang was found to have cytotoxic effects on MCF-7 and MDA-MB-231 breast cancer cells with IC50 values of 23 and 31 ug/mL, respectively.29 Prior to apoptosis, the extract induced sub-G1 cell cycle arrest in MCF-7 cells and G2/M cell cycle arrest in MDA-MB-231 cells. Apoptosis involved caspase-2 and -3 in MCF-7 cells, and on caspase-2, -3 and -9 in MDA-MB-231 cells.
Recently, the cytotoxic properties of extracts and isolated compounds of M. pajang have been reported.9 Results showed that the kernel had the strongest activity followed by the stem bark and leaves. Extracts of the kernel that exhibited strong cytotoxic activity with IC50 values less than 10 ug/mL were methanol (MCF-7, HeLa and HT-29 cells) and ethyl acetate (MCF-7 and HeLa cells). Petroleum ether, chloroform and ethyl acetate extracts of the stem bark showed strong to moderate activity against MCF-7, HeLa and HT-29 cancer cell lines with IC50 values ranging from 5-30 ug/mL. Moderate activity was shown against MCF-7 cells by the methanol leaf extract, and the petroleum ether leaf extract weakly inhibited HeLa and HT-29 cells. The study also tested the cytotoxic activity of compounds isolated from M. pajang.9 Isolated from the stem bark, 3p-hydroxy-cycloart-24-ene-26-oic acid displayed the strongest activity against HeLa cells with an IC50 value of 6.3 ug/mL. Based on their cytotoxic activity, the compounds can be ranked as follows: 3p-hydroxy-cycloart-24-ene-26-oic acid > methyl gallate > mangiferonic acid > lupeol > lupenone.
The protective effects of the M. pajang ethanol fruit extracts against oxi-dative damage caused by tert-butyl hydroperoxide in the human hepato-cellular HepG2 cells have been investigated.30
Results showed that only the kernel extract and quercetin (positive control) displayed cytoprotective activity in HepG2 cells, with EC50 values of 1.2 and 5.3 ug/mL, respectively. Expression of glutathione reductase and methionine sulphoxide reductase A were significantly up-regulated by the extract, suggesting its involvement in cytoprotection.
The fruit juice of M. pajang has been reported to be rich in gallic acid (1.7 mg/100 mL), and possess strong antioxidant properties such as free radical scavenging, p-carotene bleaching, and inhibition of haemoglobin oxidation and low-density lipoprotein (LDL) oxidation.16 Daily supplementation of hypercholesterolemic rabbits with M. pajang fruit juice powder had positive effects on their cardiovascular biomarkers.31 At dosages of 5%, 15%, 25% and 35% of the fruit powder, plasma malo-ndialdeyde and hepatic malondialdeyde were significantly decreased. At 25%, the powder significantly decreased total cholesterol, triglycerides and LDL cholesterol by 37%, 67% and 30%, respectively. The animal experiment led to a clinical trial to test the health benefits of M. pajang fruit juice on plasma vitamins and antioxidant enzymes, and on the liver and kidney function of human subjects.32 Bambangan fruit juice in 250 mL bottles was produced from 50 g of fruit powder containing 66 mg of ascorbic acid and 18 mg of p-carotene. The clinical trial involved 32 healthy subjects (12 males and 20 females) aged 24-28 years from the Faculty of Medicine and Health Sciences of Universiti Putra Malaysia (UPM) in Serdang, Selangor, Malaysia. Compared with the placebo, consumption of 250 mL of the fruit juice daily for nine weeks significantly increased the concentration of plasma p-carotene and ascorbic acid. At week 4, the increase was 45% and 28%, respectively. In addition, there was significant improvement in the plasma total antioxidant status with liver and kidney functions unaffected. The study at UPM32 concluded that the consumption of M. pajang fruit juice resulted in a significant improvement in certain cardiovascular biochemical parameters, which can safeguard the risk of cardiovascular diseases.
In Sabah, M. pajang or bambangan has ethno-cultural significance and has become an iconic fruit among the Kadazan-Dusun people. The community has developed various traditional cuisines using fresh and preserved fruits. Phytochemical investigations showed that the pulp, peel and kernel of M. pajang fruits are rich in flavonoids and phenolic acids. Pharmacological research affirmed that bambangan fruits possess anti-oxidant, antibacterial, anticancer and cytoprotective properties. A clinical trial has demonstrated the health benefits of regular consumption of bambangan fruit juice. Since M. pajang only fruits once a year, there is great potential for developing commercial products such as fermented bambangan, fruit juice and freeze-dried fruits, which have a much longer lifespan. Traditional and functional food products from bambangan fruits are being developed in Sabah. Further research is needed on the pharmaceutical applications of by-products such as the fruit peel and kernel, which are abundant in supply following consumption of the pulp.