Abstract: Rambutan (Nephelium lappaceum L.) is exotic fruit commonly found in South East Asia region such as Indonesia, Malaysia and Thailand. Some physico-chemical properties have been used to describe the characteristics of rambutan fruit, either edible part or nonedible one. The seed and peel of rambutan are considered as wastes, therefore, some scientists have attracted to investigate the biological activities of seed and peel to seek the possibility of both to be developed as functional food. Several biological activities, which are beneficial to human health are reported in rambutan fruit, namely antioxidant, antibacterial, antidiabetic and anticancer. The active components contained in rambutan such as ellagic acid, corilagin and geraniin are responsible for those activities. This review highlighted some physico-chemical properties and the active compounds present in the fruit, seed and peel of rambutan along with the biological activities supporting rambutan fruit as functional food.
INTRODUCTION
Rambutan (Nephelium lappaceum L.), family of Sapindaceae is important tropical fruit in Southeast Asian region, especially in Indonesia, Thailand and Malaysia. Rambutan is a tropical plant which grown in warm, humid and low evaporation rates with high rainfall. Rambutan fruit is ovoid with a red or yellow pericarp. It is covered with soft spines and varied in color from green, yellow and red1. In Indonesia, there are some cultivars of rambutan with different characteristics, namely Rapiah, Narmada, Sinyonya, Binjai, Garuda, Kapulasan, lebak bulus, Si Batuk Ganal, Antalagi, Tangkue Lebak, Simacan, Bahrang and Sibongkok. Commercially, rambutan fruit is available as fruit fresh, juice, jam, marmalades and jellies2. In Indonesia, rambutan has some local names, namely Rambot in Aceh, Barangkasa in Maluku, Buiuwan in Bali, Rambuta in West Nusa, Balatung, Boeol, Rambusa Bolotu and Wulangas in Sulawesi, Banamon, Beliti, Bengayu, Beriti, Kayokan, Maliti, Puson, rambutan, Sagalong, Sanggalong and Siban in Kalimantan, rambuten in Sumatra, as well as rambutan in Java, Minangkabau and Madurese3.
The anatomical characteristics of whole rambutan fruit constitutes of 27.4% of weight, 13.2% peel, 11.7% pulp, 2.53% seed and 1.60% embryo4. Rambutan fruit is consumed freshly, consequently it produces huge amount of wastes from peel and seed. Therefore, it is important to take advantages of rambutan waste or underutilized part by exploring them for industrial purposes5. Besides nutritional aspects, rambutan may be contaminated with bacteria. Rambutan fruit cultivar Binjai is reported to contain endophytic bacteria from genus of Corynebacterium, Bacillus, Chryseobacterium, Staphylococcus and Curtobacterium. These bacteria are suspected to play as plant growth-promoting bacteria6.
CHARACTERIZATION AND COMPOSITIONAL ANALYSIS OF RAMBUTAN FRUIT
Rambutan fruit is potential to be used as functional food due to its capability to provide beneficial health effects. Underutilized part of rambutan (peel and seed) contain some active components which are reported to prevent some diseases, therefore the compositional analysis and its characterization of rambutan are explored by some plant scientists.
Chemical composition of rambutan fruit: Ong et al.7 have determined some volatile compounds (odor-active compounds) in rambutan fruit using gas chromatography-flactometry (GC/O) and gas chromatography-mass spectrometry (GC/MS). The extraction solvents used are ethyl acetate (semipolar) and Freon (nonpolar) to obtain polar and nonpolar fractions of volatile compounds. The polar fraction contained more odor-active compounds than nonpolar fraction.
The volatile compounds identified in rambutan fruit using GC/O are β-damascenone, (E)-4,5-epoxy-(E)-2-decenal, vanillin, (E)-2-nonenal, phenylacetic acid, cinnamic acid, ethyl 2-methylbutyrate, δ-decalactone, 3-phenylpropionic acid, 2,6-nonadienal, furaneol, 2-phenylethanol, m-cresol, maltol, heptanoic acid, nonanal, guaiacol, (Z)-2-nonenal and γ-nonalactone. Some other volatile compounds identified are (E,E)-2,4-decadienal, ethyl cinnamate, 2-acetyl-2-thiazoline, (E)-furan linalool oxide, carvone, (E,Z)-2,4-nonadienal, 1-octen-3-ol, γ-decalactone, (E,E)-2,4-nonadienal, furfural, benzothiazole, (E,Z)-2,4-decadienal, γ-undecalactone, 3-methyl(thio)propanol, endo-isocamphone, α-humulene, 2-heptanone, isoamyl acetate, 2-amylfuran, 2-methylbutyric acid, 2-acetylthiazole, ethyl butyrate, hexanal, hexanoic acid, hexyl acetate, 5-methylfurfural, isobutyl acetate, 1,2-dimethoxybenzene, isobutyric acid, octanoic acid, butyric acid, butyl acetate, ethyl crotonate, (E)-2-hexenal, (E)-2-hexen-1-ol, 1-hexanol, γ-butyrolactone, amyl acetate, ethyl 3-hydroxybutyrate, benzaldehyde, ethyl 3-hydroxy-3-methylbutyrate, ethyl hexanoate, benzyl alcohol, limonene, acetophenone, ethyl 2-hydroxycaporate, camphor-L, 2,3-dihydroxy-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one, benzyl acetate, octyl acetate, ethyl benzoate, (Z)-pyran linalool oxide, nonyl alcohol, (E)-pyran linalool oxide, benzoic acid, ethyl phenyl acetate and phenyl ethyl acetate3,7.
Chemical composition of rambutan seed: Rambutan seed is reported to contain proximate composition with moisture content of 9.6±3.52%, crude protein as determined using Kjeldahl of 7.6±0.14%, crude fiber 2.4±0.32%, lipid extracted using Soxhlet with petroleum ether as extracting solvent of 38.0±4.36%, carbohydrate (by difference) 28.7±0.43% and ash content of 1.22-2.26%8,9. Rambutan seed can produce a solid pleasant scented rambutan tallow which is similar to cocoa-butter. When heated, the fats obtained can be used as alternative sources in the cosmetics industry and biodiesels3,10, as substitute for cocoa butter due to the similar physicochemical characteristics between rambutan fat and cocoa butter11. Rambutan Seed Fat (RSF) contained some minerals needed by human, namely chromium (0.55 mg/100 g), manganese (1.62 mg/100 g), nickel (0.24 mg/100 g), copper (0.83 mg/100 g), zinc (40.61 mg/100 g) and and iron (24.77 mg/100 g)9.
| Table 1: | Physico-chemical properties of rambutan seed fat |
| -: Indicated no reported data | |
Lourith et al.12 have extracted fats from rambutan seed intended for industrial scale and found that maceration extraction technique using n-hexane for 1 h is the feasible means among other techniques. The extraction yield obtained is 30.12±0.04%. Re-use of n-hexane during maceration gave non-significantly different extractive yields (p>0.05). The main fatty acids present in RSF is oleic acid (C18:0) and arachidic acid (C20:0). Table 1 compiled fatty acid composition of RSF along with other physicochemical parameters. Rambutan seed is also potential source of flour which is rich in carbohydrate. The defatted rambutan seed flour can be obtained using supercritical extraction with CO2 at 35 MPa and 45̊C13. The seed flour is treated with alkaline solution and is compared with that of non-treated. During alkaline treatment, protein, fat and amylose contents are reduced with 9.1, 24.9 and 6.0%, respectively. The ash content of alkali-treated flour was higher than that of untreated flour (p<0.05).
Some chemical compounds are contained in rambutan seed. Ragasa et al.17 reported that dichloromethane extracts of rambutan seed contained two new diastereomeric monoterpene lactones (1) and (2), the known butenolide siphonodin (3) and kaempferol 3-O-β-D-glucopyranoside-7- O-β-L-rhamnopyranoside (4). The chemical structures of (1)-(4) are shown in Fig. 1.
Physicochemical composition of rambutan peel: The ethanolic extract of Rambutan Peel (RP) is reported to contain ellagic acid, corilagin and geraniin which are responsible for some biological activities. The methanolic and ethanolic extract of RP contain geraniin constituting of 56.8 and 37.9 mg g–1, respectively18,19. Liang et al.20 have isolated five oleane-type triterpene oligoglycosides from RP, namely hederagenin 3-O-(3-O-acetyl-β-D-xylopyranosyl)-(1→3)-α-L-arabinopyranosidealong (new compound) with four known compounds of hederagenin, hederagenin 3-O-(4-O-acetyl-α-L-arabinopyranosyl)-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside, hederagenin 3-O-α-L-arabinopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside and hederagenin 3-O-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→4)-β-D-xylopyranoside.
BIOLOGICAL ACTIVITIES OF RAMBUTAN FRUIT
Some biological activities of rambutan fruit along with its by-products (seed and peel) are reported such as antioxidant, antibacterial, antidiabetic and cytotoxic activity. These activities are deduced from several active compounds which include anthocyanins, phenolics and flavonoids. Some attempts have been made to isolate these bioactive compounds as much as possible, using experimental design approach. Maran et al.21 used central composite design using 4 factors (extraction temperature, extraction time, power of ultrasound and solid-liquid ratio) each with three levels. The optimal conditions based on both individual and combination of factors are achieved using extraction temperature of 50̊C, ultrasound power of 20 W, extraction time of 20 min and ratio solid-liquid of 1:18.6 g mL–1.
The safety evaluation of rambutan peel extract in male Wistar rats through acute and sub-chronic toxicities has been reported by Thinkratok et al.22. The acute toxicity is monitored by giving rats with single doses of extract. During acute toxicity, the serum levels of triglyceride (TG), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) remain constant. The LD50 was reported to be greater than 5000 mg kg–1 of extract.
| Fig. 1: | Chemical structures of two new diastereomeric monoterpene lactones, 1 and 2 and the known butenolide siphonodin (3), kaempferol 3-O-β-D-glucopyranoside-7-O-β-L-rhamnopyranoside (4), contained in rambutan seed |
The sub chronic toxicity is evaluated by administraion of extract into rats orally at doses of 500, 1000 and 2000 mg kg–1 daily for 30 days. During sub-chronic toxicitytest, there are no mortal rats found up to 1000 mg kg–1 day–1 of extract, while rats treated with extract at dose 2000 mg kg–1 day–1 exhibited the rat’s mortality of 12.5%. All the given doses of extract significantly decreased the levels of TG and blood urea nitrogen (p<0.05), but did not alter those of AST and ALT (p>0.05). The acute and sub-chronic toxicity studies of ethanolic extract of rambutan peel were also performed by Subramaniam et al.23. The results indicated that extract do not show rat’s mortality and no significant adverse effects observed, as indicated by no significant difference of some biochemical parameters of serum urea, ALP, AST, protein and total protein. The lethal dose of extract reported is >2000 mg kg–1, therefore, the ethanolic extract of rambutan peel is considered as not toxic. Rajasekaran et al.24 reported that methanolic extracts of raw seed, boiled seed and roasted seed of rambutan are safe up to 2.5 g kg–1 dose during acutetoxicity study.
Antioxidant anti-inflammation activities: Antioxidant activities of Rambutan Peel (RP) and by products are reported using some mechanisms including antiradical, ferric reducing activity, chelating agent, beta-chelating agent and lipid peroxidation method in vitro, as reviewed by Carocho et al.25 and Embuscado26. The antioxidant activities of rambutan are correlated with the presence of phytochemicals such as phenolics, flavonoids and carotenoids27,28. Permatasari and Rohman29 reported that ethanolic extract of RP from cultivars Simacam and Lebak bolus revealed strong antiradical activities toward 2,2’-diphenil-1-picrylhydrazil radical (DPPH). Among extracts and fractions evaluated, ethyl acetate fraction of RP cult. Lebak bolus has the highest antiradical activity with IC50 value of 2.732 μg mL–1, lower than that of positive control of vitamin C with IC50 of 1.998 μg mL–1. The correlation between IC50 and phenolics content revealed R2 of 0.594, while R2 for the relationship between IC50 and flavonoid content is 0.323. These correlations indicated that phenolics and flavonoid contents contributed to 59.4 and 32.30% of antiradical scavenging activity of RP extracts, respectively. Rohman et al.30 also investigated antiradical activities of extract and fractions of RP from two cultivars of Aceh and Binjai. Both cultivars revealed strong antiradical activities toward DPPH and 2,2-azinobis(3-ethylbenzo thiazoline-6-sulphonic acid) diammonium salt (ABTS). Thitilertdecha et al.31 have investigated the extracts of ether, methanol and aqueous of RP using DPPH radicals and the IC50 values reported are 17.3±1.03, 4.94±0.26 and 9.67±0.87 μg mL–1, repectively. The DPPH radical scavenging activity of the lyophilized water extract of peel, seed and pulp of rambutan cult. Seeechompoo and Rongrien revealed IC50 values in the range32 of 1.42-4.75 mg mL–1. Palanisamy et al.33 have compared DPPH radical activities of fruit pulp, seed, rind and leaves of rambutan. The ethanolic extracts of rind and leaves of rambutan exhibited the highest DPPH radical-scavenging ability. Using ABTS radical assay, ethyl acetate extract of RP showed the highest radical capacity with Trolox Equivalent Antioxidant Capacity (TEAC)34 of 23.0 mM mg–1. While, Tachakittirungrod et al.35 reported that ethanolic crude extract of RP has TEAC of 3.07±0.003 mM mg–1.
Using Ferric Reducing Assay Power (FRAP), the methanolic extract of RP revealed the highest activity with effective concentration (EC50) value of 20.2 mM mg–1 among extracts and fractions evaluated. The FRAP activities are correlated with phenolic contents34. The FRAP method is also used to evaluate the antioxidant activities of hexane, ethyl acetate and ethanol extracts of RP from 4 cultivars (Lebak bulus, Rajah, Rapiah and Binjai). The ethyl acetate extract of RP cult. Binjai showed the highest FRAP capacity with EC50 value36 of 77.1 μg mL–1.
The binary extraction system using the mixture of ethanol and water of RP was investigated for antioxidant assay in vivo. The oral administration of RP extracts into Sprague Dawley rats for 14 and 30 days resulted in a significant increase of antioxidant enzymes (superoxide dismutase, glutathione reductase and catalase), compared with those in control group rats37. Chingsuwanrote et al.38 have investigated antioxidant activity of rambutan cultivars Rongrien and Sichompu in vivo. The ethanolic extract of rambutan pulp cultivar Sichompu at 40 mg mL–1 is able to inhibit the formation of Reactive Oxygen Species (ROS) by 25% using pre-treatment of non-differentiated U937 cells, while rambutan cultivar Rongrien do not show significant antioxidant activity.
The radical scavenging activities of hexane, ethyl acetate and ethanol extracts of Rambutan Leaves (RL) from five cultivars namely Rapiah, Rajah, Binjai, Lebak bulus and non-edible rambutan using DPPH and ABTS were reported by Fidrianny et al.39. The ethanolic extract of RL cultivar Rapiah had the highest antiradical activities with IC50 value of 14.66 μg mL–1 (using DPPH) and IC50 of 12.826 μg mL–1 (ABTS). A correlation between these antiradical activities of all extracts studied and phenolics contents resulted R2 of >0.957. The un-blanched and blanched water extract of RL have similar antiradical activity toward DPPH radical with IC50 values of about40 1.00 μg mL–1. The rind and leaves also revealed the antiradical activity toward ABTS radical with IC50 values of 1.7±0.1 and 12.2±0.2 μg mL–1, respectively.
Chingsuwanrote et al.38 have evaluated anti-inflammation activity of rambutan cultivars Rongrien and Sichompu in vivo. The ethanolic extract of both cultivars inhibited the secretion of TNF-α, but not IL-8. This activity is deduced due to antioxidant activity of active compounds contained in all parts of rambutan.
Antibacterial activity: The activity of ether, methanol and aqueous extracts of RP in inhibiting some bacteria is reported by Thitilertdecha et al.31. The methanolic extract revealed the antibacterial activity against five pathogenic bacteria, namely Pseudomonas aeruginosa with Minimum Inhibition Concentration (MIC) of 62.5 mg mL–1, Vibrio cholera and Enterococcus faecalis, each with MIC of 15.6 mg mL–1, Staphylococcus aureus with MIC of 31.2 mg mL–1 and Staphylococcus epidermidis with MIC of 2.0 mg mL–1.
The water extract of rambutan seed is also tested for antibacterial activity using the disc diffusion method against pathogenic bacteria, namely Staphylococcus aureus, Streptococcus pyogenes, Bacilllus subtillis (representative Gram positive bacteria), as well as Escherichia coli and Pseudomonas aeruginosa (representative Gram negative bacteria). The inhibition zones of S. pyogenes, B. subtilis, S. aureus, E. coli and P. aeruginosa are 12±0.10, 12±0.40, 13±0.80, 6.5±0.66 and 10±0.55 mm, respectively. The positive control of antibiotics (Kanamycin) revealed inhibition zones on 28, 21, 26.5, 20 and 25 mm toward these five bacteria, respectively41. Rajasekaran et al.24reported that methanolic extracts of raw seed and boiled seed of rambutan are very sensitive toward Staphylococcus epidermidis with MIC value of 40 g mL–1. Ragasa et al.17 reported that dichloromethane extracts of rambutan seed contained two new diastereomeric monoterpene lactones, 1 and 2 which exhibited antibacterial activities.
Antidiabetic activity: Soeng et al.42 have evaluated antidiabetic effect of ethanolic extract of RP and its fraction in vitro based on inhibition of α-glucosidase. Alpha-glucosidase is an enzyme involved in the digestion and absorption of carbohydrate. Among ethanolic extract and its fraction (n-hexane, water, ethyl acetate, butanol), ethanolic extract has the highest antidiabetic activity with IC50 9.92 μg mL–1. The ethanolic extract of RP is also reported to have antidiabetic activity on alloxan-induced diabetic male Albino rats with dose of 0.45 mg kg–1 b.wt. The highest percentage reduction in blood glucose levels were shown of rambutan fruit peels extract with dose 500 mg kg–1 b.wt. and the percentage reduction of glucose was 61.76±4.26%43. Geraniin, isolated from RP using HPLC is evaluated for its capability to reduce glucose levels in male Sprague Dawley (SD) rats given by high-fat diet pellets. There is a significant decrease in plasma glucose levels of rats treated with geraniin compared to high fat diet rats (rat controls). This result supported that RP has been potential to be used for antidiabetic patient44.
Palanisamy et al.45 reported that aqueous extract of RP has antidiabetic activity by regenerating functional pancreatic beta cells and consequently reducing the glucose levels (hypoglycemic activity). This extract showed the inhibition effect toward carbohydrate hydrolyzing enzymes, such as α-glucosidase with EC50 (effective concentration capable of inhibiting 50% enzymes) of 2.7 μg mL–1 and α-amylase with EC50 of 70.8 μg mL–1. While, positive control of acarbose has EC50 of 3500 μg mL–1. Furthermore, the active component of geraniin contained in that extract is capable of inhibiting aldol reductase (EC50 of 0.04 μg mL–1) and preventing glycation end-products formation by 43%. The ethanolic extract of RP using geraniin as marker compound is also evaluated for its antidiabetic activity on male Sprague Dawley rats fed with high fat diet followed by injection with nicotinamide and streptozotocin to induce type 2 diabetes. Metformin was used as positive control. The results showed that the glucose levels in the diabetic rats treated with RP is reduced and insulin levels are improved. These effects are comparable to those of metformin-treated groups. The RP revealed anti-hyperglycaemic activity without any major toxic effects in high-fat diet induced diabetic rats46.
Anticancer activity: Rambutan fruit is reported to have anticancer activities through some mechanisms including cytotoxic effect, anti-proliferative and anticancer. Khonkarn et al.34 reported that hexane extract of RP has the cytotoxic activity toward KB cell line (human epidermal carcinoma of the mouth with HeLa contaminant) by MTT assay with IC50 of 7.7 mg mL–1 and no detectable cytotoxicity effects toward normal cells. The hexane fraction is supposed to contain novel active compounds with anticancer activity. However, the methanolic and water extracts of RP did not exhibit cytotoxic effects toward 4T1 (mouse breast cancer cell) and 3T3 cells (mouse embryonic fibroblasts cell) at doses47 of 50 and 100 μg mL–1.
The methanolic extracts of seeds and pericarps of rambutan are tested for cytotoxic activities against human mouth carcinoma (CLS-354) cells. Both extracts exhibited weak cytotoxicity against CLS-354 cells and reduced human Peripheral Blood Mononuclear Cells (PBMCs) viability. Due to its activities as antioxidant and cytotoxic effect, rambutan can be explored as chemo-preventive agents48. Hidayat et al.49 reported that ethanolic extract of RP has in vitro activity against human osteosarcoma cancer cells and had no effect on normal cells. The extract induced G2/M arrest via inhibition of cancer cell cycle progression.
CONCLUSION
Rambutan is tropical fruit having some biological activities. All parts of rambutan either edible part or nonedible parts have been reported to contain some components beneficial to human health such as geraniin, ellagic acid and corrilagin. Several activities are reported for rambutan fruit including antioxidant and anti-inflammation, antibacterial, antidiabetic and anticancer.
SIGNIFICANT STATEMENTS
| • | Rambutan is important fruit in tropical countries |
| • | The consumption of fresh rambutan fruit can produce huge amount of wastes from seed and peel |
| • | Seed and peel rambutan are potential to be developed as functional food |
| • | Some active components present in rambutan fruit like ellagic acid, corilagin and geraniin contribute to the beneficial biological activities toward human health |
ACKNOWLEDGMENT
The authors thanks to Faculty of Pharmacy for financial support during conducting research activity via sheme English Thesis Scheme.