Antioxidant, a-Amylase Inhibitory Activities and Photoprotective Properties of Peels of Nephelium Lappaceum Linn. (Malwana Special)

Introduction

Reactive oxygen species (ROS) in biological systems include superoxide (O₂^●-), hydroxyl (HO^●), singlet oxygen (¹O₂) and peroxyl (RO₂^●) radicals¹. Reactive oxygen species are generated as byproducts during oxidative metabolism in the mitochondrial electron-transport system and as intermediates in some enzymatic reactions¹. Besides,excessive exposure to UV radiation can also generate ROS in the skin².An imbalance between ROS and scavenging systems causes oxidative stress and consequently, leading to various chronic diseases including cancer, diabetes mellitus, and aging in humans³. Recent studies have shown the central role of antioxidants in mediating chronic diseases by inhibiting the formation of free radicals and terminating oxidative chain reactions⁴. However, the use of synthetic antioxidants has been questioned due to their possible carcinogenicity and instability⁵. Therefore, it is important to investigate efficient, safe, cost- effective and biologically active phytochemicals to replace synthetic bioactive compounds. Vitamins, phenolics, and carotenoids are three main groups of remarkable antioxidants in fruits and vegetables⁶ that are important for our health as they  guard the human body from ROS mediated disorders⁷.

Interestingly, not only the fruits and vegetables but also some of their  wastes such as peels, seeds, and pomace are known to enrich with many bioactive compounds⁸. Peels of fruits such as mango, grape, mangosteen, and avocado have been reported to contain higher amounts of bioactive compounds^8,9. Food wastes including fruit and vegetable wastes that end up in the landfills produce methane; a powerful greenhouse gas which affects the climate changes¹⁰. As the climate changes are posed serious threat to habitats of organisms, this eventually affect the biodiversity. Therefore, valorization of agro-food wastes by extracting valuable bioactive
compounds is a worthwhile strategy to minimize this problem.

Nephelium lappaceum Linn. (rambutan) belongs to family Sapinadaceae¹¹; closely related to litchi, longan, mangosteen, and durian¹². Rambutan is native to Southeast Asia.Three rambutan varieties are mainly cultivated in Sri Lanka. They are Malayan Red, Malayan Yellow, and Malwana special¹³.Among these, Malwana special is the most widely grown high-yielding variety¹² and it is famous in export market due to its excellent quality as a fresh fruit¹². Unfortunately during the fruit season, a vast amount of waste is generated from its peels which eventually create mosquito breeding grounds⁶. Efforts on value addition to peels of rambutan have led to the identification of powerful antioxidants particularly ellagitannins^14,15.

Ellagitannins have exhibited a greater activity than butylated hydroxytoluene (BHT) and vitamin E^14,16 which are also effective in inhibiting digestive enzymes¹⁷. Photoprotective efficacy of formulations containing crude extract of rambutan peel has also been recently reported¹⁸. Apart from the recent investigation on antioxidant and anti-inflammatory activity of aqueous extract of rambutan peels¹⁸,no studies have been focused on valorization of peels of rambutan variety, Malwana special.

Therefore, the aim of this research was to investigate the potential utilization of by-products (peels) of Nephelium lappaceum Linn., Malwana pecial, a common rambutan variety in Sri Lanka as a source of phytochemicals rich with antioxidant and α-amylase inhibitory activities and photoprotective properties.

Materials and Methods

Plant material

Fresh rambutan fruits of Malwana special variety were collected from a commercial cultivation in Western province, Sri Lanka in June  2019. The variety identification was done by the Fruit Research and Development Institute, Horana, Sri Lanka. The peels were removed, washed with tap water, cut into smaller pieces, soaked, and air-dried for 6 days. Dried peels were ground and packed in sealed polythene bags and then kept at 4 ⁰C until use.

Sample preparation

The chemical constituents in powdered rambutan peels (10.0 g) were extracted using a laboratory-scale soxhlet apparatus with 99% methanol (120.0 mL) for 6 h at 60 ⁰C until the solvent in the siphon tube become colorless. Then extract was filtered and solvent was removed using a rotary evaporator (IKA RV 10 digital, Germany) at 35 ⁰C and freeze-dried using a freeze dryer (LABCONCO, USA) and kept at 4 ^oC until further use.

Fractionation of methanol extract

Dried methanol crude extract was dissolved in methanol (50 mL) and transferred into 500 mL separatory funnel. Methanol extract was successively partitioned into hexane (40 mL). Resulted methanol layer was mixed with dichloromethane (DCM) (75 × 2 mL). Then 5 mL of distilled water was added to separate the DCM layer from aqueous methanol layer. Resulted fractions (hexane, DCM, aqueous methanol) were separately concentrated and freeze-driedand kept at 4 ⁰C until further use.

DPPH radical scavenging assay

The α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging assay was carried out by following the method reported by Chatatikun and Chiabchalard(2013)¹⁹ with slight modifications. 160 μL of various concentrations of the methanol extract, and its fractions (hexane, DCM, and aqueous methanol) and standard (BHT) (250, 125, 62.5, 31.25, 15.63, 7.82, 3.91, 1.95 μg/mL) were added to methanolic DPPH (40 μL,0.26 mg/mL). The absorbance was recorded at 517 nm using microplate spectrophotometer (Multiskan go 1.00.40, Thermo scientific) after incubating the well-mixed samples in the dark for 15 minutes. The control consisted of 160 µL of methanol and 40 µL of DPPH. The percentage inhibition (%) was calculated by using the equation 1;

where, A_c and A_s are the absorbance of the control and absorbance of the sample (extracts or standard) respectively. The sample concentration which generates 50% DPPH inhibition (IC₅₀) was determined by the plot of percent inhibition versus concentrations of the samples.

Total phenolic content (TPC)

The total polyphenolic content (TPC) in methanol extract of rambutan peels and its fractions were determined according to the Folin-Ciocalteau (F-C) method²⁰ with slight modifications. Briefly, 0.10 mL of sample solutions, (1000 μg/mL) (n = 3 each) were transferred to 7.9 mL of deionized water, and incubated with 0.5 mL of F–C reagent and 1.5 mL of 200 g/L Na₂CO₃ solution for 2 h. Then, absorbance was recorded using microplate spectrophotometer at 760 nm. TPCof each sample was calculated using the constructed Gallic acid standard curve (R² = 0.97).

Total flavonoid content (TFC)

The total flavonoid content (TFC) in the methanol extract and its fractions were determined by AlCl₃ colorimetric method with slight modifications²¹. Briefly, samples (0.5 mL, 1000 µg/mL)   (n = 3 each) were incubated with deionized water (2.0 mL) and 5% NaNO₂ (150 μL) for 5 minutes in the dark. Then 10% AlCl₃ (150 μL) was added and incubated for 6 minutes. Next, the absorbance of samples was recorded at 510 nm using microplate spectrophotometer after adding1 M NaOH (1.0 mL) and distilled water (1.0 mL) to the samples. The blank was prepared with all the reagents except peel extract. The same procedure was carried out for the standard concentration series of quercetin (1000, 800, 500, 400, 250, 200, 125 µg/mL) instead of the sample. TFC of each sample was determined by the constructed quercetin standard curve (R² = 0.98).

Determination of photoprotective properties

Chromatographic fractionation of aqueous methanol fraction

As theaqueous methanol fraction had the highest phenolic content and the highest DPPH free radical scavenging activity, it was selected to evaluate its photoprotective properties. Firstly, aqueous methanol fraction was purified using silica gel column (130×16 mm) by eluting the column with ethyl acetate (100%, 150 mL), ethyl acetate: acetone (1:1, 150 mL), acetone (100%, 200 mL) and ethanol (100%, 100 mL). According to similarities in thin layer chromatography (TLC) profiles of collected fractions, fractions were combined into 3 sub-fractions: Fraction-A (1-60 fractions), Fraction-B (61-80 fractions), and Fraction-C (81-132) and solvents were evaporated under reduced pressure and stored at 4 ^oC until further use. Further, UV spectra of three sub-fractions were recorded.

Determination of in vitrosun protection factor (SPF)

The estimated sun protection factor(SPF) of fraction-A was determinedby a  spectrophotometric method²², using the equation 2.A commercial sunscreen product containing Avobenzone 3.0%, Homosalate 10.0%, Octisalate 5.0 %, and Octocrylene 10.0% as active ingredients was selected as the references for this study. Fraction-A and the reference sunscreen were dissolved in methanol (99.8% from Sigma-Aldrich) to prepare solutions of 2.0 g/mL. A dilution series of the Fraction-A and reference sunscreen were prepared (0.03, 0.06, 0.13, 0.25, 0.5, 1 mg/mL). UV absorbance of each dilution was determined (n=3) from 290 to 320 nm (UV-B region in the spectrum), at 5 nm intervals using the microplate spectrophotometer. Methanol was used as the blank.

Where, CF = Correction factor (equal to 10). It was estimated from the standard formulation containing 8% homosalate with SPF of 4¹⁸. EE (λ) is the erythematogenic effect of radiation at the wavelength lI (λ) is the intensity of light at the wavelength λ; abs (λ) is the absorbance reading of plant extract or reference sunscreen at the wavelength λ. The values of EE × I were predetermined²³.

In vitro α-amylase inhibitory activity

The α-amylaseinhibitoryactivity of aqueous methanol fraction of rambutan peels was evaluated by the method reported¹⁷with few modifications. Briefly, the aqueous methanol fraction (80 µL, 7.81-1000 µg/mL) of peel of rambutan, starch (40 µL, 1%, w/v), and amylase in phosphate buffer (40 µL) were incubated at 37 ⁰C for 10 min. Next, dinitrosalicylic (DNS) reagent (80 µL) was added and incubated at 95 ⁰C for another 10 min. Reaction mixtures were cooled and the absorbances were measured at 540 nm. Acarbose (125-1000 µg/mL) was used as the positive control. Sample blanks were prepared by replacing the enzyme with the buffer. For negative control, deionized water was used instead of plant extract. For blank solution of the negative control, distilled water and buffer was used instead of plant extract and enzyme. The α-amylase inhibitory activity was given as percentage inhibition and it was calculated using the equation 3;

where, A _neg.control is the absorbance of the negative control. A _blank is the absorbance of the blank. A _sample is the absorbance of samples containing plant extract/positive control. A _{sample blank} is the absorbance of sample blank. The half maximal inhibitory concentrations (IC₅₀) were obtained by plotting % α-amylase inhibition against concentration of extract/standard.

Statistical analysis

All the experiments were conducted in triplicate. The results were processed statistically using GraphPad Prism 7.00 Statistic software.All data were reported as mean ± SD. Significant differences were assessed from Tukey’s pairwise test after conducting ANOVA⁵.Values were considered significant at p < 0.05. IC₅₀ values were obtained from GraphPad prism software by non-linear regression analysis program. Pearson’s correlation analysis was performed among 1/IC₅₀ and TPC or TFC.

Results and Discussion

In vitro antioxidant activity: DPPH free radical scavenging activity

Most natural antioxidants are known to have similar or higher antioxidant capacities than synthetic antioxidants (e.g. BHT,2-3-ter-butyl-4-methoxyphenol (BHA), and ter-butylhydroquinone (TBHQ))²⁴. In the present study, DPPH radical scavenging assay was used to evaluate the antioxidant activity of the methanol extract of rambutan peels and its fractions. DPPH free radical has a deep violet color due to the delocalization of spare electron (λ _max = 517 nm)²⁵. In the presence of  an electron or hydrogen radical donor, DPPH converts into its diamagnetic reduced form leading to a color change from violet to yellow²⁶. Figure 1 illustrates the percentage inhibition of DPPH  vs. concentration of methanol extract and its fractions alongside positive control, BHT. IC₅₀ values of each fractions are given in Table 1.

Figure 1: DPPH radical scavenging activity (inhibition %) of methanol extract and its hexane, DCM and aqueous methanol fractions. BHT was used as the standard antioxidant (n=3). Click here to View figure

According to the Figure 1, methanol extract and all of its fractions exhibited DPPH radical scavenging activity. Among the fractions, aqueous methanol fraction exhibited the highest radical scavenging activity with the highest percent inhibition ranging from 18.4 to 87.5% for concentrations from 3.9 to 150 µg/mL. The positive control, BHT, showed values of 13.2 – 84.3% for the same concentration range. Further, methanol extract, DCM fraction, and aqueous methanol fraction reached to >80% of DPPH radical scavenging activity at the concentration range 50-100 µg/mL.

Table 1: IC₅₀ values of the methanol extract of rambutan peels and its fractions.

IC50 values ( µg/mL )
BHT	methanol extract	hexane fraction	DCM fraction	aqueous methanol fraction
13.92 ± 1.19c	9.70 ± 0.50d	69.10 ± 1.08a	20.81 ± 0.21b	12.04 ± 0.80c

Values are mean ± standard deviation.Different letters (a–d) within the row differs significantly (p < 0.05).

The IC₅₀ of methanol extract exhibited a significantly (p < 0.05) higher radical scavenging activity than BHT. There was a significant difference (p < 0.05) between IC₅₀ values of methanol extract and its fractions (Table 1). Among the fractions, aqueous methanol fraction had the lowest IC₅₀ followed by the DCM  and hexane  fractions respectively.

Total phenolic content (TPC) and total flavonoid content (TFC)

High antioxidant activity of many fruits and their wastes are associated with phenolic compounds. Flavonoids are reported as one of the most important natural phenolic compounds with various biological and chemical activities²⁷. TPC and TFC of methanol extract of rambutan peels and its fractions with their corresponding yields are presented in Table 2.

Table 2: Mean values ofyield, total polyphenolic content, and total flavonoid content of methanol extract of rambutan peels and its fractions.

Extract/fraction	Yield (g)	TPC*	TFC*
Methanol extract Hexane fraction DCM fraction Aqueous methanol fraction	3.45 0.04 0.13 2.38	318.59 ± 0.09a 38.80 ± 0.16b 103.89 ± 0.51c 141.73 ± 18.66d	245.39 ± 4.83a 40.98 ± 4.17b 136.41 ± 32.25c 110.67 ± 1.43c

*Total phenolic content (TPC) is expressed in mg Gallic acid equivalents / g of dry weight of extract. Total flavonoid content (TFC) is expressed in mg quercetin equivalents / g of dry weight of extract. Values are given as mean ± standard deviation. Different letters (a–d) within the same column indicate significant difference at p < 0.05.

TPC of methanol extract and its fractions obtained from linear regression equation of Gallic acid calibration curve (y = 0.989x + 0.057, R² = 0.97) and expressed in mg of gallic acid equivalents (GAE) / g of dry weight of extract. When considering the TPC of fractionated methanol extract (Table 2), there was a significant difference (p < 0.05) of phenolic content in 3 fractions. Phenolics have been retained preferably in the aqueous methanol layer (141.73 ± 18.66 mg GAE/ g of dry weight of extract) due to the polar nature of the phenolics. A considerable amount of phenolics have also been fractionated into DCM (103.89 ± 0.51 mg GAE/ g of dry weight of extract) from methanol extract. Studies on other varieties of rambutan have identified peel as a good source of natural antioxidants with high phenolic content^15,14,20.It is reported that TPC of peel of rambutan from Rongrien and Seechompoo cultivars increases during fruit development and the highest content (402 mg GAE/ g of dry extract) obtains at the harvest stage²⁰. Phenolic profiles of a particular variety of plants can be altered by geographical conditions, differences in cultivars, properties of soil, methods of extraction, and analysis^6,28. Studies on peels of different mango genotypes in Sri Lanka have also reported the influence of genotype on phenolic content²⁹.

The TFC of methanol extract and its fractions obtained from linear regression equation of quercetin calibration curve (y = 0.0009x + 0.110, R² = 0.98) and expressed in quercetin equivalents (QE) (Table 2). TFC in methanol extract was 245.39 ± 4.83 mg QE/g of dry extract. TFC of hexane, DCM, and aqueous methanol fractions were 40.98 ± 4.17 mg QE/g of dry weight of extract, 136.41 ± 32.25 mg QE/g of dry weight of extract, and 110.67 ± 1.43 mg QE/g of dry weight of extract respectively. There was no significant difference (p > 0.05) in TFC of DCM and aqueous methanol fraction; indicating that the peel of Malwana rambutan may contain moderately polar and highly polar flavonoids that retain in the DCM and aqueous methanol layer respectively. In line with our findings, a previous study has also reported that flavonoid content of aqueous extract of peel of Malwana rambutan was 375.0 ± 13.2 mg QE/g²⁹ of dried plant material. Therefore, the results confirmed that the peel of Malwana rambutan variety is enriched with flavonoids.

Correlation between TPC, TFC, and antioxidant activities

Strong positive correlations were observed between DPPH radical scavenging activity and the TPC and TFC with Pearson’s correlation coefficients (r) of 0.91 and 0.85 respectively(Table 3), suggesting that phenolic phytochemicals including flavonoids have contributed to strong antioxidant activity of the methanol extract of rambutan peels. Ellagitannins are the most active antioxidants identified from  methanol extract obtained from cold extraction of rambutan  peals in Thailand¹⁴. According to our knowledge, the current study was the first correlation study of TPC, TFC, and antioxidant activities of peels of Sri Lankan variety of rambutan; Malwana special.

Table 3: Statistical interpretation of the correlation of the TPC and TFC with the DPPH radical scavenging activity (1/IC₅₀).

Parameter*	1/IC50 vs. TPC	1/IC50 vs. TFC
Pearson correlation coefficient (r)	0.91	0.84
R2	0.83	0.71
p (two tailed)	<0.01	<0.01
Number of xy pairs	10	10

p < 0.01 indicates that correlation at the 0.01 level (two tailed) is significant (n=10). r: Pearson’s correlation coefficient. R²: regression values.

Photoprotective properties

The wavelength region of UV radiation is 100 nm – 400 nm and it is classified into 3 types, UV-A (λ = 320-400 nm), UV-B (λ = 290-320 nm), and UV-C (λ=100-290 nm). UV-B  radiation may induce skin aging and melanoma and non-melanoma skin cancers³⁰.UV-B radiation is considered as one of the  main causes of  skin damage leading to sunburn³¹. Recent studies suggested that phytochemicals in fruits such as green tea polyphenols and grape seed proanthocyanidins are efficient photoprotective agents³⁰. As a wide range of polyphenols were known to exhibit skin photoprotective properties, aqueous methanol fraction enriched with phenolics and flavonoids was tested for its photoprotective properties.Firstly, the aqueous methanol fraction of the rambutan peel extract was purified into 3 sub-fractions (Fraction A, B, C) using silica gel column chromatography.  According to UV spectra, Fraction-A, showed a broad absorbance peak (Figure 2(a)) near UV-B (280-315 nm) indicating the presence of chemical compounds with UV-B photoprotective properties.

Figure 2: UV spectra (200-400 nm) of partially purified aqueous methanol fraction, (a)  fraction- A, (b) fraction- B), (c) fraction- C Click here to View figure

The efficacy of UV-B protection of fraction-A was measured using an in vitro method, as it showed a significant correlation with data obtained in vivo²². The photoprotective properties of fraction-A and the reference were evaluated by determining sun protection factor (SPF) at different concentrations. The SPF can be defined as  measure of how well a sunscreen will protect skin from UV-B rays²³. According to results illustrated in Figure 3, both the fraction-A and reference exhibited photoprotective properties in dose dependent manner in the concentration range of 0.03-2 mg/mL. Studies have reported that efficacy of UV-filters in sunscreen depended on concentration of photoprotective agents²². According to the SPF ratings,² at the highest concentration tested (2.0 mg/mL), the reference and fraction-A possess high (SPF = 33.67 ± 0.04) and moderate (SPF = 25.00 ± 0.11) photoprotective properties respectively.

Figure 3: Sun protection factor (SPF) of fraction-A and the reference sunscreen product against concentration (mg/mL). Click here to View figure

Further, it has also been noted that the IC₅₀ (DPPH free radical scavenging activity) of fraction-A was 35.30 ± 1.32 µg/ mL, indicating that free radical scavenging activity of fraction-A adds a beneficial property to protect the skin from UV induced oxidative stress and DNA damage². Therefore, the results revealed that the yellowish fraction (fraction-A) isolated from aqueous methanol fraction has a potential to use in sunscreen products since adding antioxidants to UV filters in sunscreen has been identified as a novel photoprotective strategy³². According to our knowledge, this is the first study on in vitro photoprotective ability of peels of N. lappaceum, Malwana special along with its antioxidant activity.Therefore, the in vivo studies should be carried out to determine the efficacy and safety of these polyphenols to be applied as an active ingredient in cosmetic products.

a-Amylase Inhibitory Activity

Diabetes mellitus is one of the prevailing metabolic disorders characterized by high levels of blood glucose.α-amylase is responsible for hydrolyzing dietary starch mainly to maltose, prior to absorption as glucose. Inhibition of α-amylase activity result in slow down the hydrolysis of α-1,4-glycosidic bonds in starch and other oligosac charides into simple sugars³³ which  delays the glucose absorption. Thus, inhibition of α-amylase activity plays a vital role in the management of diabetes³⁴. Since natural products rich in polyphenols have been proposed as a potential source of nutraceutical for patients with diabetes³⁵, the aqueous methanol fraction which had the highest phenolic content  was assessed for in vitro α-amylase inhibitory ability. As shown in Figure 4, phenolic rich aqueous methanol fraction inhibited α-amylase (IC₅₀ = 75.17 ± 3.40 µg/mL) more effectively than the positive control acarbose (IC₅₀ = 171.50 ± 8.50 µg/mL)indicating that the extract contained bioactive compounds with potential α-amylase inhibitory activity. There is a synergistic act of different polyphenol compounds on different steps in starch digestion³⁶. High activity of the extract may be due to combination of several phenolic compounds. Previous studies on other varieties of rambutan have also reported the efficacy of peel extracts compared to acarbose¹⁷.

Figure 4: α-amylase inhibitory activity (%) of aqueous methanol fraction of peel of rambutan and acarbose. data are mean ± sd (n=3). Click here to View figure

Conclusion

The sequential fractionation of soxlet methanolic extract of peels of N. lappaceum, Malwana special into hexane, DCM and aqueous methanol revealed that phytochemicals with antioxidant activity have mainly concentrated into aqueous methanol fraction and showed the highest DPPH radical scavenging activity and it was greater than that of BHT. There is a clear potential for the utilization of peels N. lappaceum, Malwana special as a food additive enriched with antioxidants. It was also noted that the peels are rich in phenolic compounds including flavonoids.In vitro α-amylase inhibitory activity of the aqueous methanol fraction of the peels was significantly higher than the standard drug, acarbose suggesting its antidiabetic potential. Partially purified aqueous methanol fraction possessed moderate photo protective activity with SPF of 25.00 ± 0.11 compared to the reference sunscreen (SPF = 33.67 ± 0.04) at the sample concentration of 2.0 mg/mL. The synergistic act of UV-B protection with radical scavenging activity of phytochemicals present in peel of rumbutan can be considered as a promising  natural additive for enhancing photoprotective properties in sunscreen formulations.

Acknowledgement

The authors are grateful to the University of Kelaniya (RP/03/02/06/01/2018) and the National Science Foundation of Sri Lanka (RG/2013/EQ/01) for providing the necessary equipment and financial supports for this research work.

Conflict of Interest

The authors have no conflict of interest to declare.

References

1. Dayem, A. A.; Hossain, M. K.; Lee, S. B; Kim, K.; Saha, S. K.; Yang, G.; Choi, H. Y.; Cho, S. Int. J. Mol. Sci.2017, 18 (1), 1–21.
2. Stevanato, R.; Bertelle, M.; Fabris, S. Regul. Toxicol. Pharmacol.2014, 69 (1), 71–77.
   CrossRef
3. Russo, G.; Curcio, F.; Bulli, G.; Aran, L.; Della-morte, D.; Testa, G.; Cacciatore, F.; Bonaduce, D.; Abete, P. Clin. Interv. Aging.2012, 13, 757–772.
4. Tan, B. L.; Norhaizan, M. E.; Liew, W. P. P.; Rahman, H. S. Front. Pharmacol.2018, 9 (OCT), 1–28.
   CrossRef
5. Seneviratne, K. N.; Prasadani, W. C.; Jayawardena, B. Food Sci. Technol.2016,36 (4), 591–597.
   CrossRef
6. Nguyen, N. M. P.; Le, T. T.; Vissenaekens, H.; Gonzales, G. B.; Van Camp, J.; Smagghe, G.; Raes, K. Int. J. Food Sci. Technol.2019, 54 (4), 1169–1178.
   CrossRef
7. Del Rio, D.; Rodriguez-Mateos, A.; Spencer, J. P. E.; Tognolini, M.; Borges, G.; Crozier, A. Antioxid.Redox Signal.2013, 18 (14), 1818–1892.
   CrossRef
8. Cheok, C. Y.; Adzahan, N. M.; Rahman, R. A.; Abedin, N. H. Z.; Hussain, N.; Sulaiman, R.; Chong, G. H. Crit. Rev. Food Sci. Nutr.2018, 58 (3), 335–361.
9. Coman, V.; Teleky, B. E.; Mitrea, L.; Martău, G. A.; Szabo, K.; Călinoiu, L. F.; Vodnar, D. C. Adv. Food Nutr. Res.2020, 91 (1), 157–225.
   CrossRef
10. FAO . Food Wastage Footprint & Climate Change. 2015,
11. Wall, M. M.; Sivakumar, D.; Korsten, L. Rambutan (Nephelium Lappaceum L.). In Postharvest Biology and Technology of Tropical and Subtropical Fruits.; Woodhead Publishing Limited, 2011; 312–333.
    CrossRef
12. Edirimanna, E. R. S. P.; Rajapakse, R. G. A. S.; Premarathna, M. P. T.; Kahawaththa, K. J. P. K.; Kohombange, S.; Rathnayake, A. K.; Silva, K. R. C. d.; Dissanayake, D. C. K. K. Int. J. Hortic. Agric. Food Sci.2019, 3 (4), 211–215.
    CrossRef
13. https://www.doa.gov.lk/FCRDC/index.php/en/2015-09-22-05-59-43/63-rambutan-e (accessed Feb 7, 2021).
14. Thitilertdecha, N.; Teerawutgulrag, A.; Kilburn, J. D.; Rakariyatham, N. Molecules2010, 15 (3), 1453–1465.
    CrossRef
15. Hernández, C.; Ascacio-Valdés, J.; De la Garza, H.; Wong-Paz, J.; Aguilar, C. N.; Martínez-Ávila, G. C.; Castro-López, C.; Aguilera-Carbó, A. Asian Pac. J. Trop. Med.2017, 10 (12), 1201–1205.
    CrossRef
16. Muhtadi, M.; Haryoto, H.; Sujono, T. A.; Suhendi, A.; Yen, K. H. Med. Plants2014, 6 (1), 43–46.
    CrossRef
17. Palanisamy, U. D.; Ling, L. T.; Manaharan, T.; Appleton, D. Food Chem.2011, 127 (1), 21–27.
    CrossRef
18. Mota, M. D.; Morte, A. N.; Silva, L. C. R. C. E.; Chinalia, F.J. Photochem. Photobiol. B.2020, 205, 111837.
    CrossRef
19. Uduwela, U. D. H. K.; Deraniyagala, S. A.; Thiripuranathar, G. World J. Pharm. Res. 2019, 8 (2), 155. h
20. Chatatikun, M.; Chiabchalard, A. J. Chem. Pharm. Res.2013, 5 (4), 97–102.
21. Thitilertdecha, N.; Rakariyatham, N. Sci. Hortic. (Amsterdam).2011, 129 (2), 247–252.
    CrossRef
22. Silva, R. V.; Costa, S. C. C.; Branco, C. R. C.; Branco, A. Ind. Crops Prod.2016, 83, 509–514.
    CrossRef
23. Dutra, E. A.; Da Costa E Oliveira, D. A. G.; Kedor-Hackmann, E. R. M.; Miritello Santoro, M. I. R. Rev. Bras. Ciencias Farm. J. Pharm. Sci.2004, 40 (3), 381–385.
    CrossRef
24. Lourenço, S. C.; Moldão-Martins, M.; Alves, V. D. Molecules.2019, 24 (22), 14–16.
    CrossRef
25. Housam, H.; Warid, K.; Zaid, A. Int. j. pharm. pharm. sci.2015, 6, 441-444.
26. Karadag, A.; Ozcelik, B.; Saner, S. Food Anal. Methods.2009, 2 (1), 41–60.
    CrossRef
27. Panche, A. N.; Diwan, A. D.; Chandra, S. R. J. Nutr. Sci.2016, 5, 1-15.
    CrossRef
28. Padmini, S. M. P. C.; Samarasekera, R.; Pushpakumara, D. K. N. G. Trop. Agric. Res.2014,25 (2), 252-260.
    CrossRef
29. Kuganesan, A.; Thiripuranathar, G.; Navaratne A. N.; Paranagama, P. A. Int. J. Pharm. Sci. Res.2017, 8 (1), 70–78.
30. Nichols, J. A.; Katiyar, S. K. Arch. Dermatol. Res.2010, 302 (2), 71–83.
    CrossRef
31. Cefali, L. C.; Ataide, J. A.; Moriel, P.; Foglio, M. A.; Mazzola, P. G. Int. J. Cosmet. Sci.2016, 38 (4), 346–353.
    CrossRef
32. Shaath, N. A. Ultraviolet Filters. Photochem. Photobiol. Sci.2010, 9 (4), 464–469. https://doi.org/10.1039/b9pp00174c.
    CrossRef
33. Wickramaratne, M. N.; Punchihewa, J. C.; Wickramaratne, D. B. M. BMC Complement. Altern. Med.2016, 16 (1), 1–5.
    CrossRef
34. Arachchige, S. P. G.; Abeysekera, W. P. K. M.; Ratnasooriya, W. D. Evidence-based Complement. Altern. Med.2017, 2017, 1-13.
    CrossRef
35. Tundis, R.; Loizzo, M. R.; Menichini, F. Mini-Reviews Med. Chem.2010, 10 (4), 315–331.
    CrossRef

---

This work is licensed under a Creative Commons Attribution 4.0 International License.