Browsing by Author "Binuwangi, A. K. D. M."

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    Antioxidant activity and protein precipitating ability of peel extract of Nephelium lappaceum Linn. (Rambutan)
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Binuwangi, A. K. D. M.; Rajapakse, C. S. K.
    Nephelium lappaceum Linn. (Rambutan) peels, one of the tropical agricultural wastes, have been identified as a rich source of polyphenols with antioxidant properties. Plant phenolic compounds can interact with protein molecules and the polyphenol-protein complexes enhance the antioxidant capacity of polyphenols and therefore influences the bioaccessibility of phenolics. This study was aimed to determine the antioxidant activity and the bovine serum albumin (BSA) protein precipitating ability of peel extract of Rambutan (Nephelium lappaceum). Fresh Rambutan fruits of Malwana special variety were collected from a commercial cultivation in the Western province, Sri Lanka. Chemical constituents in dried, powdered Rambutan peels were extracted using cold extraction (extracting solvents = methanol, ethanol, and ethyl acetate) (6 days, 37° C) and methanolic soxhlet extraction (6 hrs, 60 °C) separately. Antioxidant activity and total phenolic content (TPC) of freeze-dried extracts were determined using 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay and Folin-Ciocalteu assay, respectively. The correlation between antioxidant activity and TPC was analyzed using Pearson’s correlation. Since the methanolic crude extract obtained from cold extraction was rich in phenolics, it was fractionated into hexane, dichloromethane (DCM), ethylacetate, and aqueous methanol, and their protein precipitation ability was determined using Bradford assay. Among the crude extracts, the highest percentage yield was obtained from soxhlet extraction (34.5 %). Methanolic cold extract had the highest TPC (332.56 ± 1.20 mg GAE / g of extract), and ethylacetate crude extract had the lowest TPC (210.13 ± 3.20 mg GAE / g of extract). Further, antioxidant activity of soxhlet extract (IC50 = 9.70 ± 0.50 µg/mL) and methanol (IC50 = 8.20 ± 0.35 µg/mL) and ethanol (IC50 = 8.31 ± 0.50 µg/mL) cold extract was significantly higher (p < 0.05) than that of synthetic antioxidant BHT (IC50=13.92 ± 1.19 µg/mL). Statistically significant (p < 0.01), a strong positive correlation was observed between DPPH radical scavenging activity and the TPC with Pearson’s correlation coefficient (r) of 0.99. Hence, the results suggested a potential for the utilization of peels N. lappaceum, as a nutraceutical enriched with natural antioxidants. According to results of protein precipitation potential of fractions, the highest percentage of BSA precipitate was observed (88.54 ± 0.92 %) in the ethyl acetate fraction. Thus, this study identified that Rambutan peel polyphenols have an affinity to bind with BSA at pH 4.5 in-vitro and the antioxidant activity of Rambutan peel extract would be masked by polyphenol–protein precipitation to some extent. Therefore, further studies should be necessary to isolate, purify, and identify polyphenols in Rambutan peels with their protein precipitation potentials to understand the mechanism of phenolic-protein interactions and their industrial applications.
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    Nephelium lappaceum L. peels as a source of phytochemicals with antioxidant and α-amylase inhibitory activities
    (Institute of Chemistry Ceylon Adamantane House, Rajagiriya, Sri Lanka., 2020) Binuwangi, A. K. D. M.; Rajapakse, C. S. K.
    Nephelium lappaceum L. (Rambutan) is a popular seasonal fruit native to Southeast Asia, enriched in varieties of phytochemicals including vitamins and secondary metabolites. This fruit is consumed fresh, canned, or as a processed food, but unfortunately its consumption results in production of vast amounts of waste from its seeds and peels which eventually create mosquito breeding grounds. Therefore, this study was conducted to investigate the potential of utilizing fruit waste (peels) of Sri Lankan variety of rambutan, Malwana special as a source of phytochemicals with antioxidant and α-amylase inhibitory activities. Phytochemicals of dried rambutan peels were first extracted into methanol by Soxhelt extraction. Then the crude extract was sequentially partitioned in hexane, dichloromethane (DCM) and methanol (30%). Total phenolic content (TPC) and total flavonoid content (TFC) of methanol extracts of rambutan peels and its fractions were determined using Folin- Ciocalteu and aluminium chloride method, respectively. Among the fractions, the highest TPC of 141.73 ± 18.66 mg gallic acid equivalents/g dried weight was found to be in aqueous methanol fraction and the DCM and aqueous methanol fractions were rich in flavonoids with TFC of 136.41 ± 32.25, and 110.67 ± 1.43 mg quercetin equivalents/g dried weight, respectively. Further, the radical scavenging properties of all the fractions were investigated using 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay and their correlations with phenolics and flavonoids were analyzed using Pearson’s correlation. The methanol extract of peels (IC50 = 9.70 ± 0.50 μg/mL) and its aqueous methanol fraction (IC50 = 12.04 ± 0.80 μg/mL) showed higher DPPH radical scavenging activity than that of the control, butylated hydroxytoluene (IC50 = 13.92 ± 1.19 μg/mL). Strong positive correlations were observed between the antioxidant activity and the TPC and TFC with Pearson’s correlation coefficients of 0.9018 and 0.8493, respectively. Interestingly, it was also found out that the in vitro α-amylase inhibitory activity of the aqueous methanol fraction of the peels (IC50=75.17 ± 3.40 μg/mL) was significantly higher than the standard drug acarbose (IC50=171.5 ± 8.50 μg/mL). Results revealed that the peels of Sri Lankan variety of rambutan, Malwana special is a potential source of phytochemicals with antioxidants and α- amylase inhibitory properties.