Abstract
Nephelium lappaceum and its by-products have great potential in the agricultural, pharmaceutical, and food industries. Some studies have shown that N. lappaceum by-products exhibit antimicrobial, antioxidant, antidiabetic, and anticancer properties. However, studies focused on identifying these compounds are rare. The availability of polyphenolic compounds can vary according to environmental conditions, soil, plant variety, and agronomic management. Therefore, in this study, the active compounds in extracts of the N. lappaceum peel were identified, and their antioxidant properties were evaluated using various extraction solvents and both ultrasonic and boiling extraction techniques. The chemical characterization of the N. lappaceum peel exhibited carbohydrate and reducing sugar contents of 12 and 2%, respectively. Phytochemical analysis indicated the presence of flavonoids, tannins, terpenes, and steroids. The total phenolic and flavonoid contents and total antioxidant capacity were the highest in the hydroethanolic extract obtained by ultrasound, with values of 340 mg gallic acid equivalents g−1, 76 mg quercetin equivalents g−1, and 2.9 mmol of Trolox equivalents g−1, respectively. Contrarily, the total anthocyanin content was higher in the acid extract obtained by ultrasound, with a value of 0.7 mg cyanidin-3-O-glucoside equivalents g−1. A total of 18 compounds—including hydroxybenzene, phenolic acid, flavonoids, fatty acids (saturated, unsaturated, and ester), vitamin, arenecarbaldehyde, and phthalate—were identified for the first time in the N. lappaceum peel using gas chromatography-mass spectrometry. The identified compounds have been previously isolated from other plants and reportedly exhibit anticancer, anti-inflammatory, antimicrobial, and antioxidant activities. Thus, the N. lappaceum peel was shown to be a potential source of bioactive compounds of immense importance in the pharmacological and food industries.
Highlights
Nephelium lappaceum, known as rambutan, is a tropical fruit with excellent nutraceutical properties
The content of reducing sugars was determined from the absorbance of the cooled mixture at 540 nm, using a calibration curve prepared with glucose as a standard. e dinitrosalicylic acid (DNS) reagent was prepared by dissolving 0.748 g of DNS, 0.564 g of crystalline phenol, 21.612 g of Rochelle salt, 1.412 g of NaOH, and 0.564 g of sodium sulfite in 100 mL water. e total nitrogen concentration was determined by the Kjeldahl method (K415-K350-F308 Kjeldahl system, Buchi, Switzerland) according to AOAC Method 988.05 [45]. e phosphorus content was determined by the vanadomolybdophosphoric method described by Kitson and Mellon [46]
The N. lappaceum peel is an excellent source of essential elements such as nitrogen, calcium, potassium, phosphorus, magnesium, copper, zinc, manganese, sodium, and iron, as summarized in Table 2. ese elements are of considerable interest to the nutraceutical and food industries because they are crucial for the healthy functioning of the human body due to their roles in various vital processes such as cellular functioning, enzymatic activation, genetic expression, and bone and hemoglobin formation [52, 53]
Summary
Known as rambutan, is a tropical fruit with excellent nutraceutical properties. Erefore, in this study, we identified the active compounds present in the extract of the N. lappaceum peel and evaluated their antioxidant capacities using different extraction solvents (acid, alkaline, aqueous, ethanolic, and hydroethanolic) and both ultrasonic and boiling extraction techniques.
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