EFFICACY OF EDIBLE AND NON-EDIBLE PARTS OF GRAPEFRUITS (CitrusparadisiMACF.) ON BIOMARKERS OF METABOLIC SYNDROME IN MALE WISTAR RATS

Abstract

Grapefruit consumption is a well-known therapeutic approach to the management of obesity due to its natural diuretic and antioxidant properties. Evidence suggests that the presence of polyphenols in grapefruits may reduce risk of metabolic syndrome (MetSyn). However, scientific research on its efficacy as an affordable management approach to MetSyn is limited. Therefore, this study assessed the efficacy of edible and non-edible parts of two varieties of grapefruits on metabolic syndrome biomarkers in Wistar rats. The study was experimental in design involving two phases. Phase one: edible (pulps) and non-edible (peels, seeds) parts of freshly harvested white and pink grapefruits were sorted, pulverised and freeze-dried. Edible white (EW), non-edible white (NEW), edible pink (EP) and non-edible pink (NEP) parts were quantitatively analysed for phytochemicals (total phenols, flavonoids, tannins, alkaloids, saponins) and carotenoids using standard procedures. Antioxidant activities were determined using2, 2-DiPhenyl-1-PicrylHydrazyl radicals (DPPH) and Ferric Reducing Antioxidant Power (FRAP) assays. Phenols (cholorogenic, gallic and caffeic acids) and flavonoids (naringin, narirutin, narigenin) were quantified using HPLC. Phase two involved grouping adult male wistar rats (9-10 weeks old) into 10 groups of eight. Group 1(Negative control [NC]) received corn starch-rich diet, group 2 (positive control [PC]) and groups 3 to 10 received MetSyn-inducing diet for 12 weeks. Groups 3 to 6 diets were supplemented with 0.8gEW, 0.4gNEW, 0.6gEP and 0.3gNEP grapefruit powder delivering 0.032g polyphenols while groups 7 to 10 had 1.6gEW, 0.8gNEW, 1.2gEP and 0.6gNEP supplying 0.064g polyphenols daily for eight weeks, respectively. Blood pressure (BP) was determined. Blood samples were analysed for lipid profile (total cholesterol, triglyceride, low-density lipoprotein, high-density lipoprotein), insulin resistance (IR),tumor necrosis factor-α (TNF-α), interleukin-6 and malondialdehydeusing standard procedures. Data were analysed using ANOVA at α0.05. Highest total phenols (111.1±0.5 mg GAE/g), flavonoids (25.3±0.1 mg QE/g), tannin (351.0±9.6 mg TAE/g), saponins (9.8±0.1 mg DE/g) and carotenoids (22.9±0.1 mg β-carotene equivalent/g) were obtained in NEP variety. Highest total alkaloids (2.9±0.1 mg AE/g) was obtained in EW variety. The antioxidant activity ranged from 26.6 to 79.2% for DPPH and 1.0 to 9.4 mM for FRAP in NEP and EW, respectively. Chlorogenic acid (117.2±2.3 µg/g) was highest in NEP, gallic acid (295.4±17.8 µg/g) and caffeic acid (24.1±1.3 µg/g) were highest in EP variety. Naringin (10136.0±17.4 µg/g), narirutin (14.0±0.4 µg/g), naringenin (20.7±1.7 µg/g) were highest in NEP variety. Significant reduction was observed for BP, lipid profile, IR, TNF-α, interleukin-6 and malondialdehyde in all grapefruit treated groups. Reduction in BP, total cholesterol, triglyceride, low-density lipoprotein, IR, TNF-α, interleukin-6 and malondialdehyde was high in 0.6gNEP (16.0, 36.0, 50.0, 66.0, 57.0, 47.0, 47.0 and 40.0%) and low in 0.8gEW (9.0, 7.0, 6.0, 13.0, 17.0, 17.0, 17.0 and7.0%), respectively. High-density lipoprotein was increased by 33.0% and 11.0% in 0.6gNEP and 0.8gEW, respectively. Significant difference was observed for BP, lipid profile, IR, TNF-α, interleukin-6 and malondialdehyde between high and low dosages administered. Edible and non-edible parts of white and pink grapefruit attenuated biomarkers of metabolic syndrome. However, non-edible pink variety was most efficacious.