Nutritional Properties, Antioxidant and Antimicrobial Activity of Seed and Peel Extracts of Grapefruit (Citrus paradisi) on Some Selected Clinical Organisms

Abstract

The need for new antimicrobial agent is linked with the emergence of strains that are restraint to most antibiotics and plants are safer alternative source of antimicrobials. This study aimed at determining the nutritional properties, phytochemical constituents, antioxidant and antimicrobial  activity of seed and peel Citrus paradisi. The test organisms were obtained from a tertiary hospital were analyzed using conventional microbiological methods. The ethanol and aqueous extracts of C. paradisi was obtained using the rotary evaporator. Antimicrobial activity was determined using agar well diffusion method. Proximate composition of seed and peel of C. paradisi were moisture, protein, ash, fibre, lipid and carbohydrates. Qualitative phytochemical constituents revealed the presence of alkaloids, saponin, tannin and flavonoids, and Quantitative phytochemical constituents revealed 19.41 mgGallic acid equivalent/g and 8.07 mgGallic acid equivalent/g of total phenols of ethanolic and aqueous peel extracts respectively. The ethanolic extract of seed had phenolic content of 3.73 mgGAE/g. The ethanolic peel and aqueous seed extracts showed higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity of 35.32%  and 25.32% respectively. The ethanolic seed extract of C. paradisi exhibited antimicrobial activity against all the bacterial test isolates at different concentrations. At 500mg/ml and 250mg/ml, P. aeruginosa showed the mean zone of inhibition of 18mm respectively. The largest mean zones of inhibition for S. aureus and E.coli were seen at 500mg/ml and 250mg/ml with 20mm and 27mm respectively. The ethanolic peel extract of C. paradisi exhibited antimicrobial activity at 500mg/ml against P. aeruginosa and  S. aureus, with the largest zones of inhibition of 25mm and 20mm respectively. At 250mg/ml, E. coli, had the largest mean zone of inhibition of 25mm. No antimicrobial activity was observed for both ethanolic peel and seed extracts of C. paradisi against Aspergillus spp. The aqueous extract of the seed of Citrus paradisi at the different concentrations showed no antimicrobial activity against both the bacterial and fungal isolates. The aqueous extract of the peel had antimicrobial effect on P. aeruginosa at 125mg/ml with mean zone of inhibition of 15mm. At 500mg/ml S. aureus and E. coli exhibited zones of inhibtion of 15mm and 20mm respectively. No zone of inhibition was observed with Aspergillus spp. This investigation indicates the peel of C. paradisi has medicinal activity and holds the potential as therapeutic agent for treating microbial infections.