Antimicrobial and antioxidant activities of Citrus sinensis var. late Valencia fruits at various stages of development

Fruit juice extracts of Citrus sinensis var. late Valencia at different stages of development (3, 6, 10 and 12 months and fallen senescent fruits) were investigated for antimicrobial and antioxidant activities. Antimicrobial activity was determined using a modified Kirby-Bauer agar diffusion method and minimum inhibitory concentrations (MIC) were determined by the micro broth dilution method against strains of Bacillus subtilis NCTC 10073, Candida albicans ATCC 10231, Escherichia coli ATCC 25922, Proteus vulgaris NCTC 4175, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 25923. Antioxidant activity was evaluated by the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical scavenging method using N-propyl gallate as standard antioxidant. IC50 values were then determined. Results revealed that the fruit juice extracts demonstrated broad spectrum antibacterial as well as antifungal activity with MIC values ranging from 8.00 to 20.00%, 16.00 to 28.00% , 24.00 to 32.00%, 28.00 to 40.00% and 32.00 to 44.00% v/v for 3, 6, 10, 12 months fruits as well as fallen fruits senescence, respectively. The antimicrobial activity was observed to decrease with increasing age of the fruits. The fruit juice extracts also demonstrated antioxidant activity with IC50 values of 0.4424, 0.6841, 7.357, 12.65 and 41.65% v/v for 3, 6, 10, 12 months and fallen fruits senescence, respectively. The antioxidant activity was also observed to decrease with increasing fruit age.