Biochemical Characteristics and Antioxidant Properties of Citrus Juice from Lemon (Citrus limon), Lime (Citrus aurantifolia) and Grapefruit (Citrus paradisi) as Influenced by Degree of Ripening

The influence of degree of ripening (unripe, half-ripe and ripe) of citrus fruits (lemon, lime and grapefruit) on the biochemical characteristics and antioxidant potential of their juices was investigated. The juice yield from the citrus fruits was affected by the level of ripening as the highest juice yield was obtained when the fruits were at ripe stage giving 25.2 mL/100 g (lemon), 43.3 mL/100 g (lime), and 21.1 mL/100 g (grapefruit). The biochemical characteristics of the citrus juices revealed that the pH values were generally increasing with an increasing level of ripening particularly for lime and grapefruit while the pH of lemon juice was decreasing with an increase in the degree of ripening. The lowest pH values exhibited by the citrus fruits were 2.87 (ripe lemon), 2.16 (unripe lime), and 3.27 (unripe grapefruits). The total acidity of the citrus juices essentially exhibited an inverse relationship with their corresponding pH values. The highest ascorbic acid contents of the juices were 51.3 g/100mL (unripe lemon), 38.9 g/100mL (unripe lime), and 44.7 g/100mL (unripe grapefruit) while the highest total phenolic contents were 722 µg GAE/mL (unripe lemon), 207 µg GAE/mL (unripe lime), and 646 µg GAE/mL (unripe grapefruit); indicating a significant impact of degree of ripening on the parameters. The antioxidant activity of the citrus juices using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical assay revealed a significant influence of degree of ripening and juice volume on the activity. The percent inhibition of DPPH free radical by the juices was generally higher at an unripe stage of fruit maturity as well at greater juice volume. The ferric-reducing antioxidant potential (FRAP) of the citrus juices was also influenced by the level of ripening of the fruit. The FRAP values were generally higher at unripe stage which were 3.72 µ mol Fe(II)/g (unripe lemon), 4.98 µ mol Fe(II)/g (unripe lime) and 9.53 µmolFe(II)/g (unripe grapefruit).