Biochemistry of ripening of kagzi lime (Citrus aurantifolia Swingle) fruit

Kagzi lime fruits harvested at 6 ripening stages, i.e. dark green, light green, peel colour turning, half yellow, three-fourths yellow and full yellow (ripe) were analysed. Fruits took 165 ± 10 days to reach peel colour full yellow (ripe) stage from fruit set. Fruits showed a gradual decline in respiration and produced no detectable level of ethylene during ripening. Total sugars, titrable acidity, sugar to acid ratio, sucrose, glucose, fructose, ascorbic acid, peel and pulp oil, Ca, Fe, Cu contents in pulp and carotenoids in skin increased. The Zn, Mn, Na, K and Mg showed marginal changes; dry matter and N in pulp and chlorophyll decreased in peel during ripening. Six non-volatile organic acids, namely pyruvic, succinic, fumaric, oxalo-acetic, malic and citric acids were identified and quantified by GC studies. Citric acid formed the major acid at different ripening stages. The fruit softening enzymes, PE, PG and cellulase activity in general increased, while β-galactosidase decreased during ripening. Peroxidase, phosphorylase activity decreased and PPO, amylase activity increased upto colour break stage and then declined at the later ripening stages. The sucrose metabolising enzymes, SPS, SS and AIV activity pattern showed a non-existence of relationship with sucrose content. Glycolytic enzymes, hexokinase, PFK and PK activity registered only marginal changes during ripening. Gluconeogenic enzyme G6Pase activity declined and FBPase increased during ripening. PEPCK increased; malic enzyme PEPC decreased and pyruvate decarboxylase showed marginal changes during ripening. Ethylene forming enzyme activity was not detected at different ripening stages.