Effect of Calcium and Other Minerals on Ripening of Tomatoes

Ripening of green tomatoes (Lycopersicon esculentum) cv. Daydream, as expressed by change of colour, increased ethylene evolution and respiration, was inhibited when the calcium content of the fruit was raised to greater than 40 mg/100 g fresh weight (1 mmol Ca/100 g). The inhibition of ripening was long-lasting as such fruit showed no signs of ripening even after 6 weeks storage at 20°C, and the application of 1000 �l/l ethylene for 3 weeks had no effect. Application of calcium also inhibited the ripening process in tomatoes that had commenced ripening. Further change in colour was halted and a reduction in respiration and ethylene evolution was observed when calcium was applied at any stage of ripening including fully ripe. Inhibition of ripening was not specific to calcium as other divalent metal ions-manganese, cobalt and magnesium-were as effective as calcium, while the monovalent metal ions sodium and potassium were less effective than calcium but did give some retardation of ripening. Silver was as effective as the divalent metals in inhibiting colour change but its effect on ethylene production was similar to that obtained with sodium and potassium.