Calcium uptake through skins of sweet cherry fruit: Effects of different calcium salts and surfactants

Abstract Increasing fruit calcium (Ca) raises the quality of sweet cherry fruit. The objective was to quantify Ca mass per fruit following exposure of developing fruits to Ca salt solutions by submersion or by spraying. Mass of Ca per fruit was quantified by atomic absorption spectrometry. Time courses of Ca mass per fruit following treatment with Ca-chloride or Ca-formate revealed increasing Ca mass with time. Calcium uptake by late stage III fruit (harvest mature) generally exceeded that by stage II fruit (pit mature). Increasing Ca salt concentration increased Ca mass per fruit. The increase in Ca mass was reduced, if the pedicel cavity had previously been sealed with silicone rubber, but sealing the stylar scar had little effect. Submersion and spraying with a range of Ca salts increased Ca mass per fruit, but Ca uptake was greatest for Ca-nitrate and least for Ca-lactate or Ca-heptagluconate. There was little difference in uptake between Ca-acetate, Ca-chloride, Ca-formate or Ca-propionate. The effects on Ca uptake of additions of surfactants depended on the surfactant, the mode of application, the fruit cultivar and the developmental stage. Spraying with Ca salts in combination with Glucopon CSUP and Break-Thru S 240 showed no gain in Ca. Occasionally with ‘Hedelfinger’, Ca uptake was actually decreased by the addition of surfactant, compared with the no-surfactant controls. The latter likely resulted from a decrease in the volume of Ca solution retained on the sprayed fruit surface due to more complete surface drainage with Break-Thru S 240. The results show that spraying fruit with solutions of various Ca salts increases Ca mass per fruit. The increase is the result of penetration of Ca through the fruit skin and also through the pedicel:fruit junction. The various anion partners of the Ca salts examined made surprisingly little difference to the amount of Ca penetrating the fruit skin. Calcium uptake from those salts having lower points of deliquescence and higher water solubility was slightly greater.