Mango fruit calcium levels and the effect of postharvest calcium infiltration at different maturities

Abstract

Calcium concentrations in ‘Kensington’ and ‘Sensation’ mango fruits were measured throughout fruit development on the tree. Flesh calcium concentrations fell from 2.1 to 0.8 mg/g d.w. for ‘Kensington’ and 1.6 to 0.8 mg/g d.w. for ‘Sensation’ as the fruits grew into maturity. Cuticle thickness in both cultivars varied only slightly during growth. Increases in cell wall thickness and in cell length and breadth were similar for both cultivars. Cell wall thickness was greatest in the outer flesh, while cell size increased most in the inner flesh of the fruit. Calcium concentration profiles were determined in ‘Kensington’ fruit harvested at normal commercial maturity for untreated fruit and fruit vacuum infiltrated (−33 kPa) with 4% (w/v) calcium chloride. Similar profiles were obtained for both cases. The skin, outer flesh, middle flesh and inner flesh had sequentially decreasing calcium concentrations. Concentrations ranged between 0.371 mg/g d.w. (skin) and 0.095 mg/g d.w. (inner flesh) for untreated ripened fruit. Corresponding concentrations for calcium-treated ripened fruits were 0.547–0.086 mg/g d.w. Calcium-treated fruits exhibited no differences in colour or firmness changes and weight loss during shelf life as compared to control fruit. Some lenticel damage was observed as a result of calcium infiltration. Shelf life studies were undertaken on control and vacuum infiltrated ‘Kensington’ and ‘Sensation’ mango fruits harvested at early (−3 weeks), middle, and late (+3 weeks) stages of maturity and on ‘Irwin’ and ‘Palmer’ mangoes harvested at middle maturity, i.e. normal commercial harvest time. Calcium levels in skin tissue of only ‘Kensington’ and ‘Palmer’ mangoes were slightly higher for calcium-treated than for untreated fruits. Calcium levels in flesh tissue were not increased by vacuum infiltration of calcium into any of the cultivars or maturities. Treatment with 4% (w/v) calcium chloride did not extend the shelf life of fruits of any of the four cultivars.