Effect of partial pressure infiltration of calcium into ‘Kensington’ mango fruit

Abstract

Summary.‘Kensington’ mango fruit harvested at the mature green stage were partial pressure (vacuum) infiltrated with calcium (4 g Ca ²⁺/L as CaCl₂) at 3 reduced pressure levels (–33, –66 and –99 kPa). Concentrations of Ca²⁺ in unripened calcium-treated fruit were about 1-, 2- and 3-fold higher, respectively, than Ca²⁺ concentrations in the skin and flesh of control (untreated; i.e. not vacuum infiltrated) fruit. For example, skin tissue Ca²⁺ concentrations of control fruit and of those treated at –33, –66 and –99 kPa were 1.51, 1.93, 3.42 and 5.01 mg Ca²⁺/g dry weight, respectively. Concentrations of Ca²⁺ in the skin of both control fruit and of Ca²⁺ -treated fruit were consistently higher, by about 2-fold, than those in the fruit flesh. Compared with the –33 kPa infiltration treatment, Ca²⁺ levels in the fruit flesh were increased by only about 2-fold by further reductions in the partial pressure infiltration levels to –66 or –99 kPa. Infiltration of Ca²⁺ into mango fruit was apparently via lenticels and along xylem conduits open at the cut pedicel. These infiltration pathways were revealed by inclusion of Brilliant Blue dye in the Ca²⁺ solution. Undyed and dyed lenticels were separately excised for Ca²⁺ analysis. Dark (dyed) lenticels had higher Ca²⁺ concentrations (1.86 ± 0.11 mg Ca²⁺/g dry weight) than light (undyed) lenticels (0.83 ± 0.19 mg Ca²⁺/g dry weight). Partial pressure infiltration of Ca²⁺ at any of the 3 subatmospheric pressure levels did not result in shelf life extension. Fruit infiltrated at –66 and –99 kPa exhibited injuries, which included exacerbated lenticel blackening and anaerobic off-odour and taste evident at the end of shelf life. In comparison, both control (untreated) mango fruit and those infiltrated with Ca²⁺ at –33 kPa ripened normally.