Coating selection for ‘Delicious’ and other apples

The gas permeabilities of shellac and several experimental coating formulations, including candelilla wax and shellac-carnauba were measured. These coatings, selected to have a wide range of gas permeabilities, were applied to freshly harvested and 5-month commercially stored ‘Delicious’, ‘Fuji’, ‘Braeburn’ and ‘Granny Smith’ apples. The coated apples were monitored during storage of 2 or 4 weeks at 20 °C for changes in internal gases level, and for quality parameters (surface gloss, weight loss, flesh firmness, Brix, titratable acidity and ethanol content). The shellac coating resulted in maximum fruit gloss, lowest internal O2, highest CO2, and least loss of flesh firmness for all of the varieties. The ‘Granny Smith’ with shellac had low internal O2 (<2 kPa) with both freshly harvested and 5 month-stored apples, and the freshly-harvested ‘Braeburn’ had high internal CO2 (25 kPa). This excessive modification of internal gas induced an abrupt rise of the respiratory quotient, prodigious accumulation of ethanol in both ‘Braeburn’ and ‘Granny Smith’, and flesh browning at the blossom end of ‘Braeburn’. In addition the shellac coating gave an unusual accumulation of ethanol in freshly harvested and 5 month-stored ‘Fuji’. Candelilla and carnauba-shellac coatings maintained more optimal internal O2 and CO2 and better quality for ‘Fuji’, ‘Braeburn’ and ‘Granny Smith’ apples, although even these coatings may present too much of a gas barrier for ‘Granny Smith’. Therefore, this research recommends the best coatings as shellac for ‘Delicious’, and carnauba-shellac for ‘Braeburn’ or ‘Fuji’. Best for ‘Granny Smith’ would seem to be a high-permeability wax similar to polyethylene, which has not been approved for apple by FDA. In general, the gas permeabilities of the coatings were useful as an indicator of differences in coating barrier properties, but did not account for differences in pore blockage.