Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 21, 2002
Publication Date: January 1, 2003
Citation: Bai, J., Hagenmaier, R.D., Baldwin, E.A. 2003. Coating selection for 'Delicious' and other apples. Postharvest Biology and Technology. 28:381-390. Interpretive Summary: It is well known that the quality of stored apples is affected by the type of wax coating applied in the packinghouse, but it is poorly understood how to predict such quality changes. For the present work we determined how quality was affected by the gas permeability of the coating. Accordingly, a series of coatings with measured permeabilities were applied to Delicious, Fuji, Braeburn and Granny Smith apples, and their quality monitored after 2 or 4 weeks at 20C for changes in quality. The shellac coating, which had lowest permeability, gave lowest internal O2, highest CO2 and prodigious accumulation of ethanol in Fuji. The Delicious apples with shellac, on the other hand, did not have excessive ethanol and retained firmness somewhat better. Candelilla and carnauba-shellac coatings, which had moderate values of permeability, maintained more optimal internal O2 and CO2 and better quality for Fuji, Braeburn, and Granny Smith. In general the gas permeabilities of the coatings were useful as a predictor of quality changes.
Technical Abstract: The gas permeabilities of shellac and several experimental coating formulations, including candelilla wax and shellac-carnauba were measured. These coatings, selected to have a very wide range of gas permeabilities, were applied to freshly harvested or 5-month long-term commercially stored Delicious, Fuji, Braeburn and Granny Smith apples, respectively. The coated apples were monitored during storage of 2 or 4 weeks at 20C for changes of internal gas level, respiration rate and other 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 very low internal O2 (< 2 kPa) with both freshly harvested and 5-month-stored apples, and the freshly-harvested Braeburn had very high internal CO2 (25 kPa). The 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, although even these coatings may present too much of a gas barrier for Granny Smith. 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.