Alternatives to shellac coatings provide comparable gloss, internal gas modification, and quality for 'delicious' apple fruit

Abstract

Zein, starch, polyvinyl acetate (PVA), carnauba, and carnauba-polysaccharide (CPS) coatings were compared with a commercial shellac coating using controlled atmosphere stored 'Delicious' apples (Malus xdomestica Borkh). Coated apples were stored in air at 2°C for 2 weeks and then removed to 21°C for an additional two weeks to simulate marketing conditions. Gloss, internal O2 and CO2 partial pressures, weight loss, flesh firmness, and contents of sugars, acids and volatiles were measured on 0, 2, and 4 weeks after coating treatment. Starch- and carnauba-coated apples had high initial gloss, similar to that found for shellac-coated fruit. Gloss of all coated fruit decreased similarly during the 4-week evaluation period, although all of the coated fruit were glossier than uncoated controls. For uncoated apples, the differences of O2 and CO2 partial pressure between internal and ambient atmosphere were ≅1 kPa at 2°C, and these increased by a further 2 kPa after transfer to 21°C. Fruit coated with shellac and starch had >10 kPa CO2, and <10 kPa O2 at 21°C. Zein-, PVA- and carnauba-coated apples showed a less modified internal atmosphere (6-7 kPa CO2,11-15 kPa O2). Internal partial pressures of O2 and CO2 were inversely related for most coatings, except for the CPS coating, for which partial pressures of both CO2 and O2 were low. Carnauba-, PVA-, and shellac-coated fruit lost less weight than uncoated fruit. Starch-, shellac., and CPS-coated fruit were firmer than those from other coating treatments, and all coated fruit were firmer than uncoated control. Titratable acidity was higher in the fruit coated with CPS, starch, and shellac than in uncoated control. Ethyl alcohol and ethyl esters accumulated in starch-, shellac-, and CPS-coated fruit kept at 2°C, but, levels of these volatiles decreased after transfer of fruit to 21°C. Carnauba, PVA and zein coatings compared favorably to shellac for gloss and other quality characteristics.