559 HORTSCIENCE, VOL. 37(3), JUNE 2002 HORTSCIENCE 37(3):559–563. 2002. Alternatives to Shellac Coatings Provide Comparable Gloss, Internal Gas Modification, and Quality for ‘Delicious’ Apple Fruit Jinhe Bai, Elizabeth A. Baldwin 1 , and Robert H. Hagenmaier U.S. Department of Agriculture, Agricultural Research Service, Citrus & Subtropical Products Research Laboratory, 600 Avenue S, NW, Winter Haven, FL 33881 Additional index words. Malus ×domestica, shiny, firmness, modified atmosphere, volatile 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 ×domestica 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 O 2 and CO 2 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 O 2 and CO 2 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 CO 2 , and <10 kPa O 2 at 21 °C. Zein-, PVA- and carnauba-coated apples showed a less modified internal atmosphere (6–7 kPa CO 2 , 11–15 kPa O 2 ). Internal partial pressures of O 2 and CO 2 were inversely related for most coatings, except for the CPS coating, for which partial pressures of both CO 2 and O 2 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. tive to package atmosphere (Bai et al., 1990), these results suggested that the off-flavor de- veloped because either internal CO 2 exceeded 7–9 kPa, O 2 declined to 5–7 kPa, or both. In this research, we developed several ed- ible and shiny coatings from alternative mate- rials, observed how they affected internal gases, flavor compounds, and subsequently the qual- ity of the coated apples, in an effort to find alternative coatings to shellac. The alternative materials included zein and starch, which are food ingredients with a wholesome image; polyvinyl acetate, which gives high gloss and is an approved food additive (Hagenmaier and Grohmann, 1999); carnauba wax, a natural plant wax; and a natural complex polysaccha- ride. Zein coatings have been used on candy, dried fruit, nuts, and meats (Baker et al. 1994). Zein also was evaluated on tomatoes resulting in a modified internal atmosphere, color change, inhibition of weight loss, and delayed softening (Park, 1991). Carnauba wax has been used commercially to coat apple, and does not discolor, but has less gloss than shellac. Preliminary experiments showed that application of carnauba coatings resulted in less modification of the internal atmosphere in coated fruit than did shellac, and was more effective in preventing weight loss. Polyvinyl acetate-coated apples had higher internal O 2 partial pressures and less alcohol accumula- tion in fruit compared with shellac (Hagenmaier and Grohmann, 1999). Material and Methods ‘Delicious’ apples (Malus ×domestica Borkh.) were stored in commercial CA (1 kPa for both O 2 and CO 2 at 0.5 °C and 90% to 95% RH) in Washington State for 4–5 months, then transported to Florida in a refrigerated truck in Mar. 2000. Uniform (180–210 g) defect-free fruit were equilibrated at room temperature (25 °C) for 24 h, prior to application of coat- ings. Coatings were applied manually, using 0.5 mL/fruit, spread evenly over the fruit sur- face (surface area of ≈200 cm 2 ) using latex gloved hands. This resulted in a coating thick- ness of ≈25 μm when wet, which becomes thinner as the coating dries. Each fruit was inspected for complete coverage. Instead of coating, water was used for control fruit. A pilot-plant scale conveyor dryer (Central Florida Sales and Service, Auburndale, Fla.) was used to dry fruit (including controls) at 50 °C for 5 min. All fruit (except those processed for initial, day 0 samples) were stored at 2 °C for 2 weeks, then transferred to 21 °C for a further 2 weeks, to simulate marketing conditions. The treatments included experimental zein-, starch-, polyvinyl acetate (PVA)-, and carnauba-polysaccharide (CPS)-based formu- lations, as well as commercial carnauba- (Natu- ral Shine TM 8000; EcoScience, Orlando, Fla.), and shellac-based (Apple Wax 55; EcoScience) coatings and uncoated controls. The main components of the experimental formulations (expressed as percentage by weight) were: 1) zein (8% defatted zein, 8% propylene glycol, 25% isopropanol, 25% etha- Most ‘Delicious’ apples marketed in the United States are coated with shellac or a mixture of shellac and carnauba wax. Shellac has a problem with discoloration (whitening) (Baldwin, 1994; Hagenmaier and Shaw, 1992) which limits marketability, and is sometimes associated with nonfood uses. The latter point might some day be viewed negatively by con- sumers; therefore, it would seem prudent to develop alternative coatings. Furthermore, shellac is currently not listed as “generally recognized as safe” (GRAS) by the U.S. Food and Drug Administration (FDA). High gloss is considered by the industry to be beneficial for red apple sales. Recently, it has become common to see high gloss coat- ings on green apples as well. Reducing water loss and respiration rate also helps extend shelf-life of apples previously held in con- trolled atmosphere (CA) or air. Coatings af- fect the internal atmosphere of fruit and, there- fore, also can potentially reduce the respira- tion rate. Internal O 2 and CO 2 partial pressures of uncoated ‘Delicious’ apples at ambient temperature were 17–20 kPa and 2–4 kPa respectively (Alleyne and Hagenmaier, 2000; Bai et al., 1990). Coatings cause an increase in internal CO 2 and a decrease in O 2 partial pres- sures because of fruit respiration, in a manner similar to modified atmosphere (MA) packag- ing. Shellac coating on ‘Delicious’ apples raised internal CO 2 to ≈10 kPa, and reduced O 2 to ≈9 kPa at ambient temperature, and led to ethanol accumulation of ≈10 times that of uncoated control (Alleyne and Hagenmaier, 2000). The gas changes caused by shellac coatings were moderated by adding carnauba or candelilla wax to the formulations. Off- flavor was induced in ‘Starking Delicious’ apples stored in MA packaging at 8 °C, with 6 kPa CO 2 and 7–9 kPa O 2 partial pressure in the package (Ueda et al., 1993). Assuming an additional gradient of 1–3 kPa O 2 and CO 2 partial pressures for internal atmospheres rela- Received for publication 3 Apr. 2001. Accepted for publication 5 Sept. 2001. Mention of a trademark or proprietary product is for identification only and does not imply a guarantee or warranty from the U.S. Dept. of Agriculture. The U.S. Dept. of Agri- culture prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. 1 To whom reprint requests should be addressed. E-mail address: ebaldwin@citrus.usda.gov