Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/5/2002
Publication Date: 5/1/2003
Citation: Bai, J., Alleyne, V., Hagenmaier, R.D., Mattheis, J.P., Baldwin, E.A. 2003. Formulation of zein coatings for apples (Malus domestica Borkh). Postharvest Biology and Technology. 28:259-268. Interpretive Summary: Red apples are often coated with edible shellac, which is also used to coat M&M candy and candy canes, to increase shine and reduce shriveling. However, this coating can cause a chalky appearance on the apples, can restrict the ability of the fruit to "breathe", and is associated with non-food uses. A new coating was developed from corn protein that is also shiny, but with a more wholesome appeal compared to shellac, from a consumer's point of view. This formulation was tested on Gala apples and performed as well as a commercial shellac formulation.
Technical Abstract: High gloss coatings are used to improve apple fruit (Malus domestica, Borkh) appearance and subsequent sales. The industry standard has been shellac which has problems with whitening, low gas permeability, and association with non-food uses. Zein, a natural corn protein, was used to formulate alternative, shiny coatings by dissolving zein in aqueous alcohol lwith propylene glycol (PG). Coating gloss was dependent on PG and zein contents. At least 4% (by weight) PG was necessary for adequate gloss. However, increasing levels of both compounds resulted in increased gloss. Discoloration or whitening of the fruit surface was reduced by decreasing zein content to less than 11%. Permeability to CO2, O2 and water vapor was strongly dependent on the zein content in the coating. Internal gases of coated 'Gala' apple were modified to 3 to 12 kPa CO2 and 19 to 5 kPa O2, respectively, by increasing zein content in the coating. An optimum formulation with 10% zein and 10% PG was developed, applied to 'Gala' apple, and was found to extend shelf life as well as maintain overall fruit quality comparable to a commercial shellac coating.