Formulation of Zein coatings for apple (Malus domestica Borkh)
J. Bai ,V. Alleyne ,R.D. Hagenmaier , J.P. Mattheis, and E.A. Baldwin
Postharvest Biology and Technology, Volume 28, Number 2, May 2003 , pp. 259-268
2003
บทคัดย่อ
High-gloss coatings are often used to umprove the appearance and sales of apple fruit (Malus x somestica, Borkh). The industry standard coating has been shellac, which has problems with low gas permeability, and association with nonfood uses. There is also a problem with whitening that occurs after transfer of shellac-coated fruit from low storage temperatures to ambient marketing conditions, resulting in condensation of water vapor on the cold fruit surface. Zein, a natural corn protein, was used to formulate alternative, shiny coatings consisting of zein, propylene glycol (PG), alcohol and water. Coatings were evaluated on eGalai apples stored at 20 0C. At least 4% (by weight) PG, was necessary for adequate gloss, but higher levels of both zein and PG resulted in increased gloss. The gloss also varied due to zein content, with 10% giving about the same gloss as shellac-coated fruit. Whitening was low with zein content less than 11 %. Permeability of CO2 , O2 and water vapor was strongly dependent on the zein content in the coating. Internal gases of coated apples were modified to 3 to 12 kPa CO2 and 19 to 5 kPa O2 , respectively, by increasing zein content in the coatings. An optimum formulation with 10% zein and 10% PG was developed and found to extend shelf life and to maintain overall quality comparable to a commercial shellac coating.