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United States Department of Agriculture

Agricultural Research Service

Title: X-Ray Microanalysis of Apples Treated with Kaolin Indicates Wax-Embedded Particulate in the Cuticle

Authors
item Curry, Eric
item Baer, D - DEPT. OF ENERGY, RICHLAND
item Young, J - DEPT. OF ENERGY, RICHLAND

Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 1, 2003
Publication Date: February 1, 2004
Citation: Curry, E.A., Baer, D., Young, J. 2004. X-ray microanalysis of apples treated with kaolin indicates wax-embedded particulate in the cuticle. Acta Horticulture Proceedings. 636:497-503.

Interpretive Summary: Sun-induced injury (solar injury) can be a costly problem in some years for tree fruit growers, especially in hot, arid regions. Recently, other researchers demonstrated that kaolin (clay) applied to the apples during periods of high solar radiation reduced solar injury. Because of the characteristics of the applied mineral, we wanted to know whether the particles would lodge in the micro-cracks of the cuticle and compromise the integrity of the peel. 'Gala' apples trees were treated with kaolin (Surround ) in mid-July, and fruit were sampled 1 and 7 days after treatment. Small sections of cuticle tissue were shaved from the fruit surface with a razor blade and flash frozen on an aluminum block held at -190ºC with liquid N2. Tissue was freeze-dried and examined using a field emission scanning electron microscope coupled with an energy dispersive x-ray microanalysis system capable of light element detection. Our analysis showed that because the structure of kaolin is much like that of the structure of the apple cuticle (plates) the kaolin microparticles may become embedded in the cuticle between individual wax platelets thereby incorporating the clay into the fruit cuticle. Quality of the fruit did not appear to be compromised.

Technical Abstract: 'Gala' apples trees were treated with kaolin (Surround) in mid-July, and fruit were sampled 1 and 7 days after treatment. Apples were gently rinsed with cold deionized water to remove loose surface material. Small sections of cuticle tissue were shaved from the fruit surface with a razor blade and flash frozen on an aluminum block held at -190ºC with liquid N2. The tissue was freeze-dried, coated with a thin film of carbon, and examined using a field emission scanning electron microscope coupled with an energy dispersive x-ray microanalysis system capable of light element detection. Qualitative secondary electron imaging combined with quantitative elemental compositional analyses indicated kaolin particles may become embedded in the cuticle between individual wax platelets.

Last Modified: 10/21/2014
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