|Mlikota Gabler, Franka|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2009
Publication Date: 9/1/2010
Publication URL: http://apsjournals.apsnet.org/
Citation: Romanazzi, G., Mlikota Gabler, F., Margosan, D.A., Mackey, B.E., Smilanick, J.L. 2010. Effect of Chitosan Dissolved in Different Acids on its Ability to Control Postharvest Gray Mold of Table Grape. Phytopathology. 99:1028-1036. Interpretive Summary: Table grapes rot after harvest unless actions are taken to retard this process. Sulfur dioxide gas is used to stop the rot, but it harms flavor and appearance of the grapes and leaves residues harmful to some people, so a chitosan treatment of grapes was evaluated for this purpose. Treatment of the grapes with chitosan, a natural product derived from crab shell, provided some control of Botrytis cinerea (the fungus that causes most of the rot), when dissolved in one of several acids, and was a promising replacement for sulfur dioxide, because it caused no harm to the grapes, left no residues, and was generally compatible with other commercial practices.
Technical Abstract: Chitosan is a natural biopolymer that must be dissolved in an acid solution to activate its antimicrobial and eliciting properties. Among 15 acids, chitosan dissolved in 1% solutions of acetic, L-ascorbic, formic, L-glutamic, hydrochloric, lactic, maleic, malic, phosphorous, and succinic. Chitosan solutions were adjusted to pH 5.6 before 10 seconds of immersion of harvested table grapes to control gray mold. The reduction in decay among single berries of several cultivars inoculated with 100,000 Botrytis cinerea conidia per ml before or after immersion in chitosan acetate or formate, followed by storage at 15C for 10 days, was about 70%. The acids alone at pH 5.6 did not control gray mold. Decay among clusters of two cultivars inoculated before treatment was reduced about 60% after immersion in chitosan lactate or acetate followed by storage for 60 days at 0.5C. The viscosity of solutions was 1.9 cp (ascorbate) to 306.4 cp (maleicate), and the thickness of chitosan coating on berries was 4.4 micrometers (acetate) to 15.4 micrometers (ascorbate); neither was correlated with solution effectiveness. Chitosan acetate was the superior treatment; it effectively reduced gray mold at cold and ambient storage temperatures, decreased CO2 and O2 exchange, and did not injure grapes.