Jan. 1, 2013 - Dec. 31, 2014Award Number
Qixin Zhong, Ph.D.
University of Tennessee
P.M. Davidson, F. CritzerResources
The netted surfaces of cantaloupes provide harborage sites for pathogens that are protected from washing and sanitizing and can continue to proliferate during storage. Antimicrobial coatings can potentially improve microbial safety and quality of cantaloupes but have not been studied extensively. Application of antimicrobials is somewhat complicated because they can be absorbed by components of cantaloupes which could reduce their activity. Thus sustained release of antimicrobial compounds from coatings is needed to maintain sufficient quantities to inhibit microorganisms on cantaloupe rinds. In this project, we propose to study novel antimicrobial coating systems to solve several challenges of improving safety and quality of cantaloupes. We propose to use plant-based food antimicrobials, essential oils, to develop systems that can overcome barriers to diffuse into cavities on cantaloupe surfaces and continuously release antimicrobials therein. The technology also can maintain visual appearance of cantaloupes and reduce moisture loss during storage. Specific research objectives are proposed to develop such technology and characterize physical and antimicrobial properties of coatings, as well as impacts on quality of cantaloupes. Coatings have already been adopted in the produce industry, and the novel technology can be applied to other melons and fresh produce products for enhanced microbial safety and quality.
Cantaloupes have been linked to several outbreaks of foodborne illness due to contamination by pathogens such as Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella. It is becoming clear that netted rinds of cantaloupes are topographically irregular and pathogens tend to adsorb and be trapped in cavities. Conversely, the microscopic cavities induce capillary forces that keep sanitizers such as hypochlorite outside the concave areas, which has been correlated to poor sanitization performance. Therefore, strategies are needed to overcome capillary forces, e.g., by adopting an appropriate surfactant to lower interfacial tension and thus capillary forces so that sanitizers and other antimicrobials can gain access to the protected areas where pathogens are harbored. Further, because cantaloupes could be stored for two weeks or longer, intervention systems such as antimicrobial coatings are needed to insure microbial safety during storage. In addition to inhibiting pathogenic and spoilage microorganisms, antimicrobial coatings that are transparent are desirable to maintain visual appearance and be effective in preventing quality losses like dehydration and oxidation.
In this project, we propose to study novel antimicrobial coating systems that can overcome the problems associated with safety and quality of cantaloupes. Based on our recent research findings, we propose to prepare transparent nanoemulsions of essential oils (EO) from clove, cinnamon, and thyme that will be incorporated in film-forming hydrocolloids to coat cantaloupes. We hypothesize a phase-inversion temperature method can be effective in preparing transparent nanoemulsions of EO that can be further used to prepare transparent coatings. We further hypothesize that the proposed novel antimicrobial coatings are effective systems in improving safety and quality of cantaloupes. Because surfactants such as Tween 80 are used in preparing nanoemulsions, these nanoemulsions are expected to overcome capillary forces and diffuse to cavities on cantaloupe surfaces to inhibit potential pathogens therein. Further, vapor pressure and sustained release of volatile EO will be controlled by inclusion of soybean oil in the oil body of emulsions. The oil-containing coatings also are expected to improve barrier properties for loss of water vapor and thus quality of cantaloupes during storage.
The hypotheses will be tested in the following research objectives: (1) identify conditions of preparing nanoemulsions of EO, (2) characterize physical properties of films and release properties of EO, (3) evaluate antimicrobial effectiveness of coatings against spoilage and pathogenic microorganisms on cantaloupes, and (4) assess the cost of antimicrobial coatings and impacts on the quality of cantaloupes. The objectives will be led by a team with overall expertise in food biophysics, food microbiology, food antimicrobials, and produce safety and quality.
The project directly addresses the priority area of 2.2 in the RFA. Although only cantaloupes are studied this project due to time limitation, we expect the novel antimicrobial coatings can be applied to numerous fresh produce products for improved safety and quality. Because coatings have already been used for produce products such as citrus and apples, we anticipate the successful coating formulations can be timely translated to the produce industry.