Postharvest Quality and Safety in Fresh-Cut Vegetables and Fruits

NON-TECHNICAL SUMMARY: Crop production and postharvest management systems must be designed and implemented with sensory quality, nutritive quality, and safety to consumers as equal priorities. The microbial quality of pre and postharvest water plays a major role in the safety of fresh cut product. Several approaches will evaluate microbial food safety risks and will seek to provide a better understanding of novel options to prevent and control human pathogens on these non-cooked foods.

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APPROACH: The application of foliar treatments, virtually all contact-sprays on aboveground plant parts including fertility management, pest and disease control, plant growth regulators, or microenvironment modification, is an area of primary concern for the potential to contaminate fresh produce with infectious pathogens, whether as raw commodities or minimally-processed produce. Our approach concerns the evaluation of survival kinetics of pathogenic Salmonella serotypes, strains of Escherichia coli O157:H7, and Listeria monocytogenes inoculated as standard population density suspensions in common preharvest and postharvest fungicides or postharvest waxes in sterile water, at the unadjusted native pH of the final solution. Quantification of persistence and potential for multiplication is conducted on the appropriate selective and differential microbiological media. The comparative stress tolerance of Salmonella serotypes, applied as multi-strain mixtures, to pre and post application survival on produce surfaces and wound sites is being determined using DNA-based fingerprinting schemes, such as ERIC-PCR. During postharvest handling, clean, disinfected water is necessary to minimize the potential transmission of pathogens from water to produce, between produce within a lot, and between lots over time. Water-borne microorganisms, whether post-harvest plant pathogens or agents of human illness, can be rapidly acquired and taken up on plant surfaces. Hyperchlorination (use of high levels of chlorine) is commonly used by the fresh cut industry but has several known or potential negative product sensory, environmental and human health impacts. A variety of approaches are being taken to optimize water disinfection process controls with hypochlorite and other disinfectant treatments. Redox potential or Oxidation Reduction Potential (ORP) measured in millivolts is being evaluated as a standard for assessing, controlling, and documenting the suitability of postharvest water in various postharvest uses. By controlling and monitoring ORP, pH, conductivity, and turbidity a family of inactivation curves for non-spore forming bacteria, yeast, and fungal conidia or other spore-like structures are being developed in relation to water temperature and fresh-cut product (melons, leafy greens, brassicas, onions). Surface and sub-surface reduction of contamination of melons, primarily cantaloupe, by vapor heat is being evaluated for efficacy in microbial reduction and impact on visual and sensory quality of fresh-cut product. Heat treatments are being applied as steam, with and without elevated pressure. Sensitive methods for post-treatment recovery and enrichment of heat-stressed cells are being evaluated. Time:Temperature requirements for inactivation of bacteria are being determined against the impact of such regimes on quality. Sensory evaluations include objective (i.e. color, texture or firmness, soluble solids, total sugars, other components) and subjective (i.e. overall visual quality, decay, aroma and off-odor) measurements. Trained evaluators using hedonic scales do subjective measurements.
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PROGRESS: 1999/10 TO 2005/09<BR>
During this period the PI made over 60 presentations directly related to current research and technology in postharvest quality and safety of fresh fruits and vegetables at symposia, workshops, short courses, continuing education training sessions for extension advisors and USDA inspectors, course lectures, professional technical sessions, industry association meetings, environmental association or technical group meetings, and many other forums in California, across the U.S., and internationally. Compilations of presentations, proceedings, progress reports, CD-resources on food safety, and other materials were made accessible.
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IMPACT: 1999/10 TO 2005/09<BR>
The outcomes of the combined research and extension activities of this program have been heavily incorporated into elements of the Commodity Specific Food Safety Guidelines for the Production and Harvest of Lettuce and Leafy Greens and the Commodity Specific Food Safety Guidelines for the Production and Harvest of Fresh Market Tomatoes. These documents embody and are catalysts for the future direction of food safety management in these commodities and the produce industry as a whole. They were developed by a collaborative effort of industry, regulators, and academia which included the PI.