Quality and Safety of Fresh-Cut Vegetables and Fruits

Non-Technical Summary:<br/>
Consumption of fresh-cut produce increased at an annual rate of approximately 10% from 1995 to 2004 and the market is estimated at $10-12 billion annually. Postharvest losses of fresh-cut produce are difficult to estimate but given their highly perishable nature, the retail value of fresh-cut produce losses may exceed $1 billion annually. The appearance, convenience, and generally high nutritive value of fresh-cut vegetables and fruits drive sales of fresh produce, but repeat sales of the fresh-cuts is dependent upon assurance of its safety and the products having pleasing texture and flavor. The industry primarily relies on established technologies derived mainly from practical experience to maintain visual quality and shelf-life with less consideration of the quality characteristics that drive repeat sales such as good flavor retention, maintenance of an appealing texture (crispness, crunchiness), and increased microbial quality leading to extended shelf stability and food safety. Through interaction with the industry we know that current technologies, especially for fresh-cut fruits, do not provide the shelf stability needed to supply long distance domestic markets with optimum flavor quality. As a result of physiological and microbial deterioration occurring during storage and marketing of fresh-cut produce, there is a need to develop effective, non-damaging treatments for maintaining their quality and safety. Integration of physiological, pathological, food safety and instrumental and sensory quality measurement concepts is essential for developing the most effective handling procedures and innovative, new technologies for maintaining quality and shelf stability of fresh-cut products. Much experimental work is needed to optimize and integrate new and emerging treatments in diverse fresh-cut products. This fact supports the proposed integrated approach of having parallel projects in different states and of focusing the research into specific areas of importance. Relevant information will be available to fresh-cut processors to assist them in making decisions to best maintain fresh-cut product quality and safety. The fresh-cut industry will achieve considerable savings from reductions of product losses and recalls. Consumers will benefit from increased availability of fresh-cut products with improved sensory quality and higher nutritional value. Incidence of fresh-cut products at retail with insufficient shelf life for consumer satisfaction will decrease. Human health will be improved as a result of increased consumption of vegetables and fruits. Availability of best-practice guidance and standardized risk assessment methods for treatments will reduce the likelihood of food safety outbreaks involving fresh-cut products. Food safety risk will be reduced through availability of new, more efficacious, strategies for controlling human pathogens. Researchers will have standard protocols for quantifying flavor-based shelf life and standard microbiological methods. Longer-term scientific benefits will be derived from obtaining a better understanding of ethylene and stress physiology of wounded plant tissues.
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Approach:<br/>
Obj. 1: Shelf life in terms of appearance, texture, nutritional value, and flavor and interactions between flavor components will be determined. Chemical and sensory data will be combined to determine aroma profile and sugar/acid ratios or off-flavor. Standardized sensory evaluation methods and objective color, texture, and composition methods will be used.
<br/>Obj. 2: Genotype selections will be based on ripening characteristics, appearance and flavor, texture and nutritional value. Sensory evaluations will be conducted by untrained panelists and trained judges. Intensity and overall acceptability characteristics will be evaluated and standardized. We will evaluate 1-MCP and heat treatments and coordinate with microbiologists in testing sanitizers. Pectinesterase application with and without calcium in order to firm the tissue by creating pectin crosslinking will be evaluated. Rinsing the cut fruit with buffered alkaline solution will also be tested to determine the role of vacuole rupture in watersoaking and softening due to activation of hydrolases.
<br/>Obj. 3: We will investigate how postharvest treatments such as MAP and heat can be used to enhance the plant antioxidant system. Ethylene-dependent and ethylene-independent wound responses will be investigated using 1-MCP. The role of membrane deterioration in terms of electrolyte efflux and analysis of lipoxygenase and phospholipase action will also be investigated. Standard spectrophotometric and HPLC analyses of antioxidant compounds and capacity will be used. Antioxidant system enzyme activities will be measured as previously described (Soto-Zamora et al., 2005). Lipid class analysis will be as previously described by Picchioni et al. (1996), and lipid degrading enzyme activity as described by Todd et al. (1992).
<br/>Obj. 4: 1) We will develop research best-practice guidance and standardized methods for food safety risk assessments of fresh-cut product quality enhancing treatments or efficacy of disinfection measures. 2) We will evaluate the influence of inoculum production, method of application, rate of drying, potential for sub-lethal injury on quantitative and qualitative recovery of pathogens, duration and condition of storage, biofilm development, and method of viable recovery.
<br/>Obj. 5: Commodity tolerance to hot water and effects on pathogen populations will be determined. Tomato, pineapple and mango will be inoculated with pathogens or surrogates. Potential for injured cells to grow will be evaluated by plating to selective and nonselective media. The impact of hot water immersion on produce quality will be evaluated using sensory evaluation and chemical and flavor analyses. We will evaluate ClO2 versus common chemical sanitizers (acids, chlorine, peracetic acid, and H2O2) on whole as well as fresh-cut fruits and vegetables. Melons and tomatoes will be inoculated as described above and various times of exposure and ClO2 gas concentrations tested. Fresh-cut lettuce, strawberries and apples inoculated with Salmonella or E. coli O157:H7 will be subjected to various amounts of ClO2 and release rates in packages at different temperatures. Microbial populations will be enumerated during storage.
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Progress:<br/>
2011/10 TO 2012/09<br/>
OUTPUTS: The University of Florida Horticultural Sciences group is investigating the role of ethylene, tissue senescence and chilling injury in the loss of quality during handling of fresh-cut products, with nutritional quality, sensory evaluation and aroma volatile measurement being done in collaboration with Food Science & Human Nutrition and ARS-FL. The survival, proliferation and control of microorganisms on raw material and fresh-cut products are being investigated jointly in FSHN and Plant Pathology. Results of this research were reported to other participants of the S294 Multistate Research Project at the annual project meeting, held in conjunction with the United Fresh Produce Association convention, by poster and by presentation in the Fresh Tech Learning Center. Presentations were also made at professional, scientific society meetings. Information about optimal ripeness stage for processing mangoes into fresh-cut slices and best management practices for fresh-cut mango processing have been disseminated to the industry through the National Mango Board. <br/>PARTICIPANTS: Dr. Jeffrey K. Brecht served as the University of Florida representative on this Multistate Research Project. Drs. Brecht, Donald J. Huber, Steven A. Sargent and Charles A. Sims supervised and conducted research to develop new strategies to improve and better maintain inherent fresh-cut product quality and nutrition, and to improve understanding of physiological mechanisms that affect fresh-cut product quality. Drs. Michelle D. Danyluk, Renee M. Goodrich, Keith R. Schneider, Amarat H. Simonne and Jerry A. Bartz supervised and conducted research to determine critical factors in controlled inoculation studies with human pathogens and surrogates that influence the outcome of quantitative microbial risk assessments, and to evaluate and control unintentional and intentional microbial contamination of intact and fresh-cut produce. Collabortors included Dr. Cecilia Nunes (USF), and Drs. Elizabeth A. Baldwin and Anne Plotto (USDA ARS). Training and professional development was provided to two M.Sc. students, five Ph.D. students and four postdoctoral associates who participated in this project.
<br/>TARGET AUDIENCES: Target audiences were the scientific community and the fresh-cut produce industry, including producers, processors, packaging companies, shipping and other transportation carriers, and retailers. Results were reported at the annual convention of the United Fresh Produce Association, which provided us with a forum to disseminate the results of our research project, and at the S-294 Multistate Research Project annual meeting. Presentations of the results and recommendations from this project were made to professional, academic and commercial audiences.
<br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
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IMPACT: Optimal ripeness stage for processing mangoes into fresh-cut slices (sensory quality) is best predicted by fruit firmness rather than color or compositional. Pink stage tomatoes tolerate 4% but not 6% CO2 at 12.5C, and tolerate 6% CO2 at both 15 and 18C. Analysis of aroma volatiles in order to establish the chilling threshold in terms of aroma inhibition is underway (with ARS-Ft. Pierce). The feasibility of hydrocooling strawberries was demonstrated, allowing sanitization with quality equal to or better than with forced-air cooling. Hot water treatment (2.5 min at 54C or 5 min at 52 C) of MG tomato prior to C2H4 treatment and ripening results in better sensory quality for MG and increased antioxidants and antioxidant capacity for all stage, even with chilling storage at 5 or 12C (with ARS-Ft. Pierce). Fresh-cut processing of postclimacteric papaya caused changes in xyloglucans and polyuronides. 1-MCP had little effect cell wall polymers in fresh-cut tissue. 1-MCP efficacy with fresh-cut tissue will require using fruit processed prior to completion of climacteric-associated cell wall changes. Fresh-cut apple tissue shows high sorption capacity for gaseous 1-MCP, which is reduced after aging or application of the hydroxyl radical quencher hypotaurine. Sorption to aged tissue is enhanced following removal of surface cell layers. Sorption capacity appears to be related to oxidation reactions occurring at the cut surface. Temperature dependent growth models for Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 on fresh-cut celery and melons (cantaloupe, watermelon and honeydew) were constructed. The transfer of pathogens from hands and common kitchen surfaces to and from fresh cut celery, carrots, melon, and leafy greens, and during the simulated washing of cut leafy greens in the home was modeled. Risk factors were evaluated for transfer of Salmonella to tomatoes during harvesting, packing, and shipping, tomato dump and flume tank operations with chlorine dioxide, and alternative harvesting and handling of small fruits. With Salmonella surface inoculation of strawberries at 6.54 log cfu/fruit, forced-air cooling resulted in a slight increase (6.66 logs units), while hydrocooling in 100 ppm NaOCl (7 min) resulted in 2.4 logs decrease. More sanitizer n (200 ppm) decreased Salmonella to 3.07 log cfu/fruit. Storage for 7 d at 2C reduced Salmonella numbers to 5.40 log cfu/fruit, while 100 ppm NaOCl hydrocooled fruit were below detection limit. Retail display (24 h at 25C) after storage caused further reduction of Salmonella in forced-air stored fruit to 4.03 logs and no resuscitation in hydrocooled fruit. Efficacy of water, PAA, ClO2 and NaOCl on Salmonella inoculated tomatoes was tested with an overhead spray brush roller sanitation system. After 5 s, reductions were: PAA 2.8 log CFU/ml, NaOCl, ClO2, and water 1.9 log CFU/ml. There was a 3-log reduction at 15 s, but no further reduction for 30 s except for PAA. PAA had a 1-log unit higher reduction than other sanitizers. At 60 s, log reductions did not differ.