Food Safety, Waste Minimization, and Value Enhancement of Fermented and Lightly Processed Vegetables

Methods will be developed to enhance the microbiological safety of refrigerated, mildly or non-acidified, pickled vegetables by using modern molecular biology and predictive microbiology techniques. The use of selected and potentially modified cultures of lactic acid bacteria and natural plant antimicrobial compounds will be evaluated as biocontrol agents to preclude growth of pathogenic bacteria such as Listeria under refrigerated conditions. Fundamental studies on the chemistry of fresh, stored, processed vegetables will be done to optimize the sensory and nutritional quality and safety of products for human consumption. Methods for studying changes in volatile flavor compounds of fresh, fermented, and stored vegetables will be developed, as will methods to retard off-flavor development. Improved methods will be developed for the bulk preservation of brined fermented vegetables such as cucumbers, cabbage, and peppers so as to reduce salt and other wastes, improve quality, and assure greater uniformity.
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PROGRESS: 2002/10 TO 2003/09<br>
1. What major problem or issue is being resolved and how are you resolving it? Food safety has become of increasing concern with fresh and minimally processed vegetables in recent years. We are contributing to resolving food safety problems in such products by: <ol> <li>developing biocontrol systems involving use of competitive inhibition of pathogens with harmless lactic acid bacteria,
<li>developing washing and minimal blanching treatments to remove or inactivate pathogens, and
<li>determining how phytochemicals can be used to inhibit growth of pathogens.</ol>
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Waste minimization in the bulk storage of brined vegetables is necessary for processors to meet regulatory guidelines for discharge of processing effluents. We are attempting to solve the waste problem by developing methods for preserving brined vegetables that minimize or eliminate processing wastes. It is intended that such products are process-ready when received by the processor, with no need to wash out excess salt. Value enhancement of fermented and lightly processed vegetables is needed to increase the profitability of farmers and processors. Methods being developed for process-ready brined vegetables may offer value enhancement and a market hedge to the farmer, and a more uniform and higher value product with reduced waste to the processor. Annual per capita consumption of sweetpotato has declined from 25 to less than 5 pounds today. New, value-added products are being developed from this nutritious vegetable.
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2. How serious is the problem? Why does it matter? Food safety - While the safety of foods produced in this country is considered to be among the best in the world, several instances of food poisoning from consumption of vegetable products have occurred in recent years. This has occurred during a period of increasing imports of vegetables from foreign countries. Our improved technology can be applied to imported vegetables as well. However, increasing imports are causing added pressures on our farmers and processors to compete more aggressively on an international level. Waste minimization - Some commercial U.S. firms have been forced out of business, and others are having difficulty meeting regulatory guidelines for chloride disposal. It is necessary that our farmers/processors be provided with improved technology for preserving brined produce in order for them to compete with imports from countries with lower environmental standards. Value enhancement - Profitability is a continuing goal of our agricultural system, which our research on process-ready brined vegetables is intended to accomplish for the produce industry at the farm and processor levels. Fruits and vegetables are highly recommended components of our diets. The sweetpotato is a particularly nutritious, but underutilized vegetable. However, products must be made available in forms that attract attention of the consumers.
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3. How does it relate to the National Program(s) and National Program Component(s) to which it has been assigned? This project relates to food processes and products (4.1.2.3) and bacteria and viruses (4.2.1.3). This project also relates to NP 108 (Food Safety) and NP 306 (Quality and Utilization of Agricultural Products). We are developing improved processes to increase the quality, safety, nutritional quality, and value of food products, to increase processing efficiency, and to reduce wastes of fresh and processed vegetable products related to commodities such as cucumbers, cabbage, peppers, and sweetpotatoes.
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4. What were the most significant accomplishments this past year? A. Single Most Significant Accomplishment During FY 2003 Red bell pepper is a high value vegetable that is used as an ingredient in a variety of processed foods, but it is susceptible to rapid softening when it is preserved in acidified brine solutions. Storage conditions to reduce the rate of softening of red bell peppers stored in a salt-free vinegar solution with sulfite as a microbial preservative were established by the Food Science Research Unit (Raleigh, NC). The major factors that had to be controlled were blanching the fresh tissue at 167 deg F, maintaining the pH near 3.5 in 0.9% vinegar, and adding 0.1% calcium chloride. Results of this work can be used to increase the shelf- life of stored peppers. B. Commercially sauerkraut is made by natural fermentation that is subject to considerable lot-to-lot variation because of the variability in cabbage and naturally occurring microorganisms. An investigation was done to establish in detail the microbial ecology of normal commercial fermentations by the Food Science Research Unit. Twenty-six distinct bacteriophages were identified that attacked 28 strains of lactic acid bacteria that increase and die off during the course of a normal sauerkraut fermentation. Two bacteriophages were found that attacked different species of lactic acid bacteria. These results show a previously unrecognized dimension of the sauerkraut fermentation that will have to be taken into account in efforts to reduce the salt required in this fermentation. Homofermentative lactic acid bacterial cultures need to be added to assure consistent cucumber fermentations under reduced salt conditions. A bacteriophage was isolated and characterized that attacks a strain of Lactobacillus plantarum that is being developed as a bacterial culture for these fermentations. The genome sequence of this phage was obtained and analyzed by the Food Science Research Unit in collaboration with the North Carolina State University, Dept. of Food Science. Understanding the genetic capabilities of this bacteriophage may aid the development of techniques to control its effect on fermentations.
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5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. A system was designed and equipment constructed for development of the bag-in-box concept for bulk preservation of brined cucumbers and other vegetables with minimum waste generation. This system has been tested over the past two years, and various box and bag designs have been evaluated. If successfully applied, the concept stands to benefit the farmer (value addition; market hedge) and the processor (minimum waste; higher, more uniform quality) of pickled vegetables. Processing and storage conditions to reduce the rate of softening of red bell peppers have been determined. This will help processors maintain quality of this high value vegetable during storage in acidified brines. The effect of storage pH on the production of fresh cucumber flavor compounds during storage of non-acidified refrigerated cucumbers has been determined. This will aid processors in assessment of the shelf life of this product. A procedure to make restructured sweetpotato fries and patties has been developed to increase the utilization of processed sweetpotato products. A patent has been issued for this process. Modeling of the growth of bacteria has been done to understand the factors that affect their growth and death in vegetable fermentations. A competitive growth model was developed to investigate the factors that determine whether Listeria monocytogenes, a pathogen, or a biocontrol bacterium, Lactococcus lactis, will dominate growth at refrigerated abuse temperatures. An energy-based model was developed to predict the growth of L. lactis under conditions of fluctuating temperatures.
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6. What do you expect to accomplish, year by year, over the next 3 years? 2004 Expected Accomplishments Determination of the changes in cell walls that lead to rapid loss of texture when peppers are exposed to oxygen during acidified storage. Continue research to define acid concentrations, pH, temperature, and time required to assure removal of pathogens during acidified storage of different vegetables. Comparative analysis of the Leuconostoc mesenteroides genome with the genomes of other lactic acid bacteria. Quantitative evaluation of the distribution of phenolics and carotenoids in the roots of commercial sweetpotato cultivars. Determination of the effects of peeling and thermal processing methods on the retention of these compounds and antioxidant activities in sweetpotato purees. 2005 Expected Accomplishments Identify bacteria responsible for anaerobic spoilage of cucumbers fermented with low salt concentrations. Determine the genes involved in acid resistance of lactic acid bacteria and the genetic regulation of the response of lactic acid bacteria and acid-tolerant pathogenic bacteria in foods to environmental stress. Development of processing ingredients or methods to extend the shelf-life of acidified vegetables in plastic containers with significant oxygen permeability. Develop models that will allow the prediction of the amounts and kinds of acids needed to achieve desirable levels of sourness in acidified vegetable products. Application of microwave energy in continuous-flow processing and aseptic packaging of purees from sweetpotatoes and other vegetables. Evaluation of the rheological properties, sensory quality, and microbial safety of microwaved processed purees.
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2006 Expected Accomplishments Identification of the components of peppers that inhibit the growth of spoilage microorganisms and/or kill pathogenic bacteria that may survive low pH conditions. Development of procedures to obtain consistent high quality sauerkraut in reduced salt fermentation conditions. Isolation and quantification of anthocyanin components in sweetpotatoes and determination of the functional properties of sweetpotato anthocyanins in food systems. Use genome sequence data to develop methods for identifying and characterizing bacteria in vegetable fermentations and low salt spoilage fermentations that do not require culturing the bacteria. Determine the genes of lactic acid bacteria that allow these organisms to predominate in mixed culture with pathogenic bacteria in foods.
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7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Information on how to maintain the firmness of pepper tissue during acidified storage was presented at national meetings of acidified foods processors. In addition, progress on low salt fermentation of cucumbers and the effect of pH, temperature, and the type of acid on the death rate of acid-resistant pathogenic Escherichia coli were presented at these meetings. Continued to provide basic information on the principles for safe preservation of acidified foods by having scientists in the Unit teach portions of an annual Acidified Foods GMP School to industry personnel. Scientists in the Unit consulted with the Research and Development Committee of Pickle Packers International, Inc., to develop recommendations for assuring removal of acid-resistant pathogenic bacteria from commercial pickled vegetable products. Scientists in the Unit have had numerous consultations with companies and individuals to provide information and recommendations regarding the processing of acidified vegetables, sauerkraut and cucumber fermentations, and sweetpotatoes. 8. List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: This does not replace your peer-reviewed publications listed below). Breidt, Jr., F. The ecology of bacteria and bacteriophage from commercial vegetable fermentations. 2003. International Union of Food Science and Technology. Paper No. SY11-2. McFeeters, R.F. Fermentation microorganisms and flavor volatile changes in fermented foods. International Union of Food Science and Technology. Paper No. SY11-4.