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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED PROCESSES FOR CUCUMBERS, CABBAGE, SWEETPOTATOES, AND PEPPERS TO MAKE HIGH-QUALITY, NUTRITIOUS PRODUCTS AND REDUCE POLLUTION

Location: Food Science Research

2005 Annual Report


1.What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter?
For the pickled and acidified vegetable industry to remain competitive in national and international markets with value-added products from these minor crops, sustained research is needed to improve product quality and develop better processing methods that generate less waste, particularly chlorides from salt. The sweetpotato is also a relatively minor vegetable crop in the U.S. Despite the fact that it is a highly nutritious vegetable, consumption of sweetpotatoes has declined slowly. To increase utilization in the U.S. diet, technologies are needed to convert sweetpotatoes into new forms, such as purees or dehydrated flakes, to be used as ingredients for convenient, value-added products. To assure that sweetpotato products will deliver the high nutritional value that is expected, new cultivars that are introduced need to maintain or increase the levels of carotenoids (orange sweetpotatoes), anthocyanins (purple sweetpotatoes), and phenolic compounds in currently grown cultivars. Processing methods for all of these vegetables need to be developed that minimize losses of components which are beneficial to human health. Microbiological safety has become a critical issue for the acidified foods industry since it has become clear that acid-tolerant pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella) can survive, even though they are unable to grow, in the pH range typical of many acidified vegetables. Microbiological research coordinated with processing and quality research is needed to exclude or kill these pathogens in ways that do not destroy the characteristic properties of current products, and which will allow development of new product types in the future.

Major objectives for this project are: (1) to develop reduced salt fermentation procedures for cucumbers and cabbage; (2) to preserve non-fermented cucumbers and peppers in acidified low salt solutions so they can be stored and used as process-ready ingredients for food products; (3) to develop processing technologies to convert sweetpotatoes into high quality, shelf-stable ingredients, such as purees or dehydrated powders; (4) to increase the content of nutrients and beneficial phytochemicals delivered in vegetable products by cultivar selection and optimization of processing methods; (5) to assure removal of acid-tolerant pathogens from acidified vegetable products in ways that are consistent with production of high quality products.

Customers for this research are farmers who produce vegetables for commercial processing and food processors that develop and manufacture products from cucumbers, cabbage, sweetpotatoes, and peppers. Specific customers include Pickle Packers International, Inc. (a trade association that represents most of the major processors for fermented and acidified vegetables in the United States), The Sweetpotato Council of the United States, and The North Carolina SweetPotato Commission. While commercial food production is the focus of this Unit, through extension programs the results are transferable to home preservation and processing of these vegetables. The research findings benefit the scientific community with new information on the biochemistry of processed vegetables, development of techniques for food fermentations, on mechanisms for killing acid-tolerant pathogens, and analytical techniques for chemical components of vegetables and microorganisms related to processed vegetable products.


2.List the milestones (indicators of progress) from your Project Plan.
FY 2005 1. Determine characteristics of enzymatic and non-enzymatic softening in low salt cucumber fermentations (1). 2. Determine the effect of sodium chloride reduction on texture, flavor, and color of sauerkraut (12). 3. Determine the effect of culture addition on low-salt sauerkraut fermentation (14). 4. Determine the effects of oxygen radicals on softening of peppers and cucumbers (21). 5. Determine microbiological and sensory stability of fresh-cut, refrigerated sweetpotato pieces (24). 6. Determine the dielectric properties and predictive equations for microwave heating of sweetpotato puree (25). 7. Develop predictive equations for microwave heating of sweetpotato puree (26). 8. Evaluate the technical feasibility of microwave sweetpotato puree sterilization with a small-scale microwave processing unit (27). 9. Scale-up microwave processing with pilot-scale microwave unit and evaluate aseptic packaging of microwave-heated puree (28). 10. Determine pre-treatments of sweetpotato purees required to make spray-dried sweetpotato powder (33). 11. Establish appropriate drying parameters for production of spray-dried sweetpotato powder (34). 12. Develop extraction methods for carotenoids, phenolic compounds, and anthocyanins in sweetpotatoes suitable for analysis of several hundred breeding lines each year (39). 13. Determine the survival of Escherichia coli exposed to different food acids (44). 14. Develop mechanistic models to describe the killing effects of acids on acid-tolerant pathogens (46).

FY 2006 1. Evaluate the effect of salt reduction on texture, flavor, and stability of fermented cucumbers (2). 2. Determine the effect of sodium chloride reduction on texture, flavor, and color of sauerkraut (12). 3. Determine the effect of addition of calcium, potassium, and magnesium salts on texture retention, flavor, and color of sauerkraut (13). 4. Determine the effect of low or no added sodium chloride on firmness of preserved small cucumbers (17). 5. Determine optimum combinations of calcium, potassium, magnesium, and alum salts for preservation of firmness in cucumbers and peppers during storage (18). 6. Determine concentrations of sulfite, benzoate, and sorbate required to assure microbial stability in acidified, non-fermented cucumbers and peppers (19). 7. Verify the delivery of a sufficient heat process to all locations in the heating volume of the microwave unit to assure destruction of Clostridium botulinum spores (29). 8. Determine retention of texture, color, flavor, nutrients, and beneficial phytochemicals during storage of microwave-sterilized sweetpotato puree (30). 9. Develop extraction methods for carotenoids, phenolic compounds, and anthocyanins in sweetpotatoes suitable for analysis of several hundred breeding lines each year (39). 10. Develop analytical methods to separate, identify, and quantitate carotenoids, phenolic compounds, and anthocyanins in sweetpotato breeding lines and for evaluation of changes during processing and storage (40). 11. Determine the survival of Escherichia coli exposed to different food acids (44). 12. Determine the survival of Salmonella and Listeria exposed to different food acids (45). 13. Develop mechanistic models to describe the killing effects of acids on acid-tolerant pathogens (46).

FY 2007 1. Evaluate modifications of brining conditions on the dominance of fermentation cultures added to cucumber fermentations (4). 2. Isolate organisms responsible for low-salt spoilage of fermented cucumbers (5). 3. Biochemical and genetic characterization of low-salt spoilage organisms in cucumber fermentations (6). 4. Identify species-specific DNA probes; functional trials of 16S microarrays to detect microbial species in cucumber fermentations (9). 5. Evaluate the microbial ecology of added and natural fermentation microorganisms in laboratory sauerkraut fermentations (15). 6. Determine conditions of low-salt acidified storage which will assure killing of acid-tolerant pathogens in stored cucumbers and peppers (20). 7. Determine the functional performance of microwave-sterilized sweetpotato puree in model food systems (31). 8. Evaluate the quality characteristics of spray-dried sweetpotato powders produced with selected drying conditions (36). 9. Develop analytical methods to separate, identify, and quantitate carotenoids, phenolic compounds, and anthocyanins in sweetpotato breeding lines and for evaluation of changes during processing and storage (40). 10. Determine the effects of processing operations, including peeling, sterilization heating, and spray drying, on the retention of carotenoids, phenolic compounds, and anthocyanins in commercial sweetpotato cultivars (42). 11. Determine the survival of Salmonella and Listeria exposed to different food acids (45). 12. Develop mechanistic models to describe the killing effects of acids on acid-tolerant pathogens (46). 13. Validate models and killing mechanisms by analysis of the die off of pathogens inoculated into acidified vegetable products (47).

FY 2008 1. Evaluate the effects of the addition of calcium, potassium, magnesium, and alum salts on texture, flavor, and stability of fermented cucumbers (3). 2. Determine conditions that prevent growth of low salt spoilage organisms in fermented cucumbers (7). 3. Determine the ecology of laboratory cucumber fermentations (10). 4. Determine changes in cell walls that occur during oxygen-mediated softening of peppers (22). 5. Evaluate the utilization of sterilized sweetpotato puree in selected processed foods (32). 6. Determine the functionality of spray-dried sweetpotato powders in model food systems (37). 7. Evaluate the incorporation of spray-dried sweetpotato powder in selected processed foods (38). 8. Develop models to describe changes in phytochemicals during processing and storage of sweetpotatoes (43). 9. Develop mechanistic models to describe the killing effects of acids on acid-tolerant pathogens (46). 10. Validate models and killing mechanisms by analysis of the die off of pathogens inoculated into acidified vegetable products (47).

FY 2009 1. Fermentation challenge evaluations in low-salt cucumber fermenations (8). 2. Determine the ecology of cucumber fermentations under commercial conditions (11). 3. Determine the microbial ecology of low-salt sauerkraut fermentations under commercial fermentation conditions (16). 4. Determine changes in cell walls that occur during oxygen-mediated softening of peppers (22). 5. Validate models and killing mechanisms by analysis of the die off of pathogens inoculated into acidified vegetable products (47).


4a.What was the single most significant accomplishment this past year?
Continuous microwave sterilization and aseptic packaging of sweetpotato puree.

This is the first report of an aseptically packaged vegetable puree processed by a continuous-flow, microwave heating system. A patent application was filed November 12, 2004. Further studies are in progress to validate the process for microbial safety, as well as to expand its application to other fruit and vegetable purees. This technology provides a new process to convert sweetpotatoes and other highly nutritious fruits and vegetables into shelf-stable functional ingredients suitable for use in a variety of formulated food products. Expansion of the market for sweetpotato puree would provide farmers with a market for 40% of the sweetpotato crop, which currently is left in the field because of small size or poor shape that makes them unsuitable for sale.


4b.List other significant accomplishments, if any.
Protection of Escherichia coli O157:H7 at low pH by organic acids.

Escherichia coli O157:H7 is a pathogen that can survive for extended periods in acid and acidified foods with pH less than 4.0. Research was directed to determine the relationship between the amount of an added food acid such as acetic acid, lactic acid, malic acid, and citric acid on the rate of death of E. coli at pH 3.2. The expectation was that, as more of an acid was added, E. coli would die off faster. Instead of this result, it was found that low concentrations of lactic acid, acetic acid, and malic acid reduced the rate of E. coli death, and only at higher concentrations did they increase the death rate beyond that which occurred without the added organic acid. D-lactic acid, one of two naturally occurring forms of lactic acid, was remarkable because, starting at a very low concentration (0.009%) up to 0.18%, it nearly stopped die off of E. coli cells for 6 hr at pH 3.2. This is the first case in which organic acids have been found to protect a pathogenic organism within the pH range of acid and acidified foods, such as fruit juices and pickled vegetables. This observation highlights the need to better understand the mechanisms by which food acids inhibit and kill bacteria. These observations were done in air and so may be relevant to surface treatments of foods with organic acids. It will also be important to determine the killing effects of organic acids in the absence of air, such as occurs when products are packaged in hermetically sealed containers.


4c.List any significant activities that support special target populations.
None


5.Describe the major accomplishments over the life of the project, including their predicted or actual impact.
Continuous microwave sterilization and aseptic packaging of sweetpotato puree.

This is the first report of an aseptically packaged vegetable puree processed by a continuous-flow, microwave heating system. A patent application was filed November 12, 2004. Further studies are in progress to validate the process for microbial safety, as well as to expand its application to other fruit and vegetable purees. This technology provides a new process to convert sweetpotatoes and other highly nutritious fruits and vegetables into shelf-stable functional ingredients suitable for use in a variety of formulated food products. Expansion of the market for sweetpotato puree would provide farmers with a market for 40% of the sweetpotato crop, which currently is left in the field because of small size or poor shape that makes them unsuitable for sale.

Protection of Escherichia coli O157:H7 at low pH by organic acids.

Escherichia coli O157:H7 is a pathogen that can survive for extended periods in acid and acidified foods with pH less than 4.0. Research was directed to the determination of the relationship between the amount of an added food acid such as acetic acid, lactic acid, malic acid, and citric acid on the rate of death of E. coli at pH 3.2. The expectation was that as more of an acid was added, E. coli would die off faster. Instead of this result, it was found that low concentrations of lactic acid, acetic acid, and malic acid reduced the rate of E. coli death, and only at higher concentrations did they increase the death rate beyond that which occurred without the added organic acid. D-lactic acid, one of two naturally occurring forms of lactic acid, was remarkable because, starting at a very low concentration (0.009%) up to 0.18%, it nearly stopped die off of E. coli cells for 6 hr at pH 3.2. This is the first case in which organic acids have been found to protect a pathogenic organism within the pH range of acid and acidified foods, such as fruit juices and pickled vegetables. This observation highlights the need to better understand the mechanisms by which food acids inhibit and kill bacteria. These observations were done in air and so may be relevant to surface treatments of foods with organic acids. It will also be important to determine the killing effects of organic acids in the absence of air, such as occurs when products are packaged in hermetically sealed containers.


6.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?
Continuous microwave sterilization and aseptic packaging of sweetpotato puree was presented at a trade organization meeting. Potential processors are aware of the development of this technology and have expressed interest in using the technology. Information on time/temperature relationships to assure killing of Escherichia coli, Salmonella, and Listeria in acidified vegetables was published in a peer-reviewed journal and presented at a GMP Acidified Foods training for people from the U.S. and other countries who supervise commercial processing of acidified foods. Information on the ability of certain food acids to slow the rate of killing Escherichia coli was presented at a scientific meeting. Information on the numbers of microorganisms in fresh cucumbers and their distance from the surface of the cucumber fruit was published in a peer-review journal. This information will be helpful to scientists in determining the distance inside a fruit a sanitation treatment must reach to be effective.


7.List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below).
Presentations: McFeeters, R.F. 2005. Research results and new directions for the USDA-ARS Food Science Research Unit. PPI Board of Directors Meeting. Manzanillo, Mexico.

Truong, V.D. 2005. New developments in sweetpotato processing technologies. Invited talk at the Annual Meeting of the NC Sweetpotato Commission, Wilson, NC.

Bjornsdottir, K., McFeeters, R.F., Breidt, F. 2005. Killing effects of organic acids independent of pH on Escherichia coli K12. ASM meeting, Atlanta, GA.

McFeeters, R.F. 2005. Preservation of texture of acidified red bell peppers. 17th International Pepper Conf., Naples, FL.

Grabowski, J.A., Truong, V.-D. 2005. Processing of sweetpotato powders by spray-drying. National Sweetpotato Collaborators Group.

Johanningsmeier, S.D., Thompson, R.L., Fleming, H.P., McFeeters, R.F. 2005. Starter culture addition to cabbage fermentations decreases variability and increases the quality of reduced salt sauerkraut. Institute of Food Technologists meeting.

Teow, C.C., Truong, V.-D., McFeeters, R.F., Yencho, G.C. 2005. Total antioxidant activity of sweetpotato cultivars with varying flesh colors. Institute of Food Technologists.

Maruvada, R., McFeeters, R. F. 2005. Role of enzymatic activity in softening of fermented cucumbers. American Chemical Society meeting.


Review Publications
Breidt, F., Hayes, J.S., Osborne, J.A., McFeeters, R.F. 2005. Determination of 5-log pathogen reduction times for heat-processed, acidified vegetable brines. Journal of Food Protection. 68:305-310.

Johanningsmeier, S.D., Fleming, H.P., Thompson, R.L., McFeeters, R.F. 2005. Chemical and sensory properties of sauerkraut produced with Leuconostoc mesenteroides starter cultures of differing malolactic phenotypes. Journal of Food Science. 70:S343-S349.

Lu, Z., Altermann, E., Breidt, F., Predki, P., Fleming, H.P., Klaenhammer, T.R. 2005. Sequence analysis of the Lactobacillus plantarum bacteriophage phi JL-1. Gene. 348:45-54.

Johanningsmeier, S.D., Fleming, H.P., Breidt, F. 2004. Malolactic activity of lactic acid bacteria during sauerkraut fermentation. Journal of Food Science. 69:M222-M227.

Passos, F.V., Felder, R.M., Fleming, H.P., McFeeters, R.F., Ollis, D.F. 2004. Dynamic model for mass transfer of solutes in cucumber fermentation. Journal of Food Engineering. 68:297-302.

Reina, L.D., Breidt, F., Fleming, H.P., Kathariou, S. 2005. Isolation and selection of lactic acid bacteria as biocontrol agents for nonacidified, refrigerated pickles. Journal of Food Science. 70:M7-M11.

Mattos, F.R., Fasina, O.O., Reina, L.R., Fleming, H.P., Breidt, F., Damasceno, G.S., Passos, F. 2005. Heat transfer and microbial kinetics modeling to determine the location of microorganisms within cucumber fruit. Journal of Food Science. 50(5):E324-E330.

Last Modified: 7/24/2014
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