2010 Annual Report
1a.Objectives (from AD-416)
Our objectives are to: (1) develop reduced salt fermentation procedures for
cucumbers and cabbage that will consistently produce vegetables with firm texture
and appropriate flavor; (2) preserve non-fermented cucumbers and peppers in
acidified, low-salt, or salt-free solutions so they can be stored and used as
process-ready ingredients for food products; (3) develop processing technologies to convert sweetpotatoes into shelf-stable ingredients, such as puree and dehydrated powder, with physical, chemical, and sensory properties suitable for use as ingredients in restructured and formulated food products; (4) increase nutrients and beneficial phytochemicals in sweetpotato products by selection of cultivars with increased concentrations of target components and by optimization of processing conditions to minimize losses. Additional funds in support of project plan objectives 1,2,5: (1) to determine the metabolic changes that lead to the death of vegetable fermentation bacteria in response to acid and to develop approaches to assure growth of desirable fermentative organisms; (2) to understand and prevent degradation of the cell wall structure that results in softening of fermented and acidified vegetabes stored in low salt without thermal treatments.
1b.Approach (from AD-416)
New or improved processing methods will be developed for cucumbers, cabbage, peppers and sweetpotatoes that will increase utilization of these vegetables. Research will be done both to solve problems that limit utilization and to create opportunities to broaden uses for these vegetables as ingredients in formulated foods. Problems to be addressed include excessive generation of processing wastes, loss of quality attributes, and inadequate commercial shelf-life. Opportunities include development of new convenient-to-use ingredient forms for these vegetables and enhancement of the nutrient and beneficial phytochemical levels in products produced from these vegetables. Control of texture is a major quality issue that must be addressed in the development of improved processing methods. Therefore, the basic mechanisms which accelerate and inhibit softening of cucumbers, peppers, and cabbage will be investigated, as well as the factors that modify the rheology of sweetpotato puree. A recent development by this unit of an experimental technique to experimentally separate the effects of hydrogen ions from the effects of protonated acids on killing bacteria will be exploited to further our understanding of the physiology of acid tolerance in fermentative bacteria.
Continued investigations of the microbiology and biochemistry of the spoilage of fermented cucumbers. Identified three yeasts, two lactic acid bacteria, and two clostridial species from commercial fermented cucumber tanks that spoiled. The involvement of these organisms in the spoilage process was confirmed by recreation of spoilage after inoculation of fermented cucumbers with the isolated organisms. Biochemical changes caused by lactic acid bacteria that grow during the anaerobic stage of the spoilage were characterized in filter sterilized fermented cucumber slurries inoculated with mixed spoilage microorganisms. The only pH/salt combination that resulted in no spoilage was pH 3.2/6.0% NaCl. Spoilage was observed at all higher pH and lower salt concentrations that were tested. Changes in non-volatile low molecular weight metabolites from selected spoilage conditions were determined by derivatization of the metabolites so they became volatile, followed by two dimensional gas chromatography-mass spectrometry. Initiated an investigation of the shelf life of dill pickles in newly developed pasteurizable plastic jars compared to glass jars. Product stored in plastic containers with different oxygen permeability will be evaluated by a trained sensory panel. Differences in volatile components compared to products stored in glass containers will be determined by two dimensional gas chromatography-mass spectrometry. Developed a procedure to grow large populations of Lactobacillus plantarum in jars of pasteurized dill pickles for use as a starter culture in pilot scale and commercial cucumber fermentation tanks. The culture can be produced such that it is suitable for use in the production of pickle products that are kosher certified. Investigated procedures to maintain intact sweetpotato cubes during continuous microwave processing to achieve commercial sterility. Sweetpotato cubes did not disintegrate after a two step pre-treatment that included a one hour soak in 0.25% sodium carbonate at 25 degrees C followed by a one hour soak in 1% calcium chloride at 60 degrees C.
Naturally occurring preservative compounds to prevent growth of microorganisms in acidified vegetables. Sulfite and sodium benzoate are the primary preservatives used to prevent the growth of spoilage lactic acid bacteria and yeasts in bulk-stored or consumer size containers of pickled vegetables that are not heat processed. However, some consumers avoid products that contain either of these traditional preservatives. ARS scientists located at the Food Science Research Unit in Raleigh, NC have been able to preserve acidified cucumbers by using a combination of two naturally occurring compounds. Fumaric acid has been found to inhibit growth of spoilage lactic acid bacteria, while allyl isothiocyanate, the ‘hot’ flavor in mustard oil, is effective in preventing growth of spoilage yeasts. Fumaric acid is a normal metabolite of all plant and animals and has GRAS status as a food ingredient. Used in combination these components prevented spoilage of cucumbers acidified with vinegar to pH 3.6 or lower. Due to the strong flavor of AITC there will be a limited range of products in which it can be used, so it will be useful in the future to identify other natural compounds that can serve as complimentary preservatives with fumaric acid.
Lu, Z., Altermann, E., Breidt, F., Kozyavkin, S. 2010. Sequence analysis of Leuconostoc mesenteroides bacteriophage (phi)1-A4 isolated from industrial vegetable fermentation. Applied and Environmental Microbiology. 76(6):1955-1966.
McFeeters, R.F., Perez Diaz, I.M. 2010. Fermentation of cucumbers brined with calcium chloride instead of sodium chloride. Journal of Food Science. 75(3):C291-C296.
Truong, V., Deighton, N., Thompson, R.L., Mcfeeters, R.F., Dean, L.L., Pecota, K.V., Yencho, G. 2010. Characterization of anthocyanins and anthocyanidins in purple-fleshed sweetpotatoes by HPLC-DAD and LC-ESI/MS-MS. Journal of Agriculture and Food Chemistry. 58:404-410.
Perez Diaz, I.M., Mcfeeters, R.F. 2010. Preservation of acidified cucumbers with a natural preservative combination of fumaric acid and allyl isothiocyanate that target lactic acid bacteria and yeasts. Journal of Food Science. 75(4):M204-M208.
Barth, M., Hankinson, T.R., Zhuang, H., Breidt, F. 2009. Microbiological spoilage of fruits and vegetables. In: Compendium of the microbiological spoilage of fruits and vegetables. p. 135-183.
Olsen, M., Perez Diaz, I.M. 2009. Influence of microbial growth in the redox potential of fermented cucumbers. Journal of Food Science. 74(4):M149-M153.
Truong, V., Avula, R.Y. 2010. Sweetpotato purees and powders for functional food ingredients. In: Ray, R.C., Tomlins, K.I., editors. Sweetpotatoes: Post-harvest Aspects in Food, Feed and Industry. New York: Nova Science Publishers, Inc. p. 117-161.