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United States Department of Agriculture

Agricultural Research Service


Location: Food Science Research

2009 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.

3.Progress Report
Continued pilot plant scale research at a commercial processing facility to do salt-free cucumber fermentations by brining with calcium chloride to maintain cucumber firmness. Focus was to minimize yeast growth in the no salt environment. Experiments to reproduce spoilage with organisms isolated from commercial spoilage were partially successful because lactic acid is degraded by the isolated, but not to the extent that occurs in spoilage outbreaks. Redox potentials were measured in commercial fermentation tanks of different processors. Three patterns of redox potential changes during fermentation have been identified with normal fermentations, fermentations in which a secondary yeast fermentation occurs, and fermentations which spoil. Investigated replacement of traditional preservatives (sodium benzoate, sodium metabisulfite) with fumaric acid in combination with plant flavor extracts that have antimicrobial activities for preservation of acidified vegetables without fermentation or a heat process. Investigated the microbial ecology when fermented cucumbers are exposed to excessive aeration as a result of air purging tanks to prevent boating damage. Did an initial project to identify metabolites and determine those that change in fermentations using two dimensional gas chromatography/time-of-flight mass spectrometry. Initiated research to do microwave processing of sweet potato chunks added to sweetpotato puree to broaden the range of products that are suitable for microwave sterilization.

This project terminated at its scheduled date of 7/28/2009 and has been replaced by bridging project #6645-41000-006-00D pending scientific review.

1. Aseptic processing of purple-fleshed sweetpotato purees. Demonstrated an application of continuous-flow microwave sterilization for processing shelf-stable purees from purple-fleshed sweetpotatoes. The sterilized puree was cooled and filled into aseptic pouches. This puree had superior quality as compared to canned puree. With high retention of color, anthocyanin content and antioxidant activity, the purple-fleshed sweetpotato puree processed by the microwave heating technology can be used as a functional food ingredient in various processed food products.

Review Publications
Yencho, G., Pecota, K.V., Schultheis, J.R., Pesic-Vanesbroeck, Z., Holmes, G.J., Little, B.E., Thornton, A.C., Truong, V. 2008. ‘Covington’ sweetpotato. HortScience. 43(6):1911-1914.

Steed, L.E., Truong, V., Simunovic, J., Sandeep, K.P., Kumar, P., Cartwright, G.D., Swartzel, K.R. 2008. Continuous flow microwave-assisted processing and aseptic packaging of purple-fleshed sweetpotato purees. Journal of Food Science. 73(9):E455-E462.

Maruvada, R., McFeeters, R.F. 2009. Evaluation of enzymatic and non-enzymatic softening in low salt cucumber fermentations. International Journal of Food Science and Technology. 44:1108-1117.

Neta, E., Johanningsmeier, S.D., Drake, M., McFeeters, R.F. 2009. Effects of pH adjustment and sodium ions on sour taste intensity of organic acids. Journal of Food Science. 74(4):S165-S169.

Perez Diaz, I.M., McFeeters, R.F. 2009. Modification of azo dyes by lactic acid bacteria. Journal of Applied Microbiology. 107:584-589.

Perez Diaz, I.M., Truong, V., Webber, A.M., McFeeters, R.F. 2008. Microbial growth and the effects of mild acidification and preservatives in refrigerated sweetpotato puree. Journal of Food Protection. 71(3):639-642.

Last Modified: 7/23/2014
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