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United States Department of Agriculture

Agricultural Research Service


Location: Food Science Research

2013 Annual Report

1a. Objectives (from AD-416):
1. Develop approaches for commercial cucumber fermentations without the use of sodium chloride that will prevent development of post fermentation microbiological spoilage and retain the quality of cucumbers during storage. 2. Increase consumer acceptance of acidified vegetables that are refrigerated or preserved at ambient temperature without a thermal process by use of alternative acids and natural antimicrobial compounds to replace traditional preservatives, and by addition of pro-biotic lactic acid bacteria that provide health benefits to consumers. 3. Evaluate the use of newly developed pasteurizable plastic containers and alternative approaches to heating acidified vegetables in hermetically sealed containers, including microwave heating technologies, to reduce the energy input required to manufacture safe, high quality acidified vegetable products and deliver them to consumers. 4. Develop a new vortex dehydration technology to convert sweetpotatoes and sweetpotato by-products into functional ingredients to be used in processed food products. 5. Evaluate advanced sweetpotato genotypes intended for processing applications, postharvest handling systems, and processing technologies for their potential to increase levels of beneficial phytochemicals in concert with production of high quality food products.

1b. Approach (from AD-416):
The acidified and fermented vegetable industry must address issues of: (1) excessive chloride waste from high salt fermentations, (2) high energy consumption from the use of 50 year old steam pasteurization technology, and (3) static or declining consumption of traditional product lines. For sweetpotatoes to make a greater contribution to the U.S. diet, they must be converted into forms that maintain or increase nutrient levels and that can be conveniently used by food processors in a variety of food products. To reduce chloride waste, methods to do commercial cucumber fermentations without use of sodium chloride will be developed. Reduction of energy consumption will be addressed by using microwave heating to more efficiently deliver heat to products and by developing practical means to pre-heat product and brine prior to filling containers. More convenient packaging, alternatives to traditional preservatives, acidification of nutrient rich vegetables to reduce sour taste intensity, and procedures to deliver probiotic bacteria will be developed to provide new approaches to add value to fermented and acidified vegetable products. Sweetpotato farmers and processors need new processing approaches that will result in increased production and consumption of this highly nutritious vegetable. A new vortex dehydration technology will be evaluated to determine if it can be used to produce high quality dehydrated sweetpotato flours from orange and purple flesh sweetpotatoes which can serve as functional food ingredients. There will be continued coordination with sweetpotato breeding programs to develop cultivars better adapted to year round production of sweetpotato fries and chips.

3. Progress Report:
Progress was made on all five objectives. Under objectives 1 and 2, the second-year evaluation on microbiological stability of commercial scale calcium chloride (CaCl2) fermentations, to replace the traditional high salt process, was successfully conducted by incorporating preservatives after the completion of primary fermentation. The minimal inhibitory concentrations of selected preservatives to prevent microbial spoilage in NaCl free fermentations were determined. Although residual CaCl2 in the fermented cucumbers was able to retard product degradation during storage, maintaining the texture of the whole fruits during long term bulk storage was a challenge. Consumer testing indicated that reduced texture of finished products was more important to overall acceptability than the amount of residual CaCl2 in the pickle chips up to the legal limit of 0.4%, and the taste threshold of CaCl2 in hamburger dill chips was found to be greater than 0.4% for 90% of the population. Development of a new low energy technology for the in-house production of Kosher starter cultures was initiated. Studies of the microbial ecology and biochemical pathways involved in commercial scale, spoilage-associated secondary cucumber fermentations were conducted. Semi-commercial scale trials to evaluate the ability of fumaric acid and allyl isothiocyanate, the spicy component in horseradish and mustard, to preserve acidified cucumbers in reduced salt cover brines were completed. A combination of sodium benzoate and fumaric acid was effective in preventing microbial spoilage with adequate texture and color retention. A 5-log reduction for bacterial pathogens (E. coli O157:H7) could be achieved for cucumber preservation formulations containing sulfite, benzoate, fumaric acid, allyl isothiocyanate, and lauric arginate. Technology transfer activities for the low salt and acid preservation method were initiated. Under objective 3, a patentable novel method to evaluate and determine inactivation of biological substances in food materials was developed. This method has proven useful in the microbiological validation of continuous flow microwave processing of vegetables and fruits and may also be used for determination of process deviations and quality of selected processed foods. For sweetpotatoes (Objectives 4 and 5), good quality flours with over 85% beta-carotene retention can be produced using a vortex dehydration system operated with compressed air of 350 cubic ft/min and 110°C. Raising the temperature above 110°C resulted in carotene isomerization and decrease in beta-carotene retention. A cyclone and other devices for collecting the flours coming out of the vortex system was fabricated and being evaluated for the effect of the configuration on the air flow velocity within the system. Progress has been made in identifying potential sweetpotato clones with yellow and orange fleshed color from the breeding programs on sugar profiles, dry matter content, oil absorption and fried product quality. Over 350 sweetpotato clones were evaluated and 15 promising clones were recommended for sending to food companies for further evaluation of attributes for French fry processing.

4. Accomplishments
1. Commercial scale inception of the newly developed sodium chloride free cucumber fermentation technology. Current chloride discharge limits imposed by regulatory agencies on cucumber pickling companies has made the adoption of a reduced sodium chloride technology an urgent need. Sodium chloride salt plays a critical role in the traditional process for establishing the correct microflora for fermentation, retention of high quality texture attributes, and microbial stability during bulk storage. The documented effect of low concentrations of calcium ions in cucumber firmness retention led to the proposed fermentation of the fruits in calcium chloride brines as a replacement for sodium chloride. Development of a calcium chloride fermentation system in closed jars revealed that fermentation in calcium chloride brines requires the use of a starter culture, and tissue firmness was similarly retained in the calcium chloride brined fruits during long-term storage as compared to the sodium chloride counterpart. Translation of this sodium chloride-free fermentation system to the large, open-top tanks in the commercial environment presents an alternative for processors to reduce the environmental impact of their operations. About 40 commercial tank trials have been performed to date applying the calcium chloride fermentation cover brine solution and starter culture approach tested in the laboratory. The number of commercial tanks programmed for packing with the calcium chloride cover brine formulation this season will quadruple that of the experimental trials, allowing processors to maintain a functional tank yard this year while complying with environmental regulations. It is expected that this new technology will be fully implemented in the next couple of years generating up to $489,000 cost savings annually and preventing the disposal of tons of sodium chloride into waste water streams annually.

Review Publications
Breidt, F., McFeeters, R.F., Perez Diaz, I.M., Lee, C. 2012. Fermented Vegetables. In: Doyle, M.P., Buchanan, R.L., editors. Food Microbiology: Fundamentals and Frontiers, 4th Ed. Washington, D.C.: ASM Press. p. 841-855.

Franco, W., Perez-Diaz, I.M. 2012. Development of a model system for the study of spoilage associated secondary cucumber fermentation during long term storage. Journal of Food Science. 77(10):M586-M592.

Maloney, K.P., Truong, V.D., Allen, J.C. 2012. Chemical optimization of protein extraction from sweet potato (Ipomoea batatas) peel. Journal of Food Science. 77(11):E307-E312.

Shi, Q., Vitchuli, N., Nowak, J., Jiang, S., Caldwell, J.M., Breidt, F., Bourham, M., Zhang, X., Mccord, M. 2013. Multi-functional and durable nanofiber-fabric layered composite for protective application. Journal of Applied Polymer Science. 128(2):1219-1226.

Perez-Diaz, I.M., Franco, W. 2013. Microbial interactions associated with secondary cucumber fermentation. Journal of Applied Microbiology. 114:161-172.

Breidt, F., Medina-Pradas, E., Wafa, D., Perez Diaz, I.M., Franco, W., Huang, H., Johanningsmeier, S.D., Kim, J. 2013. Characterization of cucumber fermentation spoilage bacteria by enrichment culture and 16S rDNA cloning. Journal of Food Science. 78(3):M470-M476.

Perez Diaz, I.M. 2013. Putative and unique gene sequence utilization for the design of species specific probes as modeled by Lactobacillus plantarum. Current Microbiology. 66:266-270.

Koskiniemi, C.B., Truong, V., McFeeters, R.F., Simunovic, J. 2013. Effects of acid, salt and soaking time on the dielectric properties of acidified vegetables. International Journal of Food Properties. 16:917-927.

Nawalakhe, R., Shi, Q., Vitchuli, N., Noar, J., Caldwell, J.M., Breidt, F., Bourham, M.A., Zhang, Z., Mccord, M.G. 2013. Novel atmospheric plasma enhanced chitosan nanofiber/gauze composite wound dressings. Journal of Applied Polymer Science. 129(2):916-923.

Johanningsmeier, S.D., McFeeters, R.F. 2013. Metabolism of lactic acid in fermented cucumbers by Lactobacillus buchneri and related species, potential spoilage organisms in reduced salt fermentations. Food Microbiology. 35(2):129-135.

Koskiniemi, C.B., Truong, V., McFeeters, R.F., Simunovic, J. 2013. Quality evaluation of packaged acidified vegetables subjected to continuous microwave pasteurization. LWT - Food Science and Technology. 54:157-164.

Last Modified: 06/22/2017
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