2011 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.
Studied cucumber fermentations without the use of sodium chloride aiming reducing energy use and pollution. Calcium chloride fermentation resulted in higher volume and fruit yields which were also more easily processed into finished products as compared to table salt fermentation. Efforts to develop a suitable starter culture to obtain appropriate lactic acid fermentation in calcium chloride tanks revealed that the ideal bacterial culture should contain a combination of Lactobacillus plantarum and L. brevis. The study on fermented cucumber spoilage showed that while the bacterium, L. buchneri and selected oxygen dependent yeasts can initiate an increase in the post-fermentation pH and render the product unsafe for consumption, the yeasts are more prone to complete this task faster than the bacterium. An experimental model system was developed to follow microbiological growth during spoilage and the profiles of volatiles and nonvolatile metabolites using two dimensional gas chromatography-mass spectrometry will lead to the identification of suitable preventive strategies. Successfully isolated microorganisms implicated in fermented cucumber spoilage rendering the creation of a 16S rRNA library unnecessary for the completion of future objectives. A new preservative, lauric arginate, effectively prevented the growth of the bacteria responsible for cucumber fermentation and selected yeasts capable of inducing pH increases and forming a film on the surface of the commercial tanks. A method was developed to assure the survival of a probiotic culture in a refrigerated pickle product, and may open new markets for US pickle products. Fresh-pack products packed in pasteurizable plastic containers were evaluated by sensory and chemical analysis during storage. Future efforts will need to focus on reducing scalping and oxidation of flavor compounds if plastic packaging is to be useful for these types of pickle products. Isolation of appropriate surrogates to assure the safety of heated acid foods has been carried out in parallel with a National Institute of Food Agriculture funded initiative to study continuous flow microwave processing of acid particulate foods. Dielectric properties of acidified vegetables which indicate the ability of materials to store and convert electromagnetic energy into heat were determined at various acid and salt concentrations. The results indicated that salt was the major contributor to changes in dielectric properties of acidified vegetable products and citric acid had minimal effects. These findings provide the information needed in designing a continuous microwave process for pasteurization of acidified vegetables. For sweetpotatoes, a vortex dehydration system was set up and preliminary experiments were performed to examine the effects of sweetpotato chunk size and compressed air temperature on disintegrating and drying the orange-fleshed sweetpotatoes. Progress has also been made in determining the relationship between sugar profiles of sweetpotato genotypes during long-term storage and the quality of fried products. Several sweetpotato clones with low reducing sugars and good fried product quality were identified.
The implementation of a table-salt free fermentation requires the supplementation of the fermentation tanks with a starter bacterial culture. The pickling industry has evaded the use of such starter culture for many years due to the lack of an appropriate culture that could meet Kosher requirements. ARS scientists developed a laboratory scale method for the creation of such culture, which is currently been used by the industry in the table-salt free fermentation trials. The development of a table salt-free fermentation has the potential to revolutionize the pickling industry by reducing the amount of sodium chloride present in the final product so that healthier pickle products are created; and by reducing the chloride concentrations in the waste waters generated from the fermentation process reducing environmental pollution.
Koskiniemi, C.B., Truong, V.D., Simunovic, J., McFeeters, R.F. 2011. Improvement of heating uniformity in packaged acidified vegetables pasteurized with a 915 MHz continuous microwave system. Journal of Food Engineering. 105:149-160.
Perez Diaz, I.M., McFeeters, R.F. 2011. Preparation of a Lactobacillus plantarum starter culture for cucumber fermentations that can meet kosher guidelines. Journal of Food Science. 76(2):M120-M123.
Cervantes-Flores, J.C., Sosinski, B., Pecota, K., Mwanga, R.M., Catignani, G.L., Truong, V., Watkins, R.H., Ulmer, M.R., Yencho, G. 2011. Identification of quantitative trait Loci for dry-matter, starch, and ß-carotene content in Sweetpotato. Molecular Breeding. 28(2):201-216.
Kumar, P., Sandeep, K.P., Alawi, S., Truong, V. 2011. A review of experimental and modeling techniques to determine properties of biopolymer-based nanocomposites. Journal of Food Science. 76(1):E2-E14.
Bridgers, E., Chinn, M.S., Truong, V. 2010. Extraction of anthocyanins from industrial purple-fleshed sweetpotatoes and enzymatic hydrolysis of residues for fermentable sugars. Industrial Crops and Products. 32(3):613-620.
Shi, Q., Vitchuli, N., Nowak, J., Caldwell, J.M., Breidt, F., Bourham, M., Mccord, M., Zhang, X. 2011. One-step synthesis of silver nanoparticle-filled Nylon 6 nanofibers and their antibacterial properties. Journal of Materials Chemistry. 21(28):10330-10335.
Shi, Q., Vitchuli, N., Nowak, J., Caldwell, J.M., Breidt, F., Bourham, M., Zhang, X., Mccord, M. 2011. Durable antibacterial Ag/polyacrylonitrile (Ag/PAN) hybrid nanofibers prepared by atmospheric plasma treatment and electrospinning. European Polymer Journal. 47(7):1402-10409.
Truong, V., Avula, R.Y., Pecota, K., Yencho, C.G. 2011. Sweetpotatoes. In: Sinha, N.K., editor. Handbook of vegetables & vegetable processing. New Jersey: Wiley-Blackwell. p. 717-737.