2012 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.
Scaling up the production of starter cultures that meet Kosher requirements using recycled cover brine solutions and fresh fruits as growth medium was initiated. A collection of potential bacterial cultures for commercial cucumber fermentations and potential probiotic applications was screened to determine the suitability of each bacterium to ferment and produce antimicrobial activities against spoilage microbes. In commercial scale trials on salt-free fermentation, a minimal air purging routine was applied during fermentation and long term storage. Spoilage of the fermented cucumbers without preservatives proceeded between 3 and 6 weeks after primary fermentation indicating that the minimal air purging routine would not be sufficient to prevent the development of spoilage. Therefore, the effectiveness of selected preservatives to prevent spoilage by yeasts and bacteria in commercial-scale salt-free fermentations was evaluated. Successful salt-free cucumber fermentations produced a high quality fermented product that was easier to process due to less shrinking of the fruits and fewer bloaters, and was as equally preferred as the traditionally fermented product by a consumer panel. Semi-commercial scale trials were initiated to further evaluate the ability of fumaric acid and allyl isothiocyante, the spicy component in horseradish and mustard, to preserve acidified cucumbers in reduced salt cover brines. It was observed that fumaric acid was more effective than other traditional preservatives in enhancing the pathogen die-off in refrigerated cucumber products. Fumaric acid can be effectively used to kill Escherichia coli O157:H7 without significantly affecting the acceptance of the product, as determined by sensory analysis. Combinations of lauric arginate with natural preservatives for maintaining microbial stabilization and environmentally friendly preservation of cucumbers without fermentation are currently being evaluated. In response to emerging needs of the stakeholders, studies were initiated on natural color alternatives, such as turmeric, which resulted in better-liking by a consumer panel in replacing FD&C yellow #5 in the current pickle formulations. In addition, a repeated "hot brine" filling method for pasteurization of pickle spears was evaluated to replace tunnel pasteurizers, which may result in reduced energy and equipment costs for the acidified vegetable industry. For sweetpotatoes, a vortex dehydration system operated with compressed air at 150 psi and 110-125°C was effective in disintegrating and instantly dehydrating sweetpotato chunks into fine flours. Progress has been made in identifying potential sweetpotato clones from the breeding programs for fried product quality as affected by sugar profiles. Effects of post-harvest handling practices on storability and processing performance of commercial sweetpotato cultivars were also evaluated. Cured sweetpotatoes stored at 13-15°C for up to 11 months had no adverse effects on sensory and physicochemical properties of the coated French fries demonstrating that acceptable product quality with low fat content (<10%) and high carotene (10mg/100g) can be produced year round.
Microbiology of low-salt vegetable fermentation spoilage. Disposal of high salt waste from fermentation of vegetables is an ongoing problem for the pickle industry. The ability to store cucumbers in bulk with less salt is difficult because of the increased susceptibility to microbial spoilage. Scientists at the USDA-ARS Food Science Research Unit in Raleigh, NC have identified microorganisms responsible for this post-fermentation spoilage and the resulting chemical changes that occur in a wide range of salting conditions. Yeasts, Pichia manschurica and Issatenchia occidentalis and lactic acid bacteria, Lactobacillus buchneri and Lactobacillus parafarraginis had the ability to initiate spoilage by degrading the lactic acid that was produced naturally during fermentation, resulting in a rise in pH. Spoilage of fermented cucumbers was successfully recreated in the laboratory with isolated organisms and the natural cucumber microflora. The potential role of each microbe isolated from commercial fermented cucumber spoilage was evaluated in pure and mixed cultures, and it was learned that the co-existence of selected microbes in a cucumber fermentation model system enhances their ability to cause spoilage. Knowledge of the organisms and biochemical pathways involved opens the door for development of preventative measures that will allow fermentation to be achieved with less salt.
Allen, J.C., Corbitt, A.D., Maloney, K.P., Butt, M.S., Truong, V.D. 2012. Glycemic index of sweetpotato as affected by cooking methods. Open Nutrition Journal. 6:1-11.
Franco, W., Perez-Diaz, I.M., Johanningsmeier, S.D., McFeeters, R.F. 2012. Characteristics of spoilage-associated secondary cucumber fermentation. Applied and Environmental Microbiology. 78(4):1273-1284.
Leksrisompong, P.P., Whitson, M.E., Truong, V.D., Drake, M.A. 2012. Sensory attributes and consumer acceptance of sweetpotato cultivars with varying flesh colors. Journal of Sensory Studies. 27:59-69.
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Johanningsmeier, S.D., Franco, W., Perez Diaz, I.M., McFeeters, R.F. 2012. Influence of sodium chloride, pH, and lactic acid bacteria on anaerobic lactic acid utilization during fermented cucumber spoilage. Journal of Food Science. 77(7):M397-M404.
Truong, V.D., Hu, Z., Thompson, R.L., Yencho, G., Pecota, K.V. 2012. Pressurized liquid extraction and quantification of anthocyanins in purple-fleshed sweetpotato genotypes. Journal of Food Composition and Analysis. 26:96-103.