Location: Warmwater Aquaculture Research Unit
2012 Annual Report
Objectives
Research will address methods to determine the presence of pathogens in catfish/catfish products and to maximize elimination methods. Detection techniques will be developed to aid in processing and packaging operations, which should further enhance product safety. Specifically the new objectives are: 1)Optimize safety of aquaculture products through innovative processes for reducing microbiological, physical and chemical hazards in seafood/aquaculture products. 2)Determine the mechanisms influencing microbial survival of selected pathogens in seafood/aquaculture products. 3)Optimize the market value of seafood/aquaculture products through enhanced food safety and quality.
Approach
Catfish. Determine optimum rates of microbial reduction through innovative processing in catfish products including evaluation of consumer acceptance. Determine viable methods of hazard reduction (smoking, acidulants, antimicrobials, etc) in catfish products during processing and storage. Determine the methods by which these methods reduce hazards within the products evaluated. Enhance the physical safety of catfish fillets with innovative analysis technology.
Seafood/Produce. Determine the efficacy of IQF freezing, irradiation, and high pressure processing and other technologies on the safety and quality of oysters, shrimp and produce.
Objective 2: Catfish/ Seafood/Produce. Determine the mechanistic approach by which the certain pathogenic bacteria may be reduced in aquatic species. Utilize PCR analysis and other assays to determine the sensitivity and specificity of various isolates in response to innovative treatments.
Objective 3: Catfish. Enhance product value through innovative smoking and further processing of catfish fillets. Value-added analysis will compared products to commodity value for product enhancement addition. Evaluate value-added products to address potential food safety issues.
Seafood/Produce. Evaluate consumer acceptance of products enhanced through various processing methods. Preparation techniques, ingredient inclusion, packaging and storage methods will be evaluated at various time frames and inclusion rates to determine specie specific parameters limitations. Analyze economics of various market potentials.
Catfish. Determine optimum rates of microbial reduction through innovative processing in catfish products including evaluation of consumer acceptance. Determine viable methods of hazard reduction (smoking, acidulants, antimicrobials, etc) in catfish products during processing and storage. Determine the methods by which these methods reduce hazards within the products evaluated. Enhance the physical safety of catfish fillets with innovative analysis technology.
Seafood/Produce. Determine the efficacy of IQF freezing, irradiation, and high pressure processing and other technologies on the safety and quality of oysters, shrimp and produce.
Objective 2: Catfish/ Seafood/Produce. Determine the mechanistic approach by which the certain pathogenic bacteria may be reduced in aquatic species. Utilize PCR analysis and other assays to determine the sensitivity and specificity of various isolates in response to innovative treatments.
Objective 3: Catfish. Enhance product value through innovative smoking and further processing of catfish fillets. Value-added analysis will compared products to commodity value for product enhancement addition. Evaluate value-added products to address potential food safety issues.
Seafood/Produce. Evaluate consumer acceptance of products enhanced through various processing methods. Preparation techniques, ingredient inclusion, packaging and storage methods will be evaluated at various time frames and inclusion rates to determine specie specific parameters limitations. Analyze economics of various market potentials.
Progress Report
Research related to quantification, identification and control of pathogens in food products, in particular Listeria (L.) monocytogenes, is focused on developing strategies for understanding virulence factors and reducing L. monocytogenes in catfish, seafood, and other meat products. Virulent factors for L. monocytogenes have been identified as well as proteins responsible for attachment strength on reay-to-eat (RTE) foods. This information will be critical in developing tests and protocols required to control L. monocytogenes in catfish, seafood, and other RTE products. Rapid and sensitive tests for detection of Salmonella and Escherichia (E) coli 0157:H7, and were developed, whereas tests for detection of Vibrio vulnificus and Listeria, and botulism neurotoxin are being developed and validated. These assays assay will be useful for screening live/on farm and final products. Understanding of catfish fillet redness is being studied with the vision of helping develop industry guidelines to enhance filet color uniformity or predict filet color. Antimicrobials in the form of bacteriophages or naturally-derived were tested against pathogens in vitro and in seafood matrices with good results. Minimum inhibitory concentrations were found for each of the compounds or for those used in a mix. Ready-to-eat catfish products were developed. These could increase the offer of value-added catfish products in the market, expanding the industry competitiveness edge. These research projects will play a role in assuring safe, high-quality food products to consumers and will be important to maintaining viable aquaculture and seafood industries in the U.S.
Accomplishments
1. Determination of the genome sequence of a virulent serotype of Listeria monocytogenes. Listeria monocytogenes is a human pathogen but some strains and other species could be non-virulent. This work determined the genomic sequence and identified 58 virulence-specific genes for a virulent strain of Listeria monocytogenes. This can potentially allow development of methods to distinguish pathogenic and nonpathogenic isolates. Polymerase chain reaction (PCR) assays based on eight of these virulence-specific genes were tested on a panel of listerial isolates, and two of the genes showed good potential. The goal is development of a multiplex real-time PCR assay for simultaneous and rapid differentiation and quantification of high-risk and low-risk L. monocytogenes serovars from food, particularly aquaculture products. This assay will allow us to address important questions regarding persistence and replication of different listerial serotypes in food and in processing environments.
2. Novel genetic differences between pathogenic and nonpathogenic isolates. Discrimination between pathogenic and non-pathogenic Listeria (L.) monocytogenes with accurate diagnostic tools can help the industry (food and fish) better discern the safety of their products. A large number of food recalls occurs annually because of the possibility of being contaminated with L. monocytogenes, even though the strain may not be virulent. The identification of novel targets that could differentiate pathogenic and nonpathogenic isolates has taken on increased importance. Results show that one could discern between pathogenic and non-pathogenic strains by determing the presence or absence of certain genes. This could lead to the development of tools to identify whether a product or animal carries a pathogenic strain or whether it is safe to eat even though it may carry Listeria monocytogenes.
3. Natural antimicrobials that can inhibit Vibrio (V.) vulnificus and V. parahaemolyticus in shucked oysters. Vibrio in oysters account for many foodborne outbreaks, are responsible for economic and social hardship to fishermen and others, and also responsible for increased health care costs. This work looked at some natural antimicrobials that could be utilized to inhibit Vibrio spp. growth and thus prevent foodborne illnesses. It was found that citric acid, grape seed extract and lactic acid solutions at fairly high concentrations could be used to suppress growth of these pathogens. These findings can serve to develop formulations to add to oysters to minimize foodborne illnesses when consumed.
4. Attachment of Listeria monocytogenes on the surface of ready-to-eat (RTE) products. Understanding the mechanisms of attachment may help to elucidate the persistence of Listeria monocytogenes in ready-to-eat products and thus find ways to inhibit it by detaching it from the food or not allowing attaching to the food. A gene was identified as responsible for attachment (at least in part) of Listeria monocytogenes in RTE foods like fresh fruits and vegetables. The binding was found to occur with cellulosic material in the fresh produce. This hypothesis was tested and validated. Thus, a system to prevent attachment to cellulosic material or to detach the organism can be designed. This can enhance the safety of fresh and fresh-cut fruits and vegetables, a category of foods responsible for a large number of foodborne outbreaks annually.
5. Enhanced functional properties of tannic acid after thermal hydrolysis. Tannic acid has been proven to possess antioxidant and antimicrobial properties thus being a powerful bioactive component. However, there could be potential for enhancing its functional properties by manipulation of the compound per se or in food or other matrices. Thermal hydrolysis at high pressures of fresh tannic acid resulted in shorter chain but more powerful components produced: gallic acid and pyrogallol. This process could be utilized to enhance natural antimicrobial properties of tannic-acid containing foods or to enhance functional properties of tannic acid to be used as additives in food and feed.
6. Detection of Botulinum toxin contamination of catfish. Clostridium Botulinum Type E is associated with seafood including aquaculture products. It has been discovered that this organism is beginning to affect fish at the farm level since it produces a powerful toxin, Neurotoxin E. It is very difficult to separate the toxin from a complex matrix like fish. Preliminary results have shown progress in eliminating enzymes responsible for eliminating the toxin and thus make the detection method more sensitive and accurate. The development of this procedure will aid the catfish and other aquaculture/seafood industries tremendously as a diagnostics tool to react and treat prior to total loss.
7. Potassium acetate and lactate enhance quality of marinated catfish fillets. Shelf-life of fresh/iced catfish fillets and other fresh products is a problem in the industry. Development of systems that can extend shelf-life while adding value to these products can be beneficial to the industry. The treated fillets had a longer self-life and were preferred by consumers (when fried) over untreated fillets. Thus, incorporation of these organic salts in catfish products not only enhances their quality but also provides for longer shelf-life and thus fewer losses.
8. A quick and easy test for identification of human pathogens in seafood and other products and the environment. Testing at the processing level for the presence of pathogens in the food is very tedious, time consuming and requires lots of training for the most part. Novel testing kits utilizing two-phase media with a mix of indicators, growth promoters and/or inhibitors have been developed or are being developed. These kits will allow processors and handlers of food to screen their production lots and their environments in relatively short times for the presence of pathogens and thus clear product for market in a rapid and reliable manner.
9. Prevention of food safety and food quality problems associated with larval nematodes in commercial catfish. The most prevalent population of turtles in commercial catfish ponds are the red-eared sliders and that they are frequently heavily infected with two nematodes, Serpinema sp. and Camallanus sp. which can also infect fish. Both Serpinema and Camallanus have been sequenced and work is underway to develop molecular probes to screen for their presence. This work will provide for a rapid screening tool for these nematodes and thus reduce fish losses at the farm.
Review Publications
Bradley, E.M., Williams, B., Schilling, W., Coggins, P., Crist, C., Yoder, S.W. 2011. Effects of sodium lactate and acetic acid derivatives on the quality and sensory characteristics of hot-boned pork sausage patties. Meat Science. 88:145-150.
Soni, K., Nannapaneni, R. 2010. Bacteriophage significantly reduces Listeria monocytogenes on raw salmon fillet tissue. Journal of Food Protection. 73:32-38.
Donaldson, J.B., Nanduri, B., Pittman, J., Givaruangsawar, S., Burgess, S.C., Lawrence, M.L. 2011. Proteomic expression profiles of virulent and avirulent strains of Listeria monocytogenes isolated from macrophages. Journal of Proteomics. 74(10):1906-1917.
Steel, C.L., Donaldson, J.R., Paul, D., Barnes, M.M., Burgess, S.C., Arick, T., Bridges, S.M., Lawrence, M.L. 2011. Genome sequesnce of lineage III Listeria monocytogenes strain HCC23. Journal of Bacteriology. 193:3679-3680.
Kim, T., Silva, J.L., Jung, Y. 2010. Enhanced functional properties of tannic acid after thermal hydrolysis. Food Chemistry. 126:116-120.
Soni, K., Nannapaneni, R., Tasara, T. 2011. The contribution of transcriptomic and proteomic analysis in elucidating stress adaptation responses of Listeria monocytogenes. Foodborne Pathogens and Disease. 8:842-852.
Soni, K., Nannapaneni, R., Tasara, T. 2011. An overview of stress response proteomes in Listeria monocytogenes. Agriculture, Food and Analytical Bacteriology. 1:66-85.
Kin, S., Schilling, W., Smith, B.S., Silva, J., Kim, T., Pham, A. 2011. Potassium acetate and potassium lactate enhance the microbiological and physical properties of marinated catfish fillets. Journal of Food Science. 76(4):5242-5250.
Soni, K., Nannapaneni, R., Hagens, S. 2010. Reduction of Listeria monocytogenes on the surface of fresh channel catfish fillets by bacteriophage listex P100. Foodborne Pathogens and Disease. 7:427-434.
