Type of Document Thesis Author Alderees, Fahad Author's Email Address firstname.lastname@example.org URN etd-10072010-204910 Title Assessing the Shelf Life of Retail Shrimp Using Real-time Microrespirometer Degree Master of Science Department Nutrition, Food, and Exercise Science, Department of Advisory Committee
Advisor Name Title Yun-Hwa Peggy Hsieh Committee Chair Bahram H. Arjmandi Committee Member Fred W. Huffer Committee Member Keywords
- Shelf Life
- Carbon Dioxide
- Respiration Rate
Date of Defense 2010-09-09 Availability unrestricted AbstractShrimp is the most consumed seafood item in the United States (U.S.). Currently 90% of the shrimp consumed in the U.S. is imported from a few Asian countries. When imported shrimp arrives to its destination, it probably contains a load of microbial contamination due to the post-harvest processing steps such as transportation, handling, preparation, beheading, peeling, deveining, packaging and storage that could add further bacterial contamination. Most of the U.S. import refusals belong to seafood shipments due to the detection of bacterial contamination and filthy appearance.
Upon shipment arrival, testing for microbial activities of seafood requires a two day incubation period when using the traditional Aerobic Plate Count (APC) method; however, a novel non-instrumental microrespirometer which was developed by Hsieh and Hsieh (2000) can determine the microbial activity of the sample in real-time by measuring the CO2 evolution rate (CER). CO2 is a byproduct of microbial respiration which can be used as a direct indicator of biological activity. The unique characteristic of this method is that it is a simple device that can determine the microbial activity in food less than one hour and is highly sensitive in determining the CER and simple to operate. The use of the microrespirometer instead of the APC in testing the imported seafood shipments will save a great deal of time and lower the cost for both importers and exporters by lowering the testing cost and reducing the costly waiting time at the ports.
The specific objectives of this study are: 1) to validate the real-time microrespirometer method by correlating the rapid CER results with the traditional cultural APC method, 2) to establish a shrimp spoilage cut-off value of CER using the microrespirometer method by comparing the results with sensory analysis, 3) to exam the effect of chloramphenicol on shrimp shelf life using non-instrumental microrespirometer, APC method and sensory analysis and 4) to compare the shelf life of farm-raised imported shrimp with domestic wild-caught shrimp using non-instrumental microrespirometer, APC, pH and sensory analysis.
Frozen domestic wild-caught shrimp (Penaeus duorarum) and imported farm-raised shrimp (Panaeus vannamei) were purchased locally. Domestic shrimp were treated with chloramohenicol at 10 and 30 ppm and stored at 4°C along with the untreated domestic and imported shrimp. Samples were tested daily using the microrespirometer, APC, pH and olfactory sensory analysis. The p values and correlations between CER, APC and sensory analysis were determined using SPSS Statistic software and Microsoft Excel 2007. The microrespirometer and pH determinations were done in triplicate; the APC was performed in duplicate and the experiments were repeated twice.
The CER method was found to be highly correlated with the APC (R˛=0.812 to 0.929) for all samples stored at 4°C. When samples’ spoilage odor became noticeable, the average CER value of all samples was 27.23 µl/h/g. In order to allow for a small safe margin, a CER value of 25 µl/h/g was identified as a safe cut-off value for raw shrimp stored at 4°C. Samples treated with chloramphenicol had significant (P <0.05) lower APC and CER values compared to untreated samples; also, their sensory analysis was rated lower (3.14) than the untreated samples (4.80) at the endpoint of spoilage. This is an indication that the drug treatment had lowered the initial load of specific spoilage organisms at the start of storage causing an increase in the shelf life. Chloramphenicol treatment increased samples’ shelf life by three days compared to the untreated samples. Retail imported shrimp had a higher bacterial load and shorter shelf life by one day than the domestic shrimp. The pH measurements did not differ much throughout the study and it cannot be used as a reliable method to determine shrimp quality.
The difference in microbial quality and shelf life of various (source of origin and drug treatment) shrimp samples were able to be determined rapidly and accurately when using the real-time CER method.
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