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Department of Food & Nutritional Sciences

Food Safety Research

Graduate Thesis Abstracts

Characterize and Antimicrobial Activity of Sweetpotato Starch-Based Edible Film Containing Origanium (Thymus Capitatus) Oil

By Fabienne E. Ehivet, 2010, Major Professor: J Oh
Edible packaging had been used to extend shelf life and preserve the freshness of food products since the twelfth century. However, the current increase in consumer demand for environmentally friendly packaging has renewed interest in edible food packaging. Likewise, seemingly intractable issues caused by foodborne pathogenic bacteria have led to the development of the revolutionary antimicrobial active packaging which is able to reduce microbial growth on food. The main objectives for the study were (1) to characterize the mechanical (tensile strength and elongation) and barrier (water vapor permeability) properties of a sweetpotato starch-based edible film, and (2) to test and analyze the effectiveness of the antimicrobial activity of the sweetpotato starch-based edible film containing origanum (thymus capitatus) oil (OG) against three common food-borne pathogenic bacteria.Sweetpotato starch was extracted from locally available sweetpotato roots following the procedure developed by Wischmann et al. (2006) with minor modifications. A sweetpotato starch-based film (SPSF) was fabricated using a casting method on a Teflon taped plate (25 x 25 cm). The films were fabricated with selected concentrations of starch (1.0, 2.0, 2.5, 3.0, 4.0, and 50%) and plasticizers (glycerol, sorbitol, sucrose, proplene glycol) at concentrations of 20, 30, 40, and 50% were evaluated for mechanical and barrier properties. SPSF containing OG (0.5, 1.0, 1.5, and 2.0%) were also fabricated to determine the antimicrobial activities against E. coli 0157:H7, Salmonella enteritidis, and Listeria monocytogenes using the standard agar diffusion assay.  The film containing 2.5% sweetpotato starch exhibited the greatest tensile strength (4.58 MPa) among the tested films (P<0.05). Sorbital at the concentration of 40% was determined as the optimum plasticizer based on the mechanical properties (TS of 7.69 and E of 77.92%) and water vapor permeability (0.212 ng m/m2S Pa). The antimicrobial activity of the film containing OG, determined by square of zone width, increased as the concentration of OG increased . The SPSFs containing OG exhibited inhibitory effects against S. enteritidis and E. coli 0157:H7 than L. monocytogenes (P < 0.05). This research suggests that sweetpotato starch-based edible film containing OG can be utilized to enhance the safety the safety of food by inhibiting foodborne pathogenic bacteria.

Application of Edible Packaging with Chitosan Polymer to Commercial Cheese Products

By Nagat Y Ibrahim, 2006, Major Professor: J Oh
Edible packaging with chitosan polymer coating and film were applied to organic cheese products stored for 8 days at 30°C.  The preservative effect of this edible packaging was assessed by color measurement, pH, relative moisture content (RMC), texture, and microbiological assays using Gram-negative bacterium, Echerichia coli K12. The efficacy of chitosan coating and film were compared to two controls, cheese without any packaging and wrapped with plastic film. At the end of storage period, chitosan coating did not affect lightness, but did result in an increase in redness of cheese. Cheese wrapped with chitosan film had lower L* values, and higher a* values (p<0.05), indicating that these cheeses became darker over the storage time. Cheese coated and wrapped with chitosan had similar yellowness. Cheese coated with chitosan had significantly lower pH values compared to cheese wrapped in chitosan film (p<0.05). The cheese exhibited similar RMCs and hardness regardless or chitosan packaging used. Cheese wrapped with plastic film had marginal changes in color, the lowest pH, and the highest RMC. Cheeses wrapped with plastic film were significantly softer than other treatment (p<0.05).  The pour plate method and serial dilution were conducted to count microbial colonies. Both chitosan coating and film inhibited the growth of E.coli  K12 on the cheese because of the antimicrobial activity of chitosan polymer. Chitosan coating and film exhibited similar inhibitory activities.  The bacterial growth was inhibited approximately by 2-log with chitosan coating and approximately 1.5-log reduction with chitosan film.  Cheese wrapped in plastic film exhibited the highest number of colony forming units per mL (CFU/mL) (p<0.05).  The control without any treatment also showed log reduction; however; the reduction was caused by the dryness of the cheese during storage.  Overall, the results suggest that the edible packaging with chitosan polymers with either coating or film would enhance the quality of cheese and increase its safety during storage, transportation and handling.  The chitosan coating exhibited better preservation effects than the chitosan film in terms of microbial safety and quality factors such as lightness, redness and pH retention.
Key words: Chitosan, edible film, antimicrobial activity, cheese quality. 

Influence of Harvest Time on Growth Responses and Omega-3 (Ω-3) Fatty Acid Content of Purslane (Portulaca oleraceae) 

By Damicca S. Johnson, 2005, Major Professors: D Mortley and J Oh
Over the last decade, focus on purslane (Portulaca oleraceae) has shifted from its labeling as a recalcitrant weed to the discovery that it contains the highest concentration of omega-3 (ω-3) fatty acid among several green leafy plant species including, spinach, red leaf lettuce, buttercrunch lettuce and mustard greens. The health benefits of ω-3 fatty acids in the diet are well established, ranging from the lowering of triaylglycerols in the blood to the reduction in risk of certain types of cancers. While there are other sources of omega-3 fatty acids, they are usually more expensive than purslane. The objective of this study was to evaluate the influence of harvest times on growth responses and the omega fatty acid content of purslane. Purslane plants were grown in a greenhouse and harvested sequentially at 20,40 or 60 days after transplanting (DAT), corresponding to 42, 63 and 84 days after sowing. Results showed that harvest intervals significant influenced foliage fresh and dry weights, leaf number, plant height, root length and weight. There was a significant interaction between harvest intervals and replication (P≤0.05) for root weight. Harvest intervals significantly (P≤0.01) influenced foliage fresh and dry weight, leaf number, plant height, root length and root weight. Interactions between harvest intervals and replications were significant (P≤0.01) for foliage dry weight, root length and root weight.Fatty acid analysis by Gas Chromatography Mass Spectroscopy (GCMS) verified the presence of myristate, palmitate, linoleate and linolenate in all three harvests, while stearate and oleate were detected only in the last two harvests (40 and 60 DAT). Myristate, palmitate, linoleate and linoleate increased significantly from harvests one to two. For harvest one, purslane contained the following fatty acids in mg/kg: myristate 68.2, palmitate 49.0, linoleate 34.8 and linolenate 78.9. for harvest two, purslane contained (mg/kg), myristate 236.8, palmitate 166.0, stearate 90.4, oleate 103.9, linoleate 173.9 and linoleate 161.3. The third harvest contained (mg/kg) myristate 240.5, palmitate 330.3, stearate 273.3, oleate 253.9, linoleate 336.8 and linolenate 305.3. The ω-6/ω-3 fatty acid ratios found in purslane were 0.44, 1.08 and 1.10, respectively, for harvests 1 through 3. Ratios for harvests two and three were equal to, or greater than those necessary for human dietary needs (1:1 to 1:7). These results suggest that the optimal harvest time to achieve an ideal ratio of ω-6/ω-3 fatty acids and dry matter production and reap the full benefits of a rapid cycling and highly nutritious fresh vegetable for consumption probably ranges between 40 and 60 DAT.

Control of E. Coli O157:H7, Shigella Sonnei and Salmonella Typhimurium in Model Foods with Phage ETU3-An Investigation

By Blair S. DeJan, 2002, Major Professor: A Dessai
The emergence and reemergence of virulent forms of foodborne pathogens such as Escherichia coli O157:H7, Shigella and Salmonella have increased the requirement for effective technologies to maintain and enhance the safety of our food supply. Bacteriaphage is a natural antimicrobial agent that has potential for the possible food application to inhibit the growth of pathogens like Escherichia coli O157:H7, Shigella and Salmonella. In this study, the ability of bacteriophage ETU3 to control Escherichia coli O157:H7, Shigella and Salmonella were investigated in two food systems, namely Ground Beef Slurry (GBS) and milk. Each test pathogen was inoculated in GBS or milk and challenged by phage ETU3 inculcation at 20°C. For quatitative analysis, samples were drawn at 0, 8, 24, 32, 40 hours or 0, 24, 48, and 72 hours for milk or GBS models, respectively.Phage ETU3 was effective in inhibiting growth of all the three test pathogens in both the food systems. Bacteriophage ETU3 at 20°C showed a 4.89 log10CFU reductions in E. coli 0157:H7 population in GBS, while in Pamalat milk population, reduction was 3.41 log10CFU. With Shigella somei there was a 4.40 log10CFU reduction in GBS and a 3.413 log10CFU reduction in Pamalat milk. Phage ETU3 showed only a 2.45 log10CFU reduction in Salmonella inoculated in GBS while in Pamalat milk ETU3 resulted in a 3.413 log10CFU reduction in Salmonella. Phage ETU3 seems to be effective in both the food systems tested and may need further research to enhance its effectiveness in test food systems.  

Department of Food and Nutritional Sciences, 204 Campbell Hall, Tuskegee University, Tuskegee, AL 36088
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