Inhibition of Listeria Monocytogenes on Cold-Smoked Salmon by Edible Antimicrobial Packaging

Non-Technical Summary:<br/>
Every year within the US, 76 million foodborne illnesses are reported with 325,000 hospitalizations and 5000 deaths. Costs associated with foodborne illnesses are approximately $23 billion every year. Over the past 30 years, listeriosis caused by L. monocytogenes has become a major foodborne disease. There are now over 1500 cases of listeriosis reported every year with 260 fatalities. Pregnant women, infants, and people with compromised immune system are at serious risk. Outbreaks of listeriosis in the early 1980s made the FDA and USDA establish a zero policy on Ready-to-eat (RTE) foods in which the occurrence of L. monocytogenes is considered unacceptable. Seafood has often been associated with foodborne listeriosis outbreaks. Occurrence of L. monocytogenes in RTE seafood ranges from 6% to 36% and can even reach 78%. The FDA/USDA risk assessment included smoked seafood in the list of foods that are at high risk of causing human listeriosis on a per annum basis. Consumer demand for minimally processed seafood has been on the rise. Therefore, there has been a great interest in developing efficient methods to control foodborne pathogens in foods by the use of naturally occurring antimicrobial agents. An alternative approach to control L. monocytogenes is the use of edible films with incorporated antimicrobial systems. Antimicrobial edible films can be used to improve microbiological food safety by reducing the risk of microbiological contamination by prolonged antimicrobial activity on the surface of the food. Edible films are made from various film forming substances that contain protein and carbohydrates. One of the main factors in choosing a raw material for film formation is the cost. The material chosen for packaging should not add much cost to the product. Potato processing waste is an inexpensive and readily available material. Each year approximately 10 billion pounds of potato processing waste is generated within the United States. Essential oils are volatile aromatic liquids obtained from various plant materials. Use of essential oils to preserve foods can ensure food safety by satisfying the consumers demand for minimally processed or natural foods. Essential oils from oregano, bay laurel, Spanish lavender and fennel show antibacterial activity against various foodborne pathogens. Of the essential oils studied, oregano essential oil has shown more antimicrobial activity against L. monocytogenes. The objectives of the study is to develop potato peel waste-based edible films with incorporated oregano essential oil, determine the physical properties of the films, and study their antimicrobial activity against L. monocytogenes inoculated onto the surface of cold-smoked salmon. The films have the potential to inhibit L. monocytogenes on cold-smoked salmon and other RTE seafood and thus ensure the safety of the foods. Demonstration of the effectiveness of the films developed in this study will likely increase the use of potato peel waste.
<P>
Approach:<br/>
Specific Objective 1: Develop edible antimicrobial films from potato peel waste by incorporating oregano essential oil. Edible films will be prepared from potato peel waste (PPW) using a method developed by Kang et al. (2010). Oregano essential oil will be incorporated into films at various concentrations. <br/>Specific Objective 2: Evaluate the physical properties of the films. Film thickness will be measured using Micrometer IP54. Water vapor permeability (WVP) will be measured by Gravimetric Modified Cup method that is based on ASTM standard method E 96-92.Tensile properties will be measured using the ASTM standard method D 882-01 and will include tensile strength (TS), elastic modulus (EM) (Young's modulus) and % elongation at break (%E). Pair wise comparisons equivalent to Fishers LSD will be conducted using Statistical Analysis Software (SAS) version 9.2.
<br/>Specific Objective 3: Evaluate the antimicrobial activity of the films against L. monocytogenes inoculated onto the surface of cold-smoked salmon. Four strains of L. monocytogenes will be used in this study: V7 1/2a, CWD 1157, CWD 1198 and CWD1002. Minimum Inhibitory Concentration (MIC) of oregano essential oil will be determined by an agar well diffusion method modified from that of Winkowski et al. (1992). Antimicrobial activity of potato peel waste films with incorporated oregano essential oil (PPW-OO films) will be evaluated using microbiological growth medium and a method developed by Zivanovic et al. (2004). Vacuum packaged cold-smoked salmon (VP-CSS) with no added preservatives will be challenged with L. monocytogenes V7 1/2a. Growth of L. monocytogenes will be monitored in the presence of PPW-OO films for 28 days at 4oC. Inoculation will be done in two ways: (1) inoculating the surface of salmon with L. monocytogenes and then coating the surface with the PPW-OO film; (2) coating the surface of salmon with PPW-OO film and then inoculating L. monocytogenes on film surface. Inoculated and uncoated salmon as well as un-inoculated and uncoated salmon samples will serve as positive and negative controls. Experimental samples and controls will be vacuum-sealed and stored at 4oC for 28 days. Sampling will be done once a week for 4 weeks. At each sampling time point, samples will be stomached for 2 minutes in 0.1% peptone water and the resulting homogenates will be serially diluted and plated onto TAL plates. The TAL plates are double-layered plates with selective medium on the bottom and non-selective medium on the top (Kang et al., 1999). Oxford Medium will be used as the selective medium in bottom layer while non-selective Tryptic Soy Agar will be used as the top layer when preparing TAL plates. Colonies on TAL plates will be enumerated after incubation for 48 hours at 37oC. For storage studies, pooled ANOVA will be conducted assuming completely random design. Mean comparisons using Pair wise comparison will be conducted using SAS program. Two independent experiments will be conducted with each mean plus (or minus) standard deviation being the average of 4 replicates (two samples from each experiment).
<P>
Progress:<br/>
2012/01 TO 2012/12<br/>
OUTPUTS: Experiments were conducted. The results from the experiments were analyzed. A manuscript entitled "Development of antimicrobial potato peel waste-based edible films with oregano essential oil to inhibit Listeria monocytogenes on cold-smoked salmon was published in Journal of International Food Science and Technology to disseminate the research findings.
<br/>PARTICIPANTS: Nothing significant to report during this reporting period.
<br/>TARGET AUDIENCES: Nothing significant to report during this reporting period.
<br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
<P>
IMPACT: Listeriosis caused by Listeria monocytogenes is a major foodborne illness. Foodborne listeriosis has been linked to the consumption of smoked salmon. Smoked salmon is a ready-to-eat product that is consumed without cooking. However, its pH, salt concentration and aw are within the permissible range for the growth of L. monocytogenes. Edible antimicrobial films allow controlled diffusion of antimicrobials to the surface of food, ensuring controlled release of antimicrobial activity. One of the objectives of our work was to develop edible antimicrobial films using potato peel waste, a new matrix, and oregano essential oil and study their effectiveness against L. monocytogenes on cold-smoked salmon. In our work, potato peel waste-based edible films with oregano oil (PPW-OO) were developed. Incorporation of oil into the films reduced the film strength and increased their water vapor permeability (WVP). The PPW-OO film reduced the growth of L. monocytogenes on cold-smoked salmon during storage under vacuum conditions at 4 degrees Celcius for 28 days. The application of the newly developed PPW-OO films would provide an additional hurdle to the growth of L. monocytogenes on the surface of cold-smoked salmon. The PPW-OO films have the potential to be used as coatings on seafood and possibly other food products to inhibit L. monocytogenes. Demonstration of the effectiveness of the PPW-OO film in this research will likely lead to increase in the use of the potato peel waste, a low-cost or no cost waste-stream.