John T. Lindsay, Ph. D., Peter F. Schoch,
Jim Conley, and Jarvis Franzblau
Escherichia coli O157:H7 has been linked to major food borne disease outbreaks through many sources including meat, dairy products, hamburger meat, apple juice and water in the USA and vegetables in Japan.1 The United States Department of Agriculture’s (USDA) Economic Research Service estimates that diseases caused by E.coli O157:H7 due to consumption of insufficiently cooked ground beef result in $200 – $400 million in annual medical costs and productivity losses.2
In the U. S. irradiated ground beef was introduced into commercial channels in early 2000 following approval by the FDA in 1997 and the USDA Food Safety Inspection Service in 1999. The number of supermarkets carrying this product has increased from 84 in May 2000 to over 7,000 in March 2003.3 Several major meat processing companies have incorporated irradiation into their processing procedures to ensure the micro-biological safety of their products. Fast food restaurants and other chain restaurants are beginning to offer irradiated meat on their menus.
The United States Depart of Agriculture (USDA) estimates that the American consumer will receive approximately $2 in benefits such as reduced spoilage and less illness for each $1 spent on food irradiation. In 2000, electron beam and X-ray machines were introduced into the American food processing system. Previously, only cobalt-60 irradiators had been used for food irradiation. When electron beam or X-ray machines are used, no radioactive isotopes are involved and the radiation can be turned off at will.
Lexatronics, LLC is a Michigan based company that has a patent pending for the use of low energy x-rays for the irradiation of foodstuffs. In this case, low energy is defined as an x-ray energy spectrum for which the maximum energy is 250 kVp or less. The actual maximum energy used is dependent upon the product being irradiated, the geometry used, and the level of penetration that is necessary.
Our specialized process allows a food processor to install one of our machines in their own plant and irradiate foodstuffs in-line with their other processes. For example, our machines could be placed in the current product line as the last step prior to packaging. Our approach provides for the custom design of the machine for very specific products and product shapes. We have a second prototype machine (Rainbow II) built and currently in use in Wixom, Michigan. Rayfresh Foods, Inc. holds the exclusive rights to market the Rainbow Process.
This process can be used to treat a variety of foods ranging from red meats and poultry to fruits, vegetables and eggs, to fruit juices or any of the other approved items to destroy food borne pathogens and extend shelf life. Our process would also be ideal for treating ready-to-eat items such as lunchmeats or deli foods to eliminate Listeria.
We have used our process to successfully irradiate:
1. Several juices including: orange juice, apple juice, apple cider, grape juice, and grapefruit juice;
2. Several meat products including: ground beef, ground sausage, whole sausages, ready to eat meats, and hotdogs;
3. Several chopped vegetables including: white onions, green onions, lettuce, celery, green peppers, and mushrooms;
4. Several whole vegetables including: onions, mushrooms, cherry tomatoes, and nuts (almonds); and
5. Several fruits including: cherries, blue berries, chopped cantaloupe, green grapes, and raspberries.
In all cases we were able to irradiate the product without adverse effects to the product and increased shelf life significantly over non-irradiated product.
We have been able to
1. Reduce and/or eliminate Pathogens such as E-coli.
2. Extend shelf life on Fresh Squeezed Orange Juice from 5 days to over 30 days,
3. Extend shelf life on Fruits and Vegetables,
4. Stop Fermentation in items such as Apple Cider,
5. Kill Molds and Yeasts on Fruits and Vegetables, and
6. Treat contaminated foods so they are safe for consumption.
In conjunction with the Michigan State University we have used the Rainbow Process to eradicate E-coli O157:H7 in ground beef. Ground beef was inoculated with E-coli O157:H7 and divided into 25 gram sample sizes. Figure 1 shows the samples and the Pb box used to irradiate the samples. Figure 2 shows how the samples were placed in the irradiator.
Figure 1. Samples packaged in 25 gram allotments, placed in plastic bag, and then into the irradiation holder.
Figure 2. Irradiation holder (Pb box) placed in irradiator.
The objective of this study was to monitor the survival of E. coli O157:H7 in ground beef treated by irradiation. A three strain-cocktail of E. coli O157:H7 was inoculated into ground beef provided by Rayfresh Foods, Inc. at 1.62 x 106 CFU/g. Twenty five grams of inoculated ground beef was weighed and placed in sterile plastic bags. Fourteen bags with inoculated beef (12 for irradiation treatment and 2 for controls as inoculated but not irradiated) were transported to Rayfresh Foods, Inc. for irradiation treatment. One bag of beef without inoculation served as a background control and was processed immediately in the lab at Michigan State University (MSU). After irradiation was conducted at Rayfresh Foods, Inc., the bags were transported back to MSU for detection of E. coli O157:H7. Twenty five grams of ground beef in each bag was diluted with 100 ml Phosphate Buffer Solution (PBS. PH 7.4), processed in Stomacher for 2 min., spiral plated onto MacConkey agar with sorbitol (SMAC) and incubated at 27 C for 24 hours. The results are shown in Figure 3.
Figure 3. E-coli O157:H7 as a function of time with distance between X-ray source and sample position equal to 2.5 inches.
The above series of experiments was repeated using a greater distance from x-ray generator and sample position for two different energies, E1 and E2, E1 > E2. Figure 4 shows the results from this experiment.
Figure 4. E-coli O157:H7 (CFU/g) as a function of time and energy with the distance between X-ray source and sample position equal to 5.5 inches.
The above results clearly show that the Rainbow ProcessTM can be used to eradicate E.-coli O157:H7. The Rainbow ProcessTM has the added advantages of being safe (it can be turned of at the end of the day and takes millimeters of shielding, not feet), it can be placed directly into the producers line with minimal alterations, it is economical, it is portable, and infinitely versatile.
* Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824
1. Facts about food irradiation, A series of Fact Sheets from the International Consultative Group on Food Irradiation (ICGFI),(1999)http://www.iaea.org/icgfi/.
2. FDA(1997) Irradiation in the Production, Processing and Handling of Food, Depart of Health and Human Services, United States Food and Drug Administration, December 3, 1997, Volume 62, Number 232, Pages 64107-64121.
3. Paisan Loaharanu, M.S., Irradiated Foods, Fifth Edition,, Publ. American Council on Science and Health, New York, NY 10023-5860 (May 2003).
1.What is Food Irradiation
2. Why irradiate foods?
3. What types of radiation
4. What can irradiation do?
Click here for more FAQ
Michigan State University Biosystems Collaboration Letter
Rayfresh Foods has developed an economical way to irradiate food products within the scheme of a continuous process. This in-line system helps in the quest for food safety. Our by-products are safe, healthy foods, and extended shelf life with no discernable change in taste and texture. By passing light through a product using x-rays, we can only add to a processors already clean and safe practices. Although no one thing can eliminate all the risks associated with food processing, Rayfresh Foods Rainbow Process will move us closer to safe tables.