Q: Dr. Brendan Niemira [Acting Research Leader, Microbial Food Safety Research Unit, USDA-ARS Eastern Regional Research Center, Wyndmoor, Pennsylvania] recommended I speak with you. He was involved with the USDA report presented in April at the American Chemical Society regarding irradiation of fruits and vegetables. [You can read his reports here and here.] He says you have done excellent work in the area of tomatoes. Could you share your findings?
A: We have worked on irradiation of diced tomatoes. We have not done whole tomatoes. The gamma radiation facility in Florida has done whole tomatoes quite successfully. However, they haven’t inoculated them with Salmonella as we have done with diced tomatoes. Our testing has included five strains, but not Saintpaul.
Q: Are all strains of Salmonella similar in how they react to irradiation treatments?
A: Every strain behaves just a bit different. That’s true for any technology. Some are more resistant than others. You really want to make sure the most resistant one is being restrained by an adequate amount.
Q: What did you learn through your research and testing?
A: Generally, Salmonella is somewhat resistant to irradiation compared to E. coli. To kill Salmonella you need to irradiate 1.4 to 1.9 killogray. With E. coli, you could get a 5 log reduction at 1 killogray. Salmonella is 1.5 times to 2 times as resistant to irradiation.
Q: Does irradiating at that level change the product in any way?
A: When you irradiate diced tomatoes at dose sufficient to kill 5 logs of Salmonella, and that should be plenty, you do see a little softening of diced tomatoes. If presented to consumers, diced tomatoes irradiated at 2 kilogray would be soft.
Q: Is there a solution to counter that problem?
A: What we actually did, we dipped the diced tomatoes in calcium chloride. Calcium chloride is used in diced vegetables to maintain firmness. Once dipped, we were able to maintain firmness; we irradiated them and destroyed the Salmonella.
Q: Does this process change the taste, texture or flavor profile?
A: It doesn’t really change the taste. We did sensory work and it was received quite well.
Q: That doesn’t sound like a ringing endorsement…
A: Let’s just say I wouldn’t present irradiated tomatoes at the best restaurants. You can tell a difference. You can tell one has been dipped in calcium chloride. It does give it a little bit of a chalky taste. The next part of the study would be to do tweaking to optimize the treatment. We need to adjust it to minimize the negative and maximize the sensory benefits. We’re not quite there yet.
Q: For industry executives who are interested in delving deeper, is there a way for them to get a copy of your report?
A: We did this study over the past couple of years. It was published this year. Here’s the abstract.
Q: What is your perspective on the Tomato/Salmonella Saintpaul outbreak?
A: The FDA seems to be having trouble finding where it’s coming from.
Q: If the tomato industry implemented an irradiation program, could outbreaks such as these be eliminated?
A: My key message is irradiation is one tool we can use among many others. It doesn’t take the place of good agricultural practices in the field or during the manufacturing process. If someone in the field thinks they can use sloppy methods, they should think again.
The most feasible scenario is that the tomatoes were contaminated with irrigation water. If that does happen, adequate washing is helpful, but it may not completely remove Salmonella. Critics of irradiation are concerned it will lead to sloppy practices. If you start with bad product, irradiation won’t fix it.
Q: Many consumers also have negative associations with irradiation. Could those be difficult to overcome?
A: People have been skeptical back from the fifties through seventies when countries were disarming nuclear technology and using it for food. Even the word irradiation implies it becomes radioactive. This, of course, is completely false.
People are now concerned about the safety of produce. Irradiation is powerful against most pathogens, very much so against E. coli, somewhat effective with Salmonella, and quite effective against Lysteria as well. I’ve done work on ready-to-eat sandwiches.
It takes a stronger irradiation treatment to destroy Salmonella than E. coli. It’s a little bit hard to say with Lysteria, which is probably somewhere in between. Lysteria is not as much of a problem with fresh produce as E. coli and Salmonella. In most cases, you’re eating produce fresh, so there is very little you can do to kill dangerous pathogens at this point without changing the texture or taste.
What a fascinating interview. Obviously there is plenty of research to be done. But we do think that Dr. Prakash hits the nail on the head when she explains the contemporary, educated, opposition to irradiation: “Critics of irradiation are concerned it will lead to sloppy practices.”
Originally the opposition came from people opposed to “radiation” and, more specifically, these groups used the public’s lack of understanding of irradiation to fan fear and they made an implied threat to retailers to picket and protest if irradiated product was sold.
Today the whole world’s attitude is changing. Even many opponents of nuclear power have been rethinking their position in light of concerns for carbon reduction and global warming.
Years of experience have taught us that the extremists are not much of a factor. As we have mentioned here, here and here, Wegmans, for example, sells irradiated ground beef quite successfully. So there is no particular reason to think that if someone wanted to sell a line of, say, irradiated bagged salads or a line of clamshell tomatoes that had been irradiated, it would cause any mass disruptions.
The biggest concern of irradiation today is really that the pathogens typically trace back to excrement of some sort, and the idea is that consumers don’t want to simply have their produce “safe”, they also want it clean.
So the challenge for the industry in marketing irradiated product is likely to be persuading consumers that the industry still does all it can to make produce “clean” and then irradiates it for an extra margin of safety.
Obviously, issues of flavor, texture and taste have to be resolved, and there will be a marketing issue as well. Still, we wouldn’t mind seeing an allocation of, say, 20% of the research funds spent by the Center for Produce Safety dedicated to research in pursuit of a “kill step” for fresh produce.
Within the political paradigm which we operate, it is the only true solution.
Many thanks to Dr. Prakash for sharing her important work with us.