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I'm considering exposing raw fish slices to a UV lamp to kill bacteria before making it into sushi. Would this help? Is there a practice of doing this? And what could be the drawbacks, if any?

UPDATE Thank you very much for your answers. A couple of points to clarify. I am talking about:

  1. Using UV-C light wand
  2. Using it on freshly defrosted fish, that is in addition to freezing, not instead of it
  3. The goal is to further reduce risk of bacterial infection, not to completely sterilize the fish, as that wouldn't be possible

Furthermore, while digging on the Internet I found this:

For some types of food this [surface treatment] may well be sufficient, for example, muscle flesh from a healthy animal immediately after slaughter is, for all intents, sterile. Where contamination does occur, it will be as a result of contact with contaminated surfaces or fluids and this will initially manifest itself at the surface.

The efficacy of UV surface treatment will be strongly influenced by surface topography. Crevices, and similar features, of dimensions comparable to the size of microorganisms (i.e., a few microns) may shield microorganisms from potentially lethal UV rays and enable them to survive. This was cited in recent work as the reason why the UV treatment of fish fillets from a smooth-fleshed species was more effective than that of a rough-fleshed one.

This seems to imply that what I proposed had been tried and even proven somewhat effective.

I have not however found any mentions that UV exposure can cause changes in raw fish that would make it harmful to eat. In other words to make fish less safe than before. If anyone saw such effects being mentioned, please let me know (preferably without a pay wall).

Thank you again.

Community
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Levi Haskell
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    With raw fish, you also need to worry about parasites (e.g. worms). Which are presumably harder to kill than bacteria - longer exposure times, etc.. – Bob Oct 20 '16 at 02:58
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    Freezing at -20F for 24 hrs should take care of that – Levi Haskell Oct 20 '16 at 02:59
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    Assume that UV will do nothing about parasites or parasite eggs unless proven otherwise.... – rackandboneman Oct 20 '16 at 08:08
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    Just buy fresh fish and use it immediately. – OrangeDog Oct 20 '16 at 12:40
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    Just to clarify - there are _two_ possible uses for UV here: Keeping sterile food sterile, or sterilizing already contaminated (but not spoiled) food. The two are fundamentally different: Since sterile food gets infected from its environment, surface treatment can be effective prevention. Sushi is unlikely to get infected from the inside. But once bacteria have gotten in, a surface treatment no longer is sufficient. – MSalters Oct 20 '16 at 23:06

4 Answers4

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That is an interesting idea, but I would not recommend it.

It is true that UV light is able to kill microorganisms, and it has been used to treat water for quite some time now. It has also been used to treat some types of juices, and is even used in the food industry (factories). It is an alternative to pasteurization, since it provides an alternative way to killing harmful bacteria without altering the food taste.

However, the uses of UV light in solid foods (and even liquids) do require extensive study about the food properties. This means that, in order to effectively use UV light to kill bacteria in fish, one would have to seriously study how it interacts with the specific type of fish you plan on using.

I am not sure if such study for fishes exists. So, it is best to avoid using this technique, since it could potentially make people sick.

A good read about this topic is this academic paper, entitled "Review: Advantages and Limitations on Processing Foods by UV Light".

Guilherme Salomé
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    Very interesting. Could you provide more links to evidence of (potential) dangers of UV light processing of solid foods coming from UV exposure itself? Preferably without a paywall. – Levi Haskell Oct 20 '16 at 00:30
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    @LeviHaskell The #1 danger is that the light won't penetrate as deep as bacteria do, so you'll think it's disinfected but it won't be. – Agent_L Oct 20 '16 at 10:45
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    @Guilherme do you not recommend it because it may not be effective enough or because it can make the fish *more* dangerous to eat? – Levi Haskell Oct 20 '16 at 20:24
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    @LeviHaskell hey I didn't notice there was a pay wall, sorry about that. I think you can find similar articles on google scholar. I believe using the UV light in addition to the freezing technique would not make the fish dangerous to eat, but it might be an overkill, since freezing is already good enough. In any case, I think your initiative is very nice, just do a lot of research and be careful with these UV lights. – Guilherme Salomé Oct 20 '16 at 20:35
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Partial answer, but here are some important facts before someone gets hurt:

  • Germicidal UV (UV-C) lamps are NOT the same as blacklight/anti-counterfeit/tanning (UV-A/UV-B) lamps.

  • Parasites and microbes are two distinct risks with raw fish, and need different measures.

  • Something (the bulk of the food, or packaging around it, or material used to protect skin or eyes) being transparent or opaque to visible light and/or UV-A/UV-B says nothing about it being transparent or opaque to UV-C.

  • Strong UV-C needs careful handling since it can quickly cause eye irritation or even eye injuries.

rackandboneman
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Limitation with the UV wand is that is only kills bacteria on the surface. If bacteria is present on the surface of the fish then it is could also be present inside the fish.

If the bacteria requires oxygen then then it would not penetrate far. According to this not all bacteria requires oxygen.

It would likely reduce the risk.

paparazzo
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  • 1. Wouldn't UV penetrate a thin slice of fish, at least somewhat? – Levi Haskell Oct 19 '16 at 21:46
  • @LeviHaskell You think the bacteria has only penetrated *somewhat*. – paparazzo Oct 19 '16 at 21:50
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    2. Isn't the safe center grilling temperature for stake lower (130F) than that for ground meat (160F) because bacteria is likely to be on the surface of a whole cut, while ground meat could be contaminated all the way through due to grinding? Shouldn't the same be true for fish? – Levi Haskell Oct 19 '16 at 21:51
  • @LeviHaskell Yes bacteria starts on the surface. If I change likely to could would you be OK? – paparazzo Oct 19 '16 at 21:54
  • Thank you for your edit. Bacteria also probably require time to penetrate deep, and freezing/refrigeration should slow it down considerably. I was not taking about __sterilizing__ the fish. My question was whether it would reduce the bacterial load to make the food safer to eat. – Levi Haskell Oct 19 '16 at 22:05
  • Also we're talking about exposing the fish slices to UV light, not the whole sushi. – Levi Haskell Oct 19 '16 at 22:06
  • Yes it would reduce risk but your wording is "disinfect". – paparazzo Oct 19 '16 at 22:09
  • "Disinfection only reduces the number of microorganisms and does not completely eliminate them" while "Sterilization is a treatment that frees the treated object of all the living organisms" according to: http://www.differencebetween.com/difference-between-sterilization-and-vs-disinfection/ – Levi Haskell Oct 19 '16 at 22:22
  • @LeviHaskell I am not trying to argue with you. Do you want me to delete the answer? – paparazzo Oct 19 '16 at 22:23
  • Not at all. I appreciate it. I'd only suggest you change the word "sushi" to "fish" and maybe add that "it would likely reduce the risk", but only if you agree. Thank you – Levi Haskell Oct 19 '16 at 22:28
  • The kind of UV light used for killing bacteria is readily absorbed by tissue and even the atmosphere (after all, that's why it can be used to kill bacteria). UV isn't a magical "kill all life" kind of thing - you need enough energy to break important bonds (like the ones in DNA), and a high absorption. That necessarily decreases the penetration depth - the two go hand in hand. There's little data easily found on this, but it seems that if the UV light doesn't feel warm to your skin, it's not going to penetrate even a millimeter deep (which is why you get skin cancer and not liver cancer). – Luaan Oct 20 '16 at 08:44
  • If the goal is to reduce the quantity of bacteria on the surface of the fish, you can achieve the same thing by washing in running water. – barbecue Oct 20 '16 at 13:24
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UV lamps only kill bacteria on the surface of food, not in the food itself. If there are harmful bacteria inside the fish then no amount of UV will make it safe. If there are no harmful bacteria inside the fish then the only concern is harmful bacteria on the outside. If there are harmful bacteria on the outside (ie the surfaces of the prepared fish) after preparation will be there because it was exposed to it during the process of preparation. You can make sure the surfaces of the fish is safe by being clean, if you have clean surfaces, knives and hands then UV won't be needed. If UV is needed to make the fish safe then your preparation is at fault.

GdD
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