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visit MIT OpenCourseWare at ocw.mit.edu. MICHAEL SHORT: All right, guys. Welcome to the last
official day of 22.01. Can't believe we've
actually made it here. And you guys have
learned a ton about how ionizing radiation
does and doesn't affect different types of matter. If you've noticed that
the whole class has been kind of taking a slant
towards looking at issues in the public sphere
from things like hormesis to dose, to risk,
to power plants, today we're going to talk
about food irradiation. One of the main
reasons that we have all sorts of incredibly
safe food today thanks to ionizing
radiation, a lot of the myths and misconceptions and
science behind what does and what doesn't happen
when you irradiate food. And you guys are fully
equipped to determine not just is food irradiation
safe, but how should it be conducted? How should it not be conducted
and what would the effects really be? And with stuff that we did
the last few classes, actually looking up research papers and
discerning which sources are real and which ones
are, let's just say, not, for lack of a bunch
of four letter words, you can tell for yourselves
what sources are actually worth looking at. So just quickly go over the
basics of food irradiation and maybe five minutes before
we hit the primary sources. So the general idea
here for anyone that got into the reading,
which I'll pull up right here, is that we irradiate
food to do a whole bunch of different things. Can anyone tell me, what
are some of the reasons one might irradiate food? AUDIENCE: Bacteria like E. coli MICHAEL SHORT: Yeah,
gets rid of bacteria, other harmful organisms. It just kills other organisms. Like what? Like bacteria. Anyone else? AUDIENCE: Bugs. MICHAEL SHORT: Yes, insects. It's actually used to either
kill or sterilize insects so that they don't
breathe and let's say-- oh yeah, totally,
because the dose required to sterilize
something is usually a lot lower than the dose
required to kill something. Why do you guys think that is? Yeah? AUDIENCE: To sterilize
[INAUDIBLE] all you have to do is kill off your
reproductive cells. MICHAEL SHORT: That's right. And anyone remember what
those quality factors look like for those
reproductive cells? AUDIENCE: Much higher. MICHAEL SHORT: That's right. Let me bring it up. Let me go into the dose
dosimetry and background. I think it'll help to
actually see the numbers here. Let's go to the tissue
quality factors. There we go. Right at the top of the
list, reproductive organs. So it takes a whole lot less
dose to sterilize something like insects or other
bacteria or things, or I don't know if you
can say sterilize viruses. It's still kind of under
debate whether viruses are technically alive. They're right on that
edge of what people would consider alive or not. And there's still
a debate going on about what does
alive really mean. Yeah. You can sterilize the
insect population. For example, who here's
bought a bag of rice before, and who here has found
some little rice bugs in that bag of rice before? Are you serious? I must shop at cheap store,
I find them all the time. But the nice thing is if
you irradiate them then they won't breed and continue
to eat and breed in the bag and then you open
the bag and you've got a swarm of, I don't
know what those things are, rice weevils or something. I think I remember looking them
up once because I was like what is this thing in the rice? Yeah, it's gross. But that's why we
do food irradiation. Now, what else? What other reasons
might want to irradiate food other than to kill
or sterilize things in it? Yeah? AUDIENCE: Doesn't it
preserve like shelf lifes? MICHAEL SHORT: It does
preserve shelf life, especially of things like fresh fruits,
vegetables, seeds, legumes. Anyone have any idea why? Yeah? AUDIENCE: Well, it seemed like
that would be just because it kills things that eat it. MICHAEL SHORT: Yep. One would be it kills
things that eat it, but the other thing
is those plants have reproductive cells as well. Let's pick a good example. Anyone ever had really well
sprouted bean sprouts before? Like not the fresh ones,
but the really old ones? Not old like they've sat
behind the fridge or something. OK. AUDIENCE: Like super sprouted? MICHAEL SHORT: Yeah,
super crazy sprouted. AUDIENCE: The super
crazy sprouted. MICHAEL SHORT: Anyone
remember what they taste like? They are kind of bitter
and rather unpleasant. So one of the main reasons
for irradiating food is to prevent sprouting
and prevent germination because as soon as the plant
sprouts and starts to say like, all right, let's grow, starts
to consume its store of sugars, water, nutrients
and everything else and start generating
other flavors, which tend to be fairly off flavors. So another way that you can
keep things tasting good, even if they don't have bugs or
weevils or insects or viruses in them, is prevent
them from changing at all through their
normal metabolic processes. So it kind of freezes
the food in place. Well, since I
mentioned freezing, there's another
little caveat to that. At what temperature do you
think would be the best temperature to irradiate food? AUDIENCE: Cold temperatures. MICHAEL SHORT: You say
cold, and why do you say so? AUDIENCE: When you did that one
thing, the temperature'd grow. MICHAEL SHORT: Yeah,
let's bring it up. We talked about G-values
and temperature, and I think it's a
little further in. It's in the chemical effects. So I'll jog your guy's memory
a bit from just a week ago where we were talking
about G-values or the number of different
radiolytic byproducts of radiolysis byproducts
that are formed as a function of temperature. I'm not going to full
screen that because that's going to get all freaky. But you can see that there's
a whole lot more of them formed as a function
of temperature. What's not shown here
is what happens when this reaches 0 degrees Celsius? What happens to water
at 0 degrees Celsius? Just look outside,
what do we got? It freezes, OK. All these G-values
are calculated assuming the free species are
diffusing in liquid water. When you freeze the
food, you pretty much shut down diffusion. When you shut down diffusion,
do these chemicals react or not in a different way? Can they move to
find each other? No, they're frozen in place. You're stuck at the
diffusion coefficient in ice, which is
a whole lot slower than in free flowing water. So in this way, you can kill
whatever organisms are there even if they can survive
freezing by directly damaging their DNA, without altering
as many of the foods normal tastes, flavors,
colors, whatever. And speaking of
taste flavors colors, I want to bring up some
of the pseudoscience. It didn't take long to
find a couple of things on the internet
talking about how we shouldn't eat irradiated food. And to that I say,
well next time you spend five weeks
straight on the toilet you may be thankful
for food irradiation. So let's look to see
what sort of things could or couldn't happen
with food irradiation based on random
internet article. Again, not a useful source,
but let's see what they say. Damages food by breaking
up molecules and creating free radicals. That's true. What's the question we should
be asking though is not does it damage molecules? But what do you think? Yeah? AUDIENCE: Do the damaged
molecules have any effect? MICHAEL SHORT: Yeah. So one, do the damaged
molecules have any effect? Were those same damaged
molecules there to begin with? And the other question I
want to ask is how much? How much is always
the question you want to come back with
when somebody says isn't it true that radiation
does binary effect? Causes cancer, kills
babies, whatever you want? Sure, enough. But the question is how much? So there's a second
source top 10 reasons for opposing food irradiation. Let's go through these
a little bit one by one and look at some of the
references, which they're not all bad. So let's see. In legalizing food
irradiation we did not determine a level which
food can be exposed and still be safe for human consumption. So let's think about
what that actually means. We never hit that LD
50 or LD 10 or whatever dose we found that will
cause ill effects in humans. I would argue this
is a good thing. If we haven't had any documented
cases of people getting sick from food
irradiation and we already get the effects that we want
like stopping germination, sprouting, killing bad
things, then great, let's not go higher. Mission accomplished. Let's look at the
references again. Reference one, they
actually give a US code of federal regulations. Reference two, I
dare you to find what they were talking about. Various filings over
a period of 17 years. AUDIENCE: Isn't that dating
publication Federal Register? MICHAEL SHORT: I'm not sure. I think it might be
something more legit, but there may also be a
publication called the Federal Register. I doubt the Federal
Register publication has what's called filings, but these
would be more official filings. But yeah, they're somewhere
in the archives of somewhere. But at any rate-- AUDIENCE: [INAUDIBLE]
from class. MICHAEL SHORT: Again, I would
argue that this is actually a good thing. We don't know to what level food
irradiation can harm people. Now, let's think
about some of the ways in which if done incorrectly
it could harm people. Without me telling you
ahead of time-- and this we'll see who did a
little bit of the reading. --what sort of
types of radiation do we use to irradiate
food, and why? We have our choice of alphas,
betas, positrons, gammas, neutrons, heavy ions, et cetera. What would you use, and why? Yeah? AUDIENCE: Presumably
ionizing so you don't have to activate any
of the things [INAUDIBLE].. MICHAEL SHORT: So you
said presumably ionizing. AUDIENCE: Yeah, so you
don't activate them and you get
radioactive thiamine. MICHAEL SHORT: OK. Which of these types of
radiation are ionizing? AUDIENCE: Sulphur,
[INAUDIBLE],, gamma. MICHAEL SHORT: What do
you mean by ionizing? AUDIENCE: So they can lead to
ionizations in the material. MICHAEL SHORT: Oh. I would argue that every one
of these types of radiation can ionize. As we've seen, they
can all knock out electrons or other nuclei. But you're getting at
an important point. Can anyone help Alex clarify? because you're getting
onto the right track. Anyone? Yeah? AUDIENCE: [INAUDIBLE]. MICHAEL SHORT: OK. So you may not want to
use heavy ions or alphas because you don't want to
plant anything in the material. Are you worried about
implanting helium? What about iron? I mean let's say you
want to use carbon ions and the food is Carboniferous. That's OK. But what about some of
these types of radiation are quite different
from the others when we were talking about
everything from gamma to charged particle to
neutron interactions? What sort of things
might we look at as criteria to
determine whether or not we want to use this
for food irradiation? Stopping power. So stopping power, which is
related directly to range. So let's pick an
energy of around 1 MeV. How do you find the range
of 1 MeV alphas in food? Great. That's what I was
going to say too. You can either do
the calculations, or like most of us
actually do, we just run a quick simulation
that integrates all those calculations. So let's do that right now. So we will take one MeV
helium or 1,000k EV helium. We will approximate
food as water with a stoichiometry
of 2 to 1, a density of 1 gram per cubic centimeter,
and let's allow for-- I think I already know what
the answer is going to be. --10 microns. What are we getting for a range? 5, 6 microns for alpha
particles in water. How well would alpha
particles sterilize food? Not. So let's say you have
a chicken with diameter around 40 centimeters. The alpha particles would
penetrate the chicken to a depth of
approximately 6 microns. So alpha particles
are probably out. What else is out
based on range alone? Heavy ions. How far do you think ion ions
would penetrate into a chicken? Not far at all. Let's find out. Iron ions, I'm going to
shrink the scale to 1 micron. We actually kind of did this
on the homework, didn't we? I had you guys look at the range
of lighter and heavier ions. What I'm hoping is
that you'll have some sort of an intuition
for how far ions tend to go in material. So as you go heavier, does
the range go up or down? Range goes down. As we expect we're getting
just about 2 microns of chicken with heavy iron ions. So what could you do to get
those to penetrate farther? Yeah, so you could
boost the energy. So if you were to boost
the energy of the alphas-- let's see. First of all, with our
typical range relation where a range is roughly
proportional to kinetic energy squared, how much
more energy would we have to impart to the
alphas in order to get them to the center of the chicken? Well let's try and work it out. The range was about 6 microns
and an energy of 1 MeV and we want to get to
about 20 centimeters. Let's call that 6 centimeters. We're just going to use
this approximation for now. And if we want to go from
6 microns to 6 centimeters, that is four orders
of magnitude. So how many orders
of magnitude would we need to increase the energy
of the alphas to get through? OK. So we'd have to go to,
let's say, 100 MeV you said. Let's find out. We can just check this. So we'll switch back
to alphas at 100 MeV. This is already looking
to be fairly uneconomical. But this is physics,
so let's find out. OK. So we're at about
1.5 centimeters. And that's again
because at high energies this range relation changes
to about proportional to t for really high energies. So we know we're
going to have to get to around a GeV alphas in order
to food irradiate chicken. That sounds really expensive. Yeah. The proton cyclotron and
MGH is about 250 MeV, and we're talking an eight
or nine figure installation. Not worth it to irradiate food. What else might go wrong
with GeV alpha particles? What may you induce? Yeah? AUDIENCE: Bremsstrahlung
radiation. MICHAEL SHORT: Lot of
Bremsstrahlung radiation. We pretty much ignored
Bremsstrahlung of things like alpha particles
and protons. But once you get into the GeV
or tera electron volt range, you are going to get a
lot of Bremsstrahlung and shielding those x-rays
is going to be a mess. OK. So let's say we've
excluded alphas and ions for the purposes
of physics and we are left with batas,
positrons, gamma and neutrons. What next? AUDIENCE: Neutrons
are also expensive. MICHAEL SHORT:
Neutrons are expensive. You either need a reactor,
a spallation source, or a little pulsed fusion
device, two of which we have down the street. Let's say you had a
cheap source of neutrons. One of those, if you
build it and there's money to be made then they will-- no. If there's money to be
made they will build it, and if you build it, they
will come with their chickens for irradiation. Why else physically would
you not want to use neutrons to irradiate food? AUDIENCE: They
damage everything. MICHAEL SHORT: They
damage everything. That's OK, right? If they're damaging living
organisms more than the food itself, that's OK. But what do neutrons tend to do
when they interact with matter? And that's as specific as I
can make the question so far. The correct answer
is everything. Like what? Chris? AUDIENCE: Well, like Alex
said, they could activate-- [AUDIO OUT] MICHAEL SHORT: Yes. So that's when I said you're
getting on the right track. So thanks you guys for
doing a team tag answer. Yes, they can activate things
at pretty much any energy. For this I'm going
to jump to Janis. Like I said, I like
to do things live, so show you guys that we
could do it on the fly and respond to your
comments in real time. It is showing, good. OK. Though this is a skill
I want to make sure that by the end of
this class, which is about 35 minutes
from now, you guys will know to jump to Janis
and start looking for the right cross-sections
because you're going to need it for the rest
of your life career time at MIT. Pick probably two
out of the three if you guys are going to
be nuclear somethings. I'm definitely in a
different database right now. I was in incident proton
data for other things that will become apparent soon. Let's go back to
incident neutron data. We'll use the same
database that we've been using all the time, the
ENDF most recent database. Look at the cross-sections
and let's assume you had some iron in your food. You are irradiating red meat. Nickel, copper, iron. Pretty common isotope of
iron could be iron 58. Let's now go down
and find the z gamma the neutron capture
cross-section for iron 58. It's decidedly non-zero at
all energies, which means you're going to make iron 59. What happens when
you make iron 59? I don't expect you
to know, but where do we go to get the answer? Wall, yep, Tyree,
that wall, the table of nuclides, whatever you
want, or the Brookhaven table, whatever you want. The point is the
table of nuclides. Let's take a look at iron
59 and see what it does. It is not stable. It has a half life of
greater than 10 days. It's a beta emitter
and it beta decays to cobalt 59, which
is a stable isotope. So you would be creating
an unjustable source of beta particles. Nasty stuff. Let's see what those
beta particles would do. They have about
a 1.5 MeV energy. Let's look at the decay diagram. There are a few transitions,
the most likely of which would give a beta and a gamma,
the most two likely of which would give a beta and a gamma. So you'd be ingesting a
dual beta gamma emitter. Now, to find out how far
would those betas go, as in are they energetic
enough to escape you or not, what do you use? AUDIENCE: [INAUDIBLE] MICHAEL SHORT:
[INAUDIBLE] electrons. AUDIENCE: Calculations. MICHAEL SHORT: Back
to calculations. Or I want to show you guys there
is a database for everything and it's always on NIST. I wonder if any of you guys have
found these for the homework because I didn't use
them in the solutions, but they're quite useful. NIST has a database
called ESTAR, stopping powers for electrons
where you can simply say graph the total
stopping power or range for electrons
in elements or materials. Materials, let's call
food as soft tissue. They don't have that,
let's go to water. And it gives you the range
of electrons in grams per square centimeter in water. What do we have
to do to make this into an actual range
in centimeters? AUDIENCE: You divide by density. MICHAEL SHORT:
Multiply by density. Yeah, I'm sorry,
divide in this case. So you have the range in
grams per square centimeter. If you divide by
density you're left with centimeters on the top. The density of liquid
water is about 1. So in the case of water, you
can simply read off this table if you're talking water at
25 C. So a beta particle with an energy of
about 1.5 MeV has a range of about a
centimeter in material. Not something you'd
want to ingest because around 1 centimeter away
from wherever the betas end up they would do a
whole lot of damage at the end of their range where
they have the highest stopping power. So we for many, many
reasons, least of which is activation, neutrons are out. So we do not irradiate
food with neutrons because they will
induce radiotoxicity. So for anyone that
tells you, oh, don't you stick food in a
reactor to irradiate it, the answer is definitely not. You don't want neutrons nearby. So we're left with different
types of betas and gammas. From our study
right here we just found out that betas
penetrate about 1 centimeter into materials at 1.5 MeV. So how energetic do we
have to get them to get to the center of the chicken? If range is proportional
to t squared and our range at 1 MeV or 1.5
MeV is about 1 centimeter-- if we want to go
to 20 centimeters, about how much more
energetic do we have to get the betas to
irradiate the whole chicken? AUDIENCE: At least
10 times [INAUDIBLE].. Probably. MICHAEL SHORT: Let's
go with 10 times. Let's go to 15 MeV, and we
can just read off this chart. At 15 MeV we're
getting on about-- now keep in mind, this
appears to be a double log scale, so that right there is
10, that right there is 100. Yeah, we're getting
towards 10 centimeters. If we want to see
where it is at 20, the log marker line
is kind of missing, but it comes to about here. If we go down, we're
getting around 30 or 40 MeV. How reasonable does that
sound for linear accelerator? Fairly. It's not unreasonable. It would still be big. Yeah, it may not be efficient,
so we may not use betas to irradiate entire chickens. What if you're irradiating
strawberries that are roughly about a centimeter in diameter? How does a 1 MeV linac sound? We've got some of those. Yeah. We've got a 2.5 MeV linac
just down the street in building N40. So that's totally OK. You could use betas in order
to irradiate thin enough foods, food for which you
can reach the center with the range of the betas. Do you induce any
significant radiotoxicity? How do you find out? AUDIENCE: Experiments. MICHAEL SHORT: You
could run an experiment. Or what database would you jump
to to try to figure this out? AUDIENCE: Janis. MICHAEL SHORT: I
would jump to Janis. So let's go back there. Let's see if they have the
incident electron data. Yes, incident electron
data, the EXFOR database. It's good for charged particles. Let's look at iron 56. Let's say you're
irradiating red meat. I think this is just
total cross-section, so that's not going
to tell us much. It's also not loading and had
an error, and another error. Interesting. All right. Let's see if we have any other
interesting isotopes that have any good reactions. Guess not. All right. Well at any rate,
it's awfully difficult to induce radiotoxicity
with betas. There's another one
I didn't get into, which would be
protons, somewhere between alphas and betas
in terms of range and such. Does anyone know,
perhaps anyone that works in the vault, what happens
when you give very high energy protons? AUDIENCE: A lot of
gammas and neutrons. MICHAEL SHORT: Indeed. A lot of gammas and neutrons. The gammas, maybe no problem
at the irradiation facility; the neutrons, big problem. So find it again. We head to Janis, look at
the incident proton data. I've already scoped
this out and I know it's on the EXFOR
database of cross-sections. Let's go right back
up to our iron 56. So assume we're
irradiating red meat. What sort of
reactions do we have? Proton, n, something
with a few points to it. A-ha, a non-zero cross-section. So typically in the
range of five to 10 MeV, high energy protons will
start to create neutrons where a proton will come
in, a neutron will come out. So you would absolutely not
want to use protons above, let's say a safe
limit, of around 3 MeV. Then the problem
is what's the range of 3 MeV protons and stuff? Anyone have a
intuition for that? Pretty small. If you don't know generally
the order of magnitude, we'll head back to here to TRIM. We'll use 3 MeV protons. It's looking about a
millimeter of material. We're getting about
200 microns in. Not useful enough to be
useful for any sort of food irradiation. So protons again are out
for reasons of both neutron activation and range. AUDIENCE: When
people [INAUDIBLE],, it's like I sit next
to it all the time. MICHAEL SHORT: Sure. But what energy are the
protons that you're making? AUDIENCE: Well, I mean we
did a lot of low energy, but went down to like 10 MeV. MICHAEL SHORT: I highly
doubt you were sitting there during 10 MeV. AUDIENCE: I think the
highest we've gotten was probably 2 or 3. MICHAEL SHORT: Yeah. So 2 to 3 MeV, those proton
cross-sections jumped to 0. In fact, let me show
you that for a better-- kill the TRIM thing because
that'll fry the computer. Let's look at, I
don't know, carbon, where there's a whole lot
more data, natural carbon. There should be lots of
nice cross-sections here. So in goes proton-- maybe not for natural. Carbon 12 has over 100
different reactions. Something, n. Well, there's a lot of
reactions to sort through. Well, I don't want to waste
your time with that now. But anyway, hopefully
the cross-sections I showed you show you
that around 5 MeV or so you do start
to make neutrons. So if you can get
up to 10 MeV, that's why the vaults got that
forefoot thick door. You don't want to be in
the room when that happens. AUDIENCE: When we do a
lot of protons in class is not shielded. MICHAEL SHORT: Yes. But the class accelerator
only goes up to about 2 MeV. Yeah. And that's perfectly safe to
be standing around there for. AUDIENCE: We have downstairs
we can't next week because interlock. MICHAEL SHORT: Yep. Because of interlock, but not
because of physics, right? AUDIENCE: I'm in both. MICHAEL SHORT: OK, fair enough. Cool. So now we're left with gammas. Gammas work pretty well. They have very,
very long ranges. Even the concept
of range of a gamma is kind of a funny thing
to say because they undergo exponential attenuation. So you want either a high
enough flux of gammas that their low attenuation
won't matter or you use a lower energy gamma ray. So cobalt 60 irradiators that
give off those 1 and 1/2 MeV gammas are quite commonly
used for this sort of thing because the 1 and 1/2
MeV gammas will get through just about everything. You just need a
whole lot of them. Has anyone here seen or heard
of the cobalt irradiator downstairs in the
basement building six? We got one of these
things actually. It's just a sealed
source of cobalt. And the way you start
irradiation is you simply open the door
and the irradiation stops being shielded enough. Now, what things could go wrong
with super high energy gammas? AUDIENCE: Ironizations. MICHAEL SHORT: Ironizations
is what you want, right? You want to ionize
the water and the DNA of the bacteria or
the germinating cells so that they get destroyed. What else could you induce
with super high energy gammas? AUDIENCE: [INAUDIBLE] electrons. MICHAEL SHORT: That's another
form of ionization, right? So that's a good one. Why don't I show
you a quick thing? Let's go to incident gamma data. I think the EXFOR database
will be pretty good. Let's go back up to iron again. We'll go with our
red meat example. Gamma, neutron. Anyone heard of gamma
induced neutron ejection? High enough energy
gamma rays will actually cause neutrons to be emitted. So gammas are a definite
yes from the point of view of physics. They're also going to
have to be less than about 5 MeV because once you
get to around 5 MeV, or in the case of
iron 56 10 MeV, you end up with a non-zero. And actually fairly
significant like 0.1 barn cross-section for a gamma
goes in, a neutron comes out, and that neutron comes
out at whatever energy. It activates what's
nearby and makes all sorts of nasty isotopes
that decay the way they will. Do you guys remember too
from the neutrons discussion about photofission, the idea
that a gamma ray can induce fission of a heavy nucleus? So if there's any traces of
uranium in the food, which there always are, whatever,
what you don't want it to do is then make a whole
bunch of fission products because even a couple parts
per million of uranium which might be no big deal could
be a big deal if you turn it into fission products
instead of plain old uranium where it's just a heavy
metal, like lead, whatever. We can deal with a tiny
bit of lead in our food. Totally. Yeah, OK. So while looking through
these internet studies talking about-- I don't like this kind
of argument number four, irradiation encourages
filthy conditions. I don't think that's a
fault of the irradiation. I think that's a fault of the
people who are like, oh cool, physics means that we
can relax our standards. These are separate arguments. And going through all these
things that, frankly either are false, are true,
but the question is how much, and are true
to such a small degree that it barely matters. And wading through a
lot of these things, let's say, PhD thesis,
articles in the ecologist, a lot of other FDA
papers, various filings, from the '60s came upon actually
a really useful document, this World Health Organization
study on the wholesomeness of food irradiated with
doses above 10 kilogray. It's modern. It was done by a peer
reviewed study group. It was commissioned for
a major organization, so I pulled it up. Yeah. It's like, OK, there's a
legit reference in here. I recommend you guys
look through this. It's quite fascinating
how many studies have been done on rather
higher irradiation doses. So you can usually get away
with stopping germination at around a kilogray or so,
rather low dose of radiation. The highest dose anyone would
use is about 50 kilogray. They specifically looked at the
highest order of magnitude dose that we use for food
irradiation and looked not just to say are there ill effects,
but what are the ill effects? What are the other
compounds that are made, and do they matter in the end? And I want to walk you guys
through a few of the bookmarks that I found pretty fascinating. I asked you guys about G-values
at low and high temperature. Here's a great plot
showing that right there. This is food irradiation done
at 20 and minus 40 Celsius to look at the amount
of ammonia, nitrates, ferrocyanides, things
that you might not want, and look at the difference
between irradiating at 20 C and minus 40 C. Enormous. Why is that so, physically? AUDIENCE: Diffusion stops. MICHAEL SHORT: Exactly. Diffusion stops when you
cease to have a liquid. It doesn't stop completely,
but the diffusion constant of anything and a
solid it's going to be a whole lot slower than
that same anything in a liquid. And so this way you
can destroy the cells without all of the
radiolytic byproducts going around and damaging other
food molecules and other food cells. Then we got into the question
of off smells and funny sorts of changes. So one of the comments said
can change the flavor odor and texture of food,
pork can turn red, beef can smell like a wet dog,
vegetables could become mushy, et cetera, et cetera, et cetera. This review of studies
actually looked at what compounds are formed in
which foods, and by how much? The only thing they didn't
tell you is how do they smell? So I looked up a few of those. They looked at hexanes as
a function of fat content for a rather high
dose for 10 kilogray, or at least here everything is
in normalized per 10 kilogray. So this is the yield of this
compound in nanograms per gram. Does that sound like a big deal? It may not sound
like a big deal, but a lot of these
odiferous compounds are detectable by the human
nose in parts per billion. So they actually do matter. And I looked up to
see what sort of smell do hexanes typically have? The word was petrolic, smelling
like petrol or gasoline. Might not necessarily
be something you want. And it is true that fat
compounds when you break up these, let's say, fat
molecules, which usually contain three fatty acids,
those fatty acids themselves are very aromatic. You've heard that
expression fats where the flavor is, right? A lot of it is not just due to,
well, if you just eat butter, it's not that flavorful. Anyone ever tried? I'm glad I'm not the only one. OK, good. But where fat really comes
into play is when you heat it and it undergoes all sorts
of different chemical reactions with the
food nearby, liberating some of the fatty acids. It's part of why lamb smells
like lamb and nothing else, is fat's where the flavor is,
and 90% of flavor is smell. You've only got
five or six tastes I think that's still
under the debate, but you can smell thousands
of different compounds. And so they actually matter. So I started looking at
some of the other ones. Heptadecadiene in micrograms
per gram fat per 10 gray for foods containing
a lot of linoleic acid. The smell, Carrion
beetle sex pheromones. The sex pheromones shouldn't
be what turns you off, it should be the Carrion beetle. What is Carrion? It's the beetles that
feed on rotting meat. So this is the juice that
rotting meat beetles secrete to attract other rotting
meat beetles nearby, to use polite language. It's probably something that
you don't want in your food, or is it? Does anybody know what
makes pork smell like pork? Is what? AUDIENCE: Do I want to know? MICHAEL SHORT: You're
going to find out. Who likes pork here? Awesome. I'm going to ruin your day. There's a compound
called skatole. Can anyone figure out
from the root of the word? Yeah. Anyone ever heard of that
wonderful barnyardy smell from a cut of free range pork? Anyone heard this term before? Just raise your hands. Anyone heard the nice
pork barnyardy smell? OK, a couple of people. That barnyardy smell is
parts per trillion or parts per billion of skatole. So tiniest littlest bit of poop. Yeah. The same sort of
compounds that you find in scat in
incredibly small amounts contribute to the wonderful
flavor of really good pork. So just because
these compounds are made in higher amounts with
higher amounts of fat or dose doesn't mean that they're
necessarily off flavors. But it is kind of
hilarious to see what other places
do you tend to find high concentrations of these? The next one down,
hexadecatriene from irradiation of muscle. The one paper I could find
that talked about this in a cocktail of
smell compounds comes from the odiferous
defensive stink glands of red something beetles. Yeah, sounds horrible, right? So if you stopped
there you might think, great, so radiation produces
odiferous defensive stink gland compounds. But as we know,
pork smells great. We don't necessarily know
in what concentrations-- what is it? --hexadecatriene
would smell good or smell bad to the human nose. It's just no telling. There's some compounds in any
amount if you can detect them they're terrible. There's some compounds
that go from bad to good. There's some pounds that
go from good to bad. Anyone ever smell someone that's
slopped on perfume before? Would you describe
the smell as good? No. Perfume relies on lots of
different compounds in very, very small concentrations. It's supposed to be subtle
and enhance your own body chemistry. You're not supposed to
smell like a perfume factory explosion. So another sort of
real life analogy where too much of a
good smelling thing can smell really bad. Yeah. And so then going on from
the various odiferous compounds where a few other
points I wanted to-- oh no, there's another one. OK. Seems like the production
is pretty much linear with either dose or with the
abundance of the precursor normalized dose. This one you tend to
find in deodorants. What was the name
of this compound? Propanediol type. Don't know the structure
because I'm not an organic chemist, but things
you might find in deodorant. Again, no telling
whether or not this would be good or bad
in food and how much. That's always the question
I want you to remember. If somebody asks, isn't
binary effect bad? Isn't meta tag
binary effect bad? The question is
depends how much. Yeah? AUDIENCE: Do these like
graphs show how much more more there was afterwards or
just like how much there is in general? MICHAEL SHORT: They do. It shows the dose normalized
yield per 10 kilogray in micrograms per gram. So it shows that depending
on how much of whatever precursor, in this case
enzyme inactivated muscle there was, how much relative
amount of this compound existed. What these graphs
are telling us is they're pretty much
all linear and they're pretty much all the same for-- I saw that as human for
a second, holy crap. My heart just skipped a beat. --ham beef, chicken, pork. Oh man. Anyway, going into
the conclusions, which again are strikingly different
than the internet article would have you believe, I wanted
to point things out. Interesting. Irradiating moist foods while
frozen in the absence of oxygen significantly decreases overall
chemical yields by about 80% So it's interesting you
can irradiate something to 50 kilogray at minus 30 C
and it does the same chemical change as 10 kilogray at
room or chilled temperatures, but you do that much more
damage to the organisms. So yeah, there you go, better to
irradiate at cold temperatures. And there's a few other
interesting conclusions. These radiolytic compounds, are
they found in food otherwise? Virtually all the
radiolytic products found in high dose irradiated
foods are either naturally present foods or produced in
thermally processed foods. Before food irradiation
you had heat sterilization. In fact we still
do for quite a bit. And folks, a lot
of times we'll talk about the amount of nutritional
decline, the amount of lack of nutrition from
irradiated foods, and they'll just say
it's a bad thing. That's not the right
fact to see here. Food preservation tends to
lower the nutritional content. And there's a few neat tables
I want you guys to look at. In terms of
macronutrients, do you lose the protein, the
fat, the carbohydrates from in this case,
gamma-irradiated mackerel, as a function of dose? Does anybody see a trend here? Take a sec to look
at the numbers. AUDIENCE: Seems like
it bumps in the middle. MICHAEL SHORT: It does seem
like the nutritional content goes a little bit up with
small doses, doesn't it? Would you necessarily believe
these data at first glance or at face value? What's missing
from this data set for you to draw a statistically
significant conclusion? AUDIENCE: Error bars. MICHAEL SHORT:
Error bars, right. If this is the
graph of, let's say, protein content versus dose
in gray and this is protein, the data appear to do
something like this. If the error bars
are like that then you can't draw any
meaningful conclusions. So one would have to
go back to the study to see hopefully they
actually had error bars in their measurements. So what I can
conclude from this is macronutrients
basically don't change with up to the highest
dose of radiation that we give to any food at all. What about the micronutrients? What about things like vitamins? They do go down somewhat,
and they're pretty linear. They're fairly linear with dose. It's not much to
be disputed there, is yes, irradiating
food does destroy some of the vitamins
and not the minerals. Why wouldn't gamma irradiation
destroy minerals in food? What's an example of a mineral
that you need for survival? AUDIENCE: Iron. MICHAEL SHORT: Iron. AUDIENCE: Calcium. MICHAEL SHORT: Calcium. Yeah, bunch of other elements
or inorganic compounds. Why does food irradiation
not affect mineral content? AUDIENCE: If you use low enough
energy gammas it's just not going to change paratonic. MICHAEL SHORT: That's right. Yeah. You stay below 5 MeV gammas
and there's literally no change in the elemental
composition of those minerals. The vitamins, however,
tend to be more complex organic compounds
that can be damaged. And one of those big
ones is thiamine, better known as vitamin B1. So irradiated food is a
little bit less nutritious, but they give a pretty
good explanation. Let's see. Think that's later
in the conclusion, so we'll get to that. Conclusions on nutrition. Yeah, there we go. So in this case, what
they're saying is, well yeah, it takes away some thiamine,
but irradiated food does not constitute the major
source of thiamine in the diet. So even though it does
reduce the amount of thiamine that you get, it
doesn't make a dent in your overall
nutritional uptake unless you eat nothing
but that irradiated food. Does anyone remember when the
last case of scurvy in the US happened? Talking about single food diets. Happened right here at MIT. It was a while ago. I think by now it would have
been over 10 or 15 years ago. There was a student
that decided I'm going to have the cheapest
food budget ever and live off nothing but instant
packs of ramen. Now, this is already a
nutritional nightmare, but it got worse and worse. So it was the ramen, the
flavor packs and water, and that's just what this
person ate the whole time. And then they decided,
you know what? I don't really need
the flavor pack because that's just a
bunch of sodium, taking out whatever little
micronutrients were left. And then the next logical step
was why bother cooking it? And a few weeks later massive
constipation and scurvy ensued, which is a disease
you don't see anymore, from a deficiency
of vitamin C. So if you're only eating one
food to begin with you've got other problems have nothing
to do with food irradiation. Yeah? AUDIENCE: I'm not even surprised
that the last case of scurvy was an MIT student. MICHAEL SHORT: I'm not
surprised at all either. I'm surprised Soylent
wasn't invented here. It seems like the kind of
thing that someone here would have done. Anyway, let's take a look. Ah, irradiation versus
heat sterilization. From a nutritional
viewpoint, irradiated foods are equivalent or superior to
thermally sterilized foods. Why do you guys
think that might be? AUDIENCE: They're
really sterilizing it with denaturing most
of the proteins. MICHAEL SHORT: Indeed. So you'd actually get
some macronutrients to disappear if you start to
denature or break down those, and even for micronutrients. The idea here is that the
amount of micronutrient content will go down roughly
linearly with dose. What happens when you reach the
temperature of destabilization of those foods? AUDIENCE: [INAUDIBLE]
dropped them. MICHAEL SHORT: Yeah,
all of it goes away. Once it's temperature
unstable, if you keep it at that temperature
for long enough you'll destroy pretty much
all the nutritional content. So if the choice is between do
you heat or do you irradiate, irradiating does less
damage in the end. Anyone here ever had an
MRE, a Meal Ready to Eat? How do they taste? AUDIENCE: They're not great,
but they're not awful. MICHAEL SHORT: But they
do last for like decades, like many decades. There's an entire
channel on YouTube of this guy that just eats MREs
from further and further back. I think he's made it as
far back as the Civil War and ate actual moldy hard
tack from the Civil War. But my point here is
that all the way back to definitely to World War II
and perhaps beforehand, MREs were sterilized with heat. You put something in a metal and
plastic lined bag to keep out all other organisms. You heat it for
long enough to kill every single other organism
and they last for decades. And the question is, do you
want to eat what's in the bag? If you want some fun
between studying for finals listen to this guy's reaction
as he eats some of these 60 or 70-year-old MREs from World
War II of the Korean War. AUDIENCE: Why would they
subject themselves to this? MICHAEL SHORT: I don't
know, for attention. AUDIENCE: [INAUDIBLE] gets stung
by a really painful insect, and I will say why? MICHAEL SHORT: Yeah. At any rate, canned
food you can tell has an awfully
different taste to it. A lot of these cans
are heat sterilized. They're pasteurized
and the heat themselves generates a lot of
off flavors that you can tell the difference between
fresh and canned green beans in taste, texture, color,
mushiness, whatever other qualifiers you give to food. So to those opponents
of food irradiation, I'd say consider
the alternatives, either heat
sterilization or spending most of your waking
hours in the bathroom. AUDIENCE: How do you like
thermally sterilize meat without cooking it? I've always been really
confused about that. MICHAEL SHORT: Yeah,
you can't necessarily. There are also spores
of bacteria that are incredibly heat tolerant. So you can't necessarily
sterilize meat without cooking it. So the best thing to do is
to cook it, sealed in a can, or sealed in something
and then don't unseal it until consumption time. Yeah. There are other things that you
can sterilize without cooking them, like milk. Milk is pasteurized. You heat it to a
temperature that's sufficient to kill most
of the microorganisms not to sterilize it, but
to increase its shelf life so that it takes months instead
of hours for that microorganism population to bloom
and ruin the milk. I'm sure everyone here has
smelled spoiled milk before, right? Doesn't matter how
pasteurized it is. Has anyone opened a carton of
expired milk after its shelf life? AUDIENCE: One time I
poured it into my cereal. MICHAEL SHORT: Yeah. That was a study in
two phase flow, right? Liquid, solid. Yeah. Yep. So there is some proof right
there, a few bacteria survive. It's the same thing
with food irradiation, you need an enormous
dose in order to actually sterilize the food. So this is usually the
only option for folks with extremely compromised
immune systems in hospitals is if you want to give
them actually sterile food that's actually
palatable, you irradiate it to like 50 kilogray. And that kills just about
every single organism including the long lived spores. One other side benefit
of food irradiation is the cells that survive have
been blasted by radiation. They tend to be a lot weaker and
more sensitive to heat and pH and temperature-- heat,
temperature, the same thing. --so that the cells that make
it through the food irradiation are more susceptible
to damage and then it helps make things
a little bit safer. I'm trying to see if there's
any other conclusions. Oh yeah, the old who
cares about thiamine. It's unlikely however, that the
irradiated foods of this type would constitute a large
enough proportion of the diet to compromise the dietary
requirement for thiamine. And this is coming from the
World Health Organization. If there's any
organization you think you can trust about health
everywhere, it's the WHO, it's these guys. And I don't think we have time
for more of the conclusions, however I will post this
document up to the learning module site so you
guys can peruse at your leisure along
with the bookmarks, unless I've done it already. Want to open it up the last
two minutes to any questions you guys may have about
anything, including final logistics, how it's
going to all come down, the review session on Friday,
whatever you guys want. AUDIENCE: So the review is
9:00 to 10:00 on Friday? MICHAEL SHORT: Yep. The review is 9:00
to 10:00 or 10:30, whenever we finish on Friday. I'll email out with a
room once I secure one. Yeah? AUDIENCE: Where do they
usually do food irradiation? MICHAEL SHORT: There are
gamma irradiation facilities where they've got these
cobalt 60 or cesium sources. No, this would be
processing centers. Yeah, I mean you
can't normally own one of these giant
cobalt sources so. These would be specialized
processing centers. Yeah? AUDIENCE: So is
this usually only done for foods coming
in the US from outside? MICHAEL SHORT: Oh no. It can be done for foods grown
within and for the consumption in the US too. If you want to extend its shelf
life by small or large amounts you can do it for
anything, but there are a number of different
types of produce that can only be imported
because of food irradiation. One of these that I
was delighted about was mangosteens from Thailand. Mangosteens probably
almost no one here has ever even heard of or seen. I'm surprised anyone has. OK, wow, two, that's a record. They're usually only found
in South or Southeast Asia. They don't tend
to last very long and they tend to be
riddled with parasites. But one time out of two that
I've opened up a mangosteen, a whole bunch of bugs
started crawling out. You'd imagine that
the US doesn't want that imported into here. But in 2005 Thailand started
irradiating their mangosteens. They were approved for
sale in this country and you can find them at H
Mart now down the street. Even food from Hawaii has to
be irradiated for consumption in the continental US. Why do you guys think that is? AUDIENCE: Human species. MICHAEL SHORT:
According to the USDA, Hawaii is effectively
a different country when it comes to the
sorts of parasites you'd find in the food. It is a part of the US, but
it is not agriculturally a part of the continental US. It's got its own unique
parasites and pathogens and organisms and critters. So a lot of things
coming from Hawaii have to be irradiated
for consumption in the continental US. So yeah, food irradiation
helps food commerce go around. Any other questions? Yeah? No, it's you. AUDIENCE: What percentage of
food actually gets irradiated? MICHAEL SHORT: I don't know
what percentage of food gets irradiated. It especially
depend on the type. There's some things
that don't need it. There's some things
that do need it. I'd wager a guess to say that
more imports get irradiated than domestic consumption stuff,
but I don't know that for sure.
