Here's a web site that describes the production of suspected
carcinogens in flame-broiled beef:
Nutrition Action Healthletter.
"While PAHs seem to be limited to grilling or barbecuing, another
group of risky chemicals, heterocyclic amines (HAs), occurs more
frequently in broiled to and pan-fried meats. HAs are formed from the
burning of amino acids and other substances that are in all meats.
In general, the hotter the temperature and the more well done the
meat, the more HAs.
"Unfortunately, researchers don't yet know enough to determine if HAs
in broiled and other meats pose a greater risk than PAHs in grilled
meats."
http://www.cspinet.org/nah/grilling.html
A passage in the PNAS article by Brown et.al. leads me to suspect
that heating at high temperatures could produce the toxic agent:
New studies on the heat resistance of hamster-adapted scrapie agent:
Threshold survival after ashing at 600°C suggests an inorganic
template of replication.
"Exposure of undiluted inocula to 600°C (which completely ashed the
tissue) almost completely destroyed infectivity: no transmissions
occurred in 15 hamsters inoculated with the 5-min specimen, but five
transmissions occurred in 18 animals inoculated with the 15-min
specimen. This apparent inconsistency and the prolonged and variable
incubation periods in the five positive hamsters (174, 186, 193, 205,
and 313 days) suggest that infectivity in these inocula was near the
point of extinction. Heating at 1,000°C for 5 min produced total
inactivation."
http://www.pnas.org/cgi/content/full/97/7/3418 [full text]
However, you would have to explain how it could be that the 5-min
heating at 600 C was able to destroy infectivity while the 15-min
heating restored it. From the phrasing here it appears the 5-min and
15-min samples were different. What would really clinch the idea that
15-min heating *caused* infectivity is if they used a sample first
heated to 5-min and found no infectivity then continued heating that
same sample and found infectivity when heated to 15-min.
You would also like to get similar results at other temperatures.
However, they found no reduction in infectivity at the 5 and 15 minute
times for the 150 C and 300 C temperatures. However, one presumes you
would get some change in infectivity for heating at these temperatures
at longer times.
The question is would you get the same result of no infectivity when
heated for some time at a particular temperature but restoration of
infectivity when heated to a longer temperature?
I also found interesting the comparison the authors made to survival
of some bacterial spores to high heat:
"The best-studied examples of microbial heat resistance are found
among bacterial spores, which typically are used to test the
efficiency of autoclaves and incinerators: wet spores of Bacillus
subtilis and Serratia marcescens have been shown to resist brief
exposures to temperatures between 270°C and 340°C, and some viability
of dry spores persists after exposure to 370°C (21)."
In earlier studies of survivability of some microbes in space, it was
found a particular bacterial spore that had orders of magnitude
greater survivability to dry heating than other bacteria, Bacillus
xerothermodurans:
From: Robert Clark (rgclark at my-deja.com)
Subject: Space ready spores?
Newsgroups: sci.astro, sci.physics, sci.bio.misc, sci.astro.seti
Date: 2001-12-13 14:13:06 PST
http://groups.google.com/groups?th=53ceb8a4314963de
This spore retains 10% viability even after heating for 2.5 hours at
150 C. Then much higher survival would be expected at only 5 to 15
minutes. Given the much higher survivability of this spore than other
bacteria it would be expected some fraction could survive exposure 370
C for several minutes.
In the refs. I cited in the post there was still an unresolved
question of how the spores were able to survive these high
temperatures. One possibility could be the unusual honeycombed coat
possessed by the spore. If the interior of the spore is encased in
this coat shaped somewhat like a buckyball then heat might be
communicated to the interior only through the thin sides of the coat,
thus limiting the amount of heat communicated to the interior.
I'm thinking here of the case for example of space shuttle tiles that
can be held at the edges while white hot at the interior.
Bob Clark
rgregoryclark at yahoo.com (Robert Clark) wrote in message news:<832ea96d.0203302325.4aa27742 at posting.google.com>...
> Given the high resistance to heat and radiation of the infectious
> agent in BSE type diseases has there been any research into the
> possibility that high heating or radiation might cause the protein
> deformations seen to accompany these diseases?
> I'm thinking of the reports that high heating of beef can produce
> cancer causing chemicals.
>> Bob Clark
>>enigl at aol.com (Davin C. Enigl) wrote in message news:<3ca62a11.27924152 at news.earthlink.net>...
> > On Fri, 29 Mar 2002 15:10:21 -0600, "Paul F. Dietz"
> > <dietz at interaccess.com> wrote:
> >
> > >"Davin C. Enigl" wrote:
> > >
> > >> Yet, I read prions survive 1000C for 1 hour, and higher temperatures
> > >> that would normaly "ash" naked amino acids.
> > >
> > >I seriously doubt prions survive unchanged for 1 hour at 1000 C.
> > >Perhaps they get converted to a carbonized nanolump that
> > >has a similar shape and can initiate the same conformational
> > >chain reaction in the affected proteins.
> > >
> > > Paul
> >
> > Well, never-the-less the I read article claimed the prion was still
> > caused BSE, so I was not affected very much if at all -- certainly not
> > to the point where anyone would claim they were denatured.
> >
> > This "survival after ashing" was also stated as a fact, by Paul
> > Brown's research at the US National Institutes of Health.
> >
> > As you know, catalysts like prions must be quite specific via the
> > "lock and key" theory. Therefore, I can not see how a break in say,
> > the beta sheet conformation could still cause disease. The alpha
> > helical form (normal) is easily denatured however.
> >
> > Also, sterilization by heat alone is not enough to make me comfortable
> > . . . we add a 1.0 M NaOH flood over the item to be sterilized and
> > then autoclaving at 132 C for 5 hours is our current standard, --
> > UCSF recommended this some years ago. I am not sure what F sub-zero
> > at 132C that works out to for 1000C for 1 hour dry heat, -- but the
> > NaOH water solution certainly must lower the D-value more than
> > autoclaving alone.
> >
> > This has significance for extreme-ophile research and
> > Astromicrobiology theory.
> >
> > -- Davin
