A quick Google search suggests that rancidification/peroxidation rates under LN2 storage are considered negligible for food storage purposes: LN2 is being investigated as an alternative to freezing for this very reason. LN2 also appears to slow down or stop rancidification in cryopreserved tissue (paper). Nevertheless, there are concerns about rancidification during the freeze/thaw process. Also, this does not give much info about the outcomes of long-term storage (decades and possibly centuries) as required in cryonics.
Hey, yeah, it did not occur to me till now, but I've recently kept butter in the freezer for about a year recently with no noticeable effect. I'm pretty sensitive to rancidity.
(1) Freezers vary dramatically -- a properly calibrated freezer should be below 0F. Many people have freezers that are warmer than this. Our freezer broke at one point, and our landlord was surprised to learn that freezers should be much below 0C (!)
(2) Butter can pick up funny smells in the freezer if it is not wrapped in strong plastic. This isn't technically rancidity, but it isn't pleasant. This depends on what else is stored in the freezer with it, of course, and how long it is stored.
I'm an biochemistry major, so organic chemistry takes up a large part of my time. I'm still just a lowly undergrad, though, so Google will probably do as well as me. In any case, here are my thoughts:
Rancidity is caused by several mechanisms: mostly hydrolysis, various microorganisms about which I know nothing, and oxidation. I do not think butter will go rancid in liquid nitrogen, since it would need water, microorganisms, or oxygen to do so. I imagine rancidification is slowed at cryogenic temperatures, but I'm not sure if oxidation and hydrolysis would completely stop.
I don't see why they wouldn't be... but given the site we're on, I'm hesitant to come right out and say yes.
I would suspect this question is not answerable with any precision at this time.
The presence of oxygen is certainly relevant to randification normally, so I would guess so; but don't quote me on it.
Are these or similar reactions possible in the brain, given all the cell membranes and mylenation and so on that are primarily made out of fat?
I don't see why they wouldn't be... but given the site we're on, I'm hesitant to come right out and say yes.
You shouldn't (be hesitant), not for that reason.
Heh, a good point; I would actually have replied the same way on any forum, but I thought I'd include that comment as a nod to LessWrong's devotion to rationality. It probably helped that I had just read an article about knowing when not to venture a guess!
I can't answer your specific question about rancidity, but it's no secret that the whole process causes pretty severe molecular damage, so either way you'll be counting on future science's ability to reconstruct you with less-than-perfect information.
- The boiling point of oxygen is about 90 kelvin (13 degrees higher than nitrogen's boiling point). If the liquid around a cryo-patient is not changed over time then we might expect the ratio of liquid oxygen to liquid nitrogen to increase over time. Is the presence of the liquid oxygen relevant to rancidty issues or not?
At the temperature of liquid oxygen, most bimolecular chemical reactions are largely inhibited. The rates of these reactions, in general, decrease rapidly with decreasing temperature. At very low temperatures the rates become too small to be measured, and for practical purposes it may be said that reaction ceases. This is especially true of oxidations, since, for example, neither sodium nor phosphorus immersed in liquid oxygen undergoes any apparent oxidation.
Based on my even more limited high school chem knowledge, I would say that oxygen turning into a liquid would speed up the process (faster than it would have occurred at 77 Kelvin), as things dissolve in liquids more readily than gases. So, if oxygen is in the rate law for fats turning rancid, this would increase the rate that it happens at.
Of course, there's a very good chance that due to the dependence on microbes this reaction wouldn't occur at all.
Microbial interaction is only responsible for some instances/types of rancidification. Oxidation and hydrolysis reactions can occur without microbes, although again the question becomes one of how quickly these reactions would occur at cryogenic temperatures (very slowly, but we are looking at potentially very long timespans here) and availability of species.
One elementary point I have not seen made yet is that a superintelligence can probably extract information from a rancid brain as easily as a non-rancid one although before the arrival of the superintelligence, it might be more likely for certain kinds of damage to happen to a rancid brain. Like others, I almost did not participate in this thread because someone who really knows the subject matter could probably give a vastly more definitive and credible answer.
I broached the subject of cryonics with a family member today. He offered almost none of the normal objections and I've been happy all day about the way the conversation went. One interesting issue that he raised that I'd like to find an answer for is the question in the title.
Butter goes rancid after a while at room temperature. It also goes rancid in the fridge and can absorb the other flavors if things aren't well contained inside the refrigerator. Butter also goes rancid if left in a normal freezer, which mostly is designed to bring things very close to the melting point of water around 273 kelvin.
This suggests that lipid chemistry responds to temperatures in a different way than intuitions mostly educated by other examples of freezing, which is relevant because the brain is mostly made out of fat, with some complicating proteins mixed in. My guess is that developing a "rancid brain" isn't likely to be a serious issue when you get down to the 77 kelvin of liquid nitrogen, but its still something I'd like to be able to answer directly and honestly, after really thinking about it in terms of "safety engineering".
One way to answer the direct question about butter might be to just perform the basic experiment with some butter samples at different temperatures (room, fridge, freezer, -80C freezer in a bio lab) and figure out how long butter stored each way takes to go rancid and then do some curve fitting, but that seems like it would take months or maybe even years, and butter doesn't even necessarily answer neurological questions directly. Even if I learned about butter chemistry, there could be open questions about brain chemistry. I've tentatively googled around for 30 minutes but organic chemistry isn't a primary area of expertise and I wasn't sure out to dig up the specialist scientific literature that might answer my question.
This community seemed like a good place to get help on the subject!
Here are some specific questions I'd love to know the answers to...
1. What are the precise chemical reactions are that are collectively referred to as rancidity in english, and how to they change at cryogenic temperatures? Does butter stop going rancid in liquid nitrogen?
2. Are these or similar reactions possible in the brain, given all the cell membranes and mylenation and so on that are primarily made out of fat?
3. How much personality/memory/mind relevant information might be lost to rancidity, if it happened? If there are brain or neuronal structures that are more likely to go rancid first, would the chemical changes involved in rancidity be likely to change our estimation of the structures "historical operation" or not?
4. The boiling point of oxygen is about 90 kelvin (13 degrees higher than nitrogen's boiling point). If the liquid around a cryo-patient is not changed over time then we might expect the ratio of liquid oxygen to liquid nitrogen to increase over time. Is the presence of the liquid oxygen relevant to rancidty issues or not?