Why does meat spoil faster than plant matter?

  1. Simfish

    Simfish 827
    Gold Member

    Also - how did diseases like smallpox and pneumonia evolve? When the host dies, microorganisms responsible for those diseases lose their source of energy. So how does it benefit them (reproductively) to lower the "fitness" of the humans they afflict?
  2. jcsd
  3. jim mcnamara

    jim mcnamara 1,482
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    A lot of our diseases like cholera, smallpox, influenza and others ultimately derive from our association with domesticated animals: pigs, cows, ducks->pigs->humans, respectively.

    It was long known, for example, that milkmaids caught cowpox and once they had been exposed to cowpox, they no longer caught smallpox. Cattle are the ultimate source of smallpox in humans.
    As to why to diseases become less deadly, syphilis shows this trend over time. There was a syphilis pandemic during the 1500's. People who came down with primary symptoms usually died shortly thereafter from the secondary form of the disease. Now there are less virulent extant strains of syphilis that take far longer to show seconday symptoms - meaning that the most virulent strains have been selected against.

    See Hans Zinsser - 'Rats, Lice and History'
  4. Astronuc

    Staff: Mentor

  5. Evo

    Staff: Mentor

    I'm assuming you mean un-refrigerated meat? Because refrigerated meat can last much longer than some refrigerated vegetables. As a matter of fact, "aging" is what gives some meat like beef it's desirable flavor.

    Certain vegetables, like letuce, will turn slimy very quickly, even refrigerated. More hardy root vegetables, if kept in low humidity, will keep quite well for longer periods.

    Even un-refrigerated, techniques like salting and smoking will preserve meat because it prevents bacteria from growing.
  6. Spoilage is generally due to the growth and metabolism of microbes. The food becomes infected, the infecting microbes use the food, grow and produce end products that we generally find objectionable. The microbes themselves may also be capable of causing disease and some of these microbes can produce toxins into the food that can cause illness or death when consumed. Plant cell walls are robust and take some effort to degrade. Animal cells have no wall and a lot more protein, so they are easier to access and the nutrients are rapidly degraded and used. Animal cells self degrade a lot faster, making the nutrients even more readily available and accelerating the microbial activity.
  7. jim mcnamara

    jim mcnamara 1,482
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    Actually a species of soft-rot fungus attacking skinless fruit or a tuber causes damage as reapidly as does a microbe attacking meat. The main difference is that a lot of plants are kept with the "skin" on the item, nature's protection against microbes, not the case with meat.

    Because meat contains largely water, proteins, and fats, the breakdown products of meat decay smell awful - eg. things like hydrogen sulfide (rotten egg smell), rotten fish smell (trimetylamine) are emitted. Humans can smell these compounds in minute concentrations.

    Soft rots in plant materials may not produce foul stomach-turning smells, especially in high starvh content foods. They just look awful. As a result you can of remove what appears to be bad in plant material and still eat it. Meat becomes effused with the compounds I mentioned above. Before refrigeration, people resorted to using powerful smells/tastes to mask the rotted meat taste - things like vinegar, juniper berries.

    In other words, meat may sometimes become "gagful" long before plants do due to the nature of microbial byproducts. And the protective skins on the plant items.

    Prior to 1900 a major cause of death in the US was from spoiled and improperly handled foods. This was one of the major efforts of the USDA and later the FDA - foods safe from food-borne illnesses and spoilage. Salmonella, botulism, tyhoid fever, cholera: all can be passed from food preparer to food consumer very easily.
  8. Andy Resnick

    Andy Resnick 5,781
    Science Advisor

    All good responses. But won't sterile meat degrade due to cellular apoptosis and proteolysis? The cell walls of plants are much more rigid and can better withstand dehydration, for example.

    What's the deal with irradiated meat? I recall a flurry of news reports about how we can have meat stored at room temperature for extended epriods of time, but nothing ever came of it. And in Europe, isn't milk and yogurt kept unrefrigerated in the grocery stores?

    The points about disease lethality are well-taken as well. Ebola should be considered a failure since it kills the host so fast- no chance for it to replicate much. Cold comfort for the victims, I suppose. Diseases evolve very fast: witness what is going on regarding tuberculosis, which is 'enjoying' a resurgence, and many other antibiotic-resistant strains of bacteria lurking around hospitals. This is due to the shorter reproductive cycle of bacteria and viruses as compared to eukariotic (sp?) cells.

    I've long been curious how we maintain a huge bacterial load in our gut and on our skin without triggering an immune response.
  9. As far as I know, irradiated meat won't be on our shelves for some time in the future because of the negative perception of anything involving (ir)radiation. As for pasteurised milk and yoghurt on European supermarket shelves?; I have never come across this. The only unchilled milk available here is UHT which, if I remember correctly, is sterilised at about 115 deg C rather than pasteurised.
    The accelerated development of antibiotic resistance among pathogenic bacteria is nothing short of alarming. We coukd soon be looking at providing all treatment in home as hospitals become no go areas. We briefly fooled ourselves that we had conquered infection by pathogenic bacteria, but the evidence was already there back in the late 70s that the bugs were getting the better of us.
    The huge dose of microbes in our gut (I guess we have about 10 billion bugs per gram in there) do actually cause immune responses, but for the most part we have acclimatised to them and ideally the bugs in our systems are at worst commensal and at best beneficial. We see the immune response really coming into play when we accidentally consume some undesirable microbes that run riot in our intestines and promote all manner of unpleasant sypmptom, usually culminating in an evacuation of some sort. One of the reasons we are able to tolerate such a high number of bugs is that the gut acts like a continuous fermenter, constantly excreting microbes and their end products at one end as we feed them from the other. Otherwise the consequences would be catastrophic. And we also see bugs that live within this complex ecosystem get out of control every now and then, especially when we are immunosuppressed or have used antibiotics to accidentally wipe out many of the beneficial microbes that keep these guys under control. I guess a good example of this is the current situation with Clostridium difficile, where a relatively harmless resident of an otherwise healthy gut microflora gets an opportunity to proliferate and causes all manner of problems.

    There are a few significant contributors to our relative success in coping with diseases in the 20th century. Some (perhaps all) of these have already been mentioned but I thought I'd summarise them anyway. Separation of drinking water from sewage, treatment of drinking water, pasteurisation of milk, large scale vaccination against the infectious disease of childhood, the development of antibiotics, separation of cooked and raw food and an understanding of the mechanism by which food can be best preserved (including fermentation). Have I left something out?
  10. mgb_phys

    mgb_phys 8,952
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    Homework Helper

    Yes but thats a good thing!
    Go into the supermarket and you can pay double for special premium 21day aged beef, or pay half price for 1day before sell-by-date meat!

    It pretty much died out in europe because BSE was causing enough scares about beef that nobody wanted to add in the 'N' word. It has been used for some fruits that travel a long distance.

    Regular milk in the EU is refrigerated although it does last longer than in the USA.
    The limit for bacteria in milk in the EU is 400K cells/cc ( although most have a voluntary 200K/cc limit) in the USA it is 750K cells/cc. There is no real evidence that this level of bacteria is harmfull to healthy humans - but it does mean the milk spoils more quickly.

    Waterborne diseases can get away with killing you quickly because the new generations of pathogens can quickly get to other people. That's why many diseases (typhoid/cholera) cause diarrhoea and why they caused such dangerous epidemics.

    Bacteria on your skin aren't in contact with your immune system.
    Bacteria in your gut have had a long time to make friends with the immune system.
  11. Andy Resnick

    Andy Resnick 5,781
    Science Advisor

    Surely that's not the whole story- what prevents the bacteria (and mold, and yeast, and everything else in the air) from growing all over your skin? Why can't the bugs migrate down a hair follicle? Or rather, why doesn't this happen more often?

    What about newborns- how does the deveopment of the immune system coorperate with the introduction of gut bacteria?
  12. mgb_phys

    mgb_phys 8,952
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    A combination of there not being a lot of food - dead dry outer layers of skin aren't very nutritous. The skin sheds the outer layers continually, discarding the new invaders and anything that does land and try to grow is food for the little critters already living there.
    The oil secreted from pores and hair follicles mostly stops anything getting down them.

    Not sure - I imagine a combination of inheriting white blood cells from the mother and matching sets of bacteria through breast milk. I don't know if babies are born with gut fauna in place - hard to see how it would get there.
  13. Andy Resnick

    Andy Resnick 5,781
    Science Advisor

    That's just supposition- do you have any references?

    The gut epithelia are also continuously shed; yet the bacteria remain. There are situations where fungus will grow uncontrolled on skin- under nails and between toes- yet the growth is limited and slow. Lots of small bugs love to eat dead skin; it's not unreasonable to wonder why bacteria do not. There's lots of entrances into a body- ears, eyes, nails, in addition to sweat glands- yet somehow we do not go through life in a continuous state of inflammation.

    Babies get bacteria in the gut by eating. The first meal of a baby elephant (so I have been told) is the mother's feces. So the bacteria must first pass through the stomach (pH 1), the duodenum with all the digestive enzymes, and the small intestine before coming to rest in the large intestine, where they stay and grow. Not a pleasant trip!
  14. Moonbear

    Moonbear 12,266
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    I had always understood it to be due to the type of bacteria, not a difference in our immune response. The bacteria that thrive in our digestive tract without causing us trouble STAY in the digestive tract (or exit through the usual route) and are content to feed off the same foods we eat...some even are helpful in digesting parts of that food that animals can't (this is why cattle can digest fiber while we cannot do so very well...their bacteria do all the dirty work of breaking down cellulose). Nothing going through our digestive tract triggers an immune response because normally the immune system doesn't have access (we no more want the immune system attacking beneficial bacteria as that steak we just enjoyed). Those that make us ill attack the cells lining the digestive tract, thus penetrating INTO our cells and escaping the confines of the digestive tract, and that allows the immune cells access. (No references right now...I'll look later if I can verify this with references.)

    Another point left out above in all this discussion of meat vs plant spoilage, aging, drying, preservation, etc., is that temperature and humidity conditions are very important in determining whether meat (or plant material) will decompose or simply dehydrate. This is critical for things like aged beef as well as making dried sausages such as pepperoni or beef jerky, which once fully dried/cured can be stored for a long time at room temperature without spoilage. It's not unlike preserving pressed flowers by allowing them to dry rather than rot, while tossing the same plant matter into a compost heap with the right added humidity and warmth will rapidly decompose the plant material.
  15. Andy Resnick

    Andy Resnick 5,781
    Science Advisor

    There's more to the immune system than leukocytes and T-cells etc. There's also "mucosal immunity", or "systemic immunity" (I think they refer to the same phenomenon), and AFAIK, hardly anything is known about that immune response, which is much more primitive (i.e. occured earlier in evolution) than innate or adaptive immunity. In fact, the more I learn about the immune response, the less I understand. "innate", "adaptive", "mucosal".... ugh.


    Nice comments regarding humidity and meat degredation, BTW.
    Last edited: Apr 24, 2008
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