Thomas' Plant-Related Blog

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Spices as antiseptics… maybe

with 8 comments

This post was chosen as an Editor's Selection for ResearchBlogging.org

For today, I’ve dug up a paper (I forget how) from 1998, when I was still in primary school, about why people like spicy foods, and why some cultures use more spice than others. The idea that we acquired a taste for spices to keep harmful bacteria in check isn’t implausible, but the evidence in the paper is more interesting than conclusive.

First off: does it work? Do spices have antibacterial properties? Yes, according to studies that the authors found. All the spices which had been tested were effective against some bacteria, and four (garlic, onion, allspice & oregano) had an effect on all the bacteria on which they were tested. Of course, publication bias might be hiding experiments where spices didn’t affect bacteria, but the researchers found studies for 30 of the 43 spices they were looking at.

Piles coloured spices on display

Spices on sale in Istanbul. Photo by echiner1 (flickr)

The ‘secondary compounds’ which give spices their various, powerful flavours, are probably part of the plants’ defences against pests and diseases, so it’s not a great surprise that they’d work against other bacteria.

The focus of the paper is the researchers’ rather epic study of traditional recipes. From 93 traditional recipe books, they read over 4500 meat-based recipes (meat is more likely to cause food poisoning) from 36 countries, noting the spices used in each. Most recipes included at least one spice, with onions and pepper the two most common overall. They match this up with the climate in each country, to find that hotter countries have more recipes with spices in, use more spices per recipe, and use the available spices more often. This, they say, is because bacteria will multiply quicker in warm countries, so more spices will be needed to keep them in check. On the other hand, they didn’t find any connection between spice use and rainfall.

It’s an interesting idea, but the statistics they use to check it aren’t great. It all hinges on whether each country can be treated as an independent case. They spend the best part of a page trying to justify this, but in the end seem to say “if we grouped some countries together, there wouldn’t be enough to do statistics with.” I sympathise, but I reckon it might be misleading to do statistical tests at all. There’s a particular problem at the cooler end of the temperature range, where almost all the countries are in Europe. If we share a common, relatively non-spicy cuisine, that could be making the correlation look stronger than it really is.

They also look more specifically at which spices are being used: for example, they reckon that hotter countries use more of the spices that are most effective against bacteria. But this, too, is a bit misleading. Even ‘traditional’ recipes can include relatively new foods; what could be more English than roast potatoes, from a plant we knew nothing of a few centuries ago? Chilli peppers are also from South America, so couldn’t have been used in Indian cuisine before Columbus. Many of the spices they look at have been spread around the world only in the last few centuries, presumably into cultures which had already developed tastes for more or less spicy food.

The patterns are interesting, and going through thousands of recipes must have taken a fair amount of work. But I don’t think the statistical analysis is enough to close the case. Perhaps an experimental approach would compliment it: how well do different combinations of spices delay bacteria growing on meat at different temperatures? And could humans hit upon this without knowing about bacteria, by associating non-spicy food with the nausea caused by food poisoning? The ethics committee might have something to say about testing the latter, but perhaps it could be done with rats.

Reference:

Billing, J., & Sherman, P. (1998). Antimicrobial Functions of Spices: Why Some Like it Hot The Quarterly Review of Biology, 73 (1), 3-49 DOI: 10.1086/420058

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Written by Thomas Kluyver

26 August, 2010 at 10:54 pm

Posted in Papers

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8 Responses

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  1. I concur completely that the general case for antibiotic activity in spices is weak, but I thought that each spice was then tested for antibiotic activity? Sorry, the reference escapes me at the moment. And other health related benefits of spices regularly get claimed like that for tumeric, a close relative of ginger.

    The Phytophactor

    27 August, 2010 at 9:38 pm

    • I’m hoping to have a look through the more recent literature on the topic. This paper cited quite a lot of studies apparently showing antibiotic activities in various spices or spice extracts, although I’ve not been and read any of those papers myself.

      Thomas Kluyver

      29 August, 2010 at 4:02 pm

  2. A few follow-up papers:
    – A detailed review of the antimicrobial effects of various spices (2004). It seems there’s quite a bit of evidence that various spices are effective against some bacteria and fungi.
    Animals can link what they eat with effects hours later, even to eat things that (presumably) taste bitter (2001). So the principle of humans acquiring a taste for spices to avoid subsequent nausea is sound.
    A somewhat pithier write-up of this study by the same authors (1999).

    Thomas Kluyver

    29 August, 2010 at 9:26 pm

  3. “And could humans hit upon this without knowing about bacteria, by associating non-spicy food with the nausea caused by food poisoning? ”

    Seems pretty reasonable. If I try out a new receipe and get really sick, I’m not likely to try it again, sure that goes for mist people. If spicy receipes in general leave fewer people sick, that might also allow these receipes to stay in use. Selection at work…

    On the other hand, I’d never recommend reasoning over experimental data, rats may help us solve the question…

    Hege F.

    30 August, 2010 at 6:56 pm

    • I guess it depends where else the sickness could come from. How clean was the stream you drank from this afternoon? Could you have caught a bug from your friend? I’m not an anthropologist, so I don’t know what people knew about disease centuries ago.

      For that matter, people may also see it as a divine or supernatural punishment. I guess that ties in to religious food laws, e.g. avoiding pork because of the potential parasites.

      Thomas Kluyver

      3 September, 2010 at 12:15 am

  4. Interesting :-)
    Given that the method / time of cooking for various foods will affect the probability of food poisoning, a parallel line of enquiry could look to see if there was any correlation between more thorough cooking styles and climate.

    ianafd

    31 August, 2010 at 5:00 pm

    • Interesting idea. I’ve read that cooking style is also linked with the technology available: where there are pottery vessels to cook food in, boiling and stewing are possible, while elsewhere roasting is the norm. No idea how they each affect bacteria, although I guess roasting (and later frying) can reach higher temperatures than boiling.

      Thomas Kluyver

      3 September, 2010 at 12:23 am

  5. […] Spices as antiseptics… maybe. Spices can add lots of "zing" to your food, and make some people suffer while eating it, but do they serve an even more important biological function? Thomas Kluyver at Thomas' Plant-Related Blog looks at the evidence that the use of spices has served an antiseptic purpose in food preparation, and the limitations of that evidence. […]


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