Thomas' Plant-Related Blog

On plant science. Mostly.

Posts Tagged ‘Using plants

Spices as antiseptics… maybe

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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.


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

Written by Thomas Kluyver

26 August, 2010 at 10:54 pm

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New crops: perennial grains?

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Most of our staple crops are annuals—plants that grow from seed, produce the next generation of seeds and then die, all in one year. In particular, the ‘big three’ crops, rice, wheat and maize, are all annuals. What would life be like if we instead grew perennials—plants that last more than one year? No more yearly ploughing and sowing.

Pear orchard

Pear orchard in the US. Photo by victorhansonsmith (flickr)

First things first: we’ve already got plenty of perennial crops. Many fruits, such as apples, grapes and kiwis, grow on trees and vines, and plants like the tomato can grow as annuals or perennials. But they’re luxuries, not our daily bread. The cereals and pulses that we depend on are almost all annuals. Read the rest of this entry »

Written by Thomas Kluyver

28 July, 2010 at 11:02 pm

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Photosynthesis in frog foam

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Although Brazil’s been making biofuels for decades, the rest of the world has quickly got interested over the last few years, due to concerns about climate change, as well as the rising price of oil. Unfortunately, it’s none too easy: plants tend to store a lot of the energy in molecules that are hard to break down, like cellulose. To make matters worse, the land needed to grow these plants is land that can’t be used to grow food, nor left to nature.

One option is to copy photosynthesis, and run the process without the plants. With a little help from a South American frog, it seems that might work. Some scientists in Ohio managed to assemble a set of enzymes to produce glucose from carbon dioxide and sunlight. Here’s what they used:

  • Tungara frogs and foam nest

    Túngara frogs with foam nest. Image by paulbradley (flickr)

    A surfactant protein, Rsn-2, from the Túngara frog, to make the foam. The frog itself uses the foam to protect its eggs. The experiments found that the system worked better using this foam than making foam with an artificial detergent, a testament to the power of evolution.

  • Bacteriorhodopsin (from Archaea) to capture light energy and pump protons.
  • An ATP synthase from a bacterium, which could use those protons to make ATP, the standard form of energy in a cell. This and the bacteriorhodopsin were embedded in lipid vesicles—little spheres made from a thin layer of fats enclosing some water, not unlike a soap bubble. The bacteriorhodopsin reduced the pH inside the vesicle, and that difference drove the ATP synthase.
  • The enzymes of the Calvin cycle, including RUBISCO, which collectively fix carbon dioxide and produce carbohydrates.
  • Several more enzymes, to convert the carbohydrates from the Calvin cycle into glucose, which we can easily use.

By my count, there are no fewer than four kingdoms of life contributing to this: an animal, an archaeon, a bacterium, and a plant (or several plants). The importance of the frog foam is to spread the enzymes out, so that light and carbon dioxide can easily get to them. I wonder, though, if they would use up the CO2 in the bubbles? Perhaps it could be continually reprocessed, the carbohydrates taken out, and the foam re-formed with new CO2.

The researchers validated that each step worked by itself, then plugged them all together to prove that the system really could make glucose from sunlight. They suggest that it could be used to produce a fuel called DMF, and calculate that, in ideal conditions, it could produce as much as 34.5 tonnes per hectare per year. They say that compares favourably to production from plants, although I can’t find any mention of DMF in the reference they give for comparison.

One possible application is on rooftops, where we don’t generally try to grow food. Since bacteriorhodopsin is purple, this raises the tantalising thought of one day covering my roof with a thick layer of purple foam, all in the name of the environment, but sadly I don’t think it will work quite like that. They also suggest that it could be used at sources of carbon dioxide, such as fossil fuel power plants.


Wendell, D., Todd, J., & Montemagno, C. (2010). Artificial Photosynthesis in Ranaspumin-2 Based Foam Nano Letters DOI: 10.1021/nl100550k
Press release

Written by Thomas Kluyver

29 March, 2010 at 9:40 pm

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Living bridges

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I couldn’t describe them better than Prof. Iain Stewart, on How Earth Made Us for the BBC:

More info on the bridges, made from Ficus elastica, a relative of the fig, can be found  on this tourism website.

He’s also visited a seed vault he doesn’t mention the name of, but it can only really be the one on Svalbard.

Written by Thomas Kluyver

27 January, 2010 at 6:55 pm

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