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Frog fresh milk

If your fridge is on the blink, why not toss a frog in your milk? Dr Karl explains this olden day foodie tip.

Refrigeration has been around for thousands of years. But before refrigeration, what would you do with a bucket of fresh milk on a hot day?

Well you could drink it really quickly, or you could turn it into cheese. But some farmers in Finland and Russia had another way to stop the milk from spoiling. They would drop a frog into a bucket of milk.

Not everyone dropped frogs into milk. Some people kept their milk drinkable in other ways — by using ice.

In days gone by, wealthy people in ancient Rome or ancient Greece would get a few tonnes of ice brought down from the mountains in late spring. They would then get it buried in a hole in the ground and cover it with a lot of sawdust. Voilà — instant refrigeration that would last them until winter.

In the early 19th century, ice boxes became popular. An ice box was just an insulated box a bit bigger than a large microwave oven. It was made out of wood, had metal walls made from tin or zinc, and some kind of insulation such as sawdust, straw or cork. Every day, the ice man would come down the street with his horse-drawn cart loaded with ice, and sell you a fresh chunk. That's how people kept food cold. The modern electrical refrigerator started becoming popular in the 1930s after the invention of the refrigerant gas, Freon.

But in small isolated rural villages in Russia and Finland it was freezing in winter, but really hot in summer — and they had no refrigeration of any kind. Ice boxes just weren't an option for them. They believed they could stop the milk from going sour by putting a frog into the milk container. This frog was the Russian brown frog, Rana temporalis.

What was going on? By itself, a bit of warmth won't turn the milk sour. But if you get some bacteria jumping into the milk, the warmth will encourage them to grow like crazy — making the milk sour.

Back in 2010, scientists from the United Arab Emirates University discovered that the skin of some frogs would release or ooze out chemicals that could fight both bacteria and fungi. They showed that these chemicals were peptides, which are small proteins — just a bunch of amino acids strung together. These frogs were native to a few African countries.

Since then, we've discovered that a chemical found in the mink frog of North America can vanquish the dreaded Iraqibacter. This is a drug-resistant bacterium that infected wounded American soldiers in Iraq.

And further, secretions from the skin of the foothill yellow-legged frog seem to be able to fight antibiotic-resistant MRSA Staphylococcus skin infection.

And in 2012, the organic chemist Dr Albert Lebedev, from Moscow State University, analysed chemicals on the skin of the Russian Brown Frog. They found some 76 different peptides, which (to refresh your memory) are just small proteins, or, a short string of amino acids.

About 27 of these peptides had significant antibacterial activity. They could kill both gram-positive Staphylococcus as well as gram-negative Salmonella — both of which can be quite nasty to humans. Mind you, this antibacterial activity was seen only on the laboratory bench, not in humans. But it could be related to why the milk didn't spoil, when you dropped the frog into the container.

And the scientists found some 49 peptides related to a very interesting peptide called "bradykinin". Bradykinin is a peptide made of nine amino acids strung together. Bradykinin is also associated with the dreaded anaphylactic reaction where your airways close down and your face swells up so you have difficulty in breathing, and your blood pressure drops. In some cases you can die from an anaphylactic reaction.

But getting back to dumping the Russian brown frog in your bucket of freshly produced warm milk, what about the problem of the frog urinating in the milk? Well, we drink water from dams, that fish live in, and that seems OK. So it stands to reason that a bit of frog wee is not going to make you croak...

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