This time we were looking at small angle X-ray scattering of milk. Yes, you heard that right. Milk - the stuff that comes from a cow (or any mammal for that matter), the stuff you put on your breakfast cereal, the stuff cheese and ice cream and yoghurt are made of.
Milk is an amazing material. It enables minerals - particularly calcium - to be delivered to the body in a water-soluble (or at least, colloidal) form. Milk gets its white colour from casein micelles. These are basically clumps of protein, and inside those clumps are tiny crystals of calcium phosphate. If it wasn't for the casein proteins surrounding them, the crystals would basically precipitate out and not dissolve.
It turns out you can do lots of stuff to milk to change it. You can try some of these yourself. Take some milk, and add vinegar to it. You'll see it separate into white solid - that's the curd, made of casein proteins - and yellow-clear liquid, the whey. This is the first step in making cottage cheese. Vinegar is acidic, and it dissolves the calcium phosphate, which leads to the break-up of the casein micelles, which then join together into even bigger clumps that are visible to the naked eye.
We tried a number of things. Firstly we tried replacing some of the calcium with iron. Then, we tried adding an acidifying agent to simulate what happens when making yoghurt or cheese. Next, we did an in vitro digestion experiment. This basically entails setting up a beaker of milk, then adding gastric juices (you can buy these from a chemical supplier). Finally we ran an experiment on some milk and some cheese to see what happens as they are heated up.
This was all pretty ambitious - and even more so given the fact that our time was cut short quite significantly: we were meant to start at 8 am, but didn't get going until 3 pm because a piece of equipment we needed was broken by the previous users (although it wasn't their fault). So we had to come up with a different way of measuring those particular samples, which wasn't a problem. We were told we could have a couple of hours extra the following morning to finish things off if we needed it - which we did.
This setback meant we were running the in vitro digestion experiments from 3-9 am or thereabouts - not a good time to be working with syringes and needles and tiny glass capillaries, but we made it. We finished at about 10:30, by which time I was starting to get quite grumpy (the 'second wind' of sleep deprivation was wearing off in a big hurry), back to our accommodation and into bed, a total of 28 hrs of being awake non-stop. I think the most I've ever done in a continuous stretch is 32 hrs, but still, it's not easy. The day after basically didn't exist; we slept, then cleaned up in the lab, went for dinner, and slept again. The following day we drove out of town a bit to look for some kangaroos (which we saw - sorry I don't have pics, but you all know what a kangaroo looks like) then headed off to the airport.
Anyway the whole trip was really productive - now we just have to analyse the results and make sense of it. Some of the experiments we were able to see big changes, which is great, but it's going to be a team effort to understand what it all means.
And I've found that since I got back, I've really developed a new respect for milk.
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