[SOUND] So we see that 98% milk fat is triglycerides or [INAUDIBLE]. Three fatty acids again, you've got three carbons on the glycerol molecule, the fatty acids are attached to that. In those cases where there's only two of them, then that's called a diacylglycerol, two fatty acids. Or monoacylglycerol, there's only one fatty acid on the glycerol backbone. All of those are present in milk fat, but the bulk of it is actually triglyceride. Where do those fatty acids come from? There are two sources of fatty acids. One is called de novo synthesis. De novo synthesis means it's actually synthesized in the mammary epithelial cell, usually it's from various kinds of carbon sources. Whether it's glucose or acetate or something like that, they actually produce new fresh in the mammary epithelial cell. The other one is from the diet. So triglycerides that are in the diet, ingested, they're taken apart. Basically the glycerol and the fatty acids are taken apart in the intestine, absorbed. They're repackaged in the intestinal cells and to lipoproteins, kind of the microns for example. Those go around through the blood, they go to the mammary gland. They're taking apart again, the fatty acids and glycerol are absorbed by the mammary epithelia cell. Packaged back together, put back together and that's secreted as the milk fat. So again, diet can really impact what the composition of milk fat is in most species. Ruminants, not as much, but in most other species, it can certainly impact the composition of milk fat with what's actually being ingested by the lactating female. Once the triglycerides are produced, they are hydrophobic. So they kind of glomm together and if they actually form something called milk fat droplet. And then we'll see here in a moment that's actually secreted and once it's actually secreted. It's bound by the membrane of the apical site of the epithelial cell and once it's out in the milk, we call it the milk fat globule. So let's take a look at some globules here. This is a slide we shared before in one of the other videos and that is just some diluted whole milk. Put under a microscope, real thin layer and each one of these little specks here is a milk fat globule. So each one of these specks is a milk fat globule, very, very small. They're running at about, say most of them are going to be say between one and roughly eight micrometers in diameter. Some are smaller, some are a little bit larger, but most of them are going to be between one and eight micrometers. We'll go to the next slide. And again, this is one that we've seen in some other videos. So we have the KC micelles are the electron-dense things. The great big things are the milk fat globules and if you look carefully, a lot of them seem to have this darkish material around them. That's actually protein that wraps around or encapsulates this globule inside the cell. And then there's actually a membrane around there. It's kind of hard to see the membranes around that. Again, there would be a membrane around here, kind of hard to see in this image. This is the electron dense protein, here is a coating around that. So this milk fat globulin would be in the mammary epithelial cell. And coated by these milk fat globule associated membranes and then there's a membrane around that. So we can see how that works, let's go to the next side and this is a mammary epithelial cell, here's the nucleus, the cell goes from basically here to about there. The basal site is here. The lumen side is up here and right here is a milk fat globule. Milk fat droplet, because technically it's still inside the cell, just about ready to pinch off. So those things come up to the surface, they kind of push their way out, they're wrapped around by the membrane, that apical membrane. And so when they're actually secreted and floating around actually in the lumen of the alveolus in the milk, they're actually wrapped around by this membrane. And that's important because what we're going to do here in a moment is we're going to go make some butter. And the whole process of making butter is you disrupt the membrane. All that triglyceride, the fat comes together forming what we call butter. So we see that milk fat is secreted in these globules and they're bound by a membrane. And when we disrupt that membrane, what happens is all those triglycerides, those trisoglycerides start glomming together. And that's basically the way you make butter. It's the fundamental concept of making butter. So what I do, I have here two jars with some heavy whipping cream. Heavy whipping cream is about 30-35% milk fat, so a very, very high concentration of milk fat. And what we would do in this jar, just again, just milk, some heavy whipping cream. Is to really shake this really hard for a bit, it will take several minutes. I don't really want to take that long at the moment. So what I want to do is I've already done this one and so we've actually got a butter ball. So what we'll do is we'll dump these out, so you can kind of see what the difference is. This is one that is just heavy whipping cream This one is one that's been shaken, again, that action has disrupted or broken up the, There we go, broken up the membranes around those milk fat globules, they've kind of come together and given us the butter ball. So this is technically buttermilk here. Again, this is what we started with, so think of a churn, those kinds of things. That's really what you're doing is you're breaking up those membranes around the milk fat globules. And ultimately ending up with the butter.
