Years ago we used to have fresh milk delivered to our doorsteps every day. Whatever they do to it these days it seems to last at least a week, even in the plastic containers. It was always pasteurised (at least in my lifetime) so I'm guessing it's the homogenisation process that has extended the shelf life. Having said that, milk floats weren't refrigerated in the good old days and the bottles were clear glass so probably more susceptible to light and apart from the big supermarkets it wasn't generally refrigerated in shops, just stacked in plastic crates.