Milk used to be delivered to your doorstep in the morning and if it was left out of the fridge it was 'off' the next day.
Now we've got "Sell By" dates of up to 10 days (maybe more) so what's going in here ? Maybe it's just advances in hygiene . . ? Maybe there are some additives we're not in on ?
As for fruit & veg; I find things like pears are usually rock hard and under ripe from Tesco but within a week they are showing all the signs of the bruising they took during delivery/handling and are getting very soft and overripe.
I don't know about irradiation - lots of talk but do they have to tell you or not ?