最初の一口

first bite

Whatever it was, that first bite was important, right?

Whatever you eat, the first bite tastes delicious when you are hungry.

first mouthful

The first mouthful of anything tastes good when you're hungry. 

If you've been hungry for a while, anything tastes good when you first start eating.

mouthful   /'maƱθfƱl/　n)口いっぱい･一口