Bob Atkins , May 24, 2012; 12:02 a.m.
Depends how big the food is....
Actually I doubt that a 50mm lens would be noticeably better than your current kit lens. The 50mm lenses are faster, but you probably aren't shooting in dim light and you'd probably need to stop down to get good depth of field. Since web images are small, the difference in the images between a prime and a zoom may not be noticeable.
To be honest, I don't see anything wrong with your current images. They look just fine to me.
If you want a fast 50 for other reasons too, then by all means get one. The 50/1.4 is slightly better, but it's quite a bit more expensive and the focus mechanism, which generally reliable, is more prone to failure than most. I find the 50/1.8 just fine for portrait work (though I prefer the 85/1.8).