Mainly focus and if you view at 200% you can see a white halo around the dark stems.
yes indeed there is a halo, but how to fix it?
It's not too hard to clone them out in photoshop or similar editing program, I clone out halos often. I find it easier with a pen tablet.
I'm going to be honest, even with the halos removed I'm not sure this photo would make it through though. I believe I'm seeing both natural daylight mixed with an interior incandescent light? I've never been successful at correcting white balance under these conditions and suspect the photo would need to be taken again using flash or without mixed lighting at the very least.
Focus needs to be fixed at the time you take the picture. There is no magic fix possible afterwards.
The halo is introduced by over processing (sharpening) the asset.
You also need to pay attention to the composition. If you only see the stem of the pepper, you should remove it. During the shoot, you should arrange the elements as needed.
All in all, you can't fix this picture.