I don't think so, 'molestar/criticar a' is another translation of 'pick at', where it means to bother each other/fight/quarrel. e.g. the children picked at each other all evening. http://idioms.thefreedictionary.com/pick+at If you pick at your food, you eat only a small amount of it. I'm not sure how you translate that to Spanish but I wouldn't have thought using 'molestar' was right, as it doesn't have anything to do with being bothered or upset by the food. I'm sad so I pick at my food. When we read that, we infer that because the person is sad they have lost their appetite. Therefore they only eat a small amount of the food on their plate, and 'go through the motions' of eating.

as Paul answered, there is no direct translation but, "picotear" is used for eating small portions, a verbalisation I believe comes from the word "pico" ( bird's "beak" ) as a bird eat very little at a time. It is used mostly in spanish for a sustitude for for "appetiser" but i think you can use it : "picoté la comida por que estaba triste"