Artifact #1: (How suspect are packaged greens?)
The stuff bought whole and chopped on the kitchen counter is definitely more healthful.
This is because time, temperature and damage during harvest and packing can deplete vitamins and other nutrients. Vegetables begin to shed them the second they’re picked.
Artifact #2: (Michael Pollen answers reader’s questions)
Frozen vegetables and fruits are a terrific and economical option when fresh is unavailable or too expensive. The nutritional quality is just as good — and sometimes even better, because the produce is often picked and frozen at its peak of quality. The only rap is that freezing collapses the cell walls of certain fruits and vegetables, at some cost to their crunch. But this has no bearing on nutrition.