Frozen foods may actually retain more of their original nutrients than your fresh produce. When foods are frozen, its mineral content is retained, because freezing causes bacterial reproduction to stop and enzymatic reactions to slow.
Fresh foods may lose nutrients during shipping or while sitting in the grocery store. Also, unlike frozen foods, fresh produce is usually harvested unripe, so it does not develop all of its potential nutrients.
*When buying frozen fruit, buy uncut fruit - they retain more Vitamin C.
*Refreezing is safe, but causes a substantial loss of nutrients.