Fruits and vegetables that are flash-frozen at the farm are picked and preserved at their peak ripeness, when they have the most nutrients. At this point, freezing will keep the vitamins right where you want them.
Scientists from the University of Chester confirmed this idea with their study that measured nutrient levels in various produce that had been sitting in a fridge for three days, compared to frozen equivalents. They found more beneficial nutrients overall in the frozen samples, in everything from broccoli to blueberries. In fact, in two out of three cases, frozen fruits and veggies packed higher levels of antioxidants, including polyphenols, anthocyanins, lutein, and beta-carotene. In one report, the vitamin C content in fresh broccoli plummeted by more than 50 percent with a week, but dipped by just 10 percent over an entire year when frozen.