Some times you gotta be fresh…and other times, frozen may be fresher than fresh. Some studies have shown that frozen fruits and vegetables can contain higher levels of vitamins and antioxidants compared to the fresh varieties from stores or farmers markets.
This is due to the fact that many frozen fruits and vegetables are processed and frozen right at the source, from minutes to hours after being picked or harvested during their peak ripeness. On the other hand, fresh produce maybe be held for days, weeks, or even months before being sold to consumers, then held at the home for even more time before being used. When these products are held at ambient temperatures or even refrigerated, they slowly and naturally lose some of their healthy properties over time. When product is frozen, it inhibits the loss of these volatile compounds, and provides more health benefits. Some fresh produce is also picked before being fully ripened to handle the delay in consumption, which reduces the overall health advantages even more.
Supermarkets and even farmers markets have a list of ways to make their foods look fresh, such as water misting and trimming. While these practices are normal, the overall health profile of these foods can often time be less than the frozen counterparts. There are even instances that refrigeration will INCREASE degradation of healthy compounds in certain food items, specifically soft fruits. It is still recommended that foods picked right from the ground are the best, but frozen can be just as good of an option.
And as a side note, if you do want to cook your fruits and vegetables while keeping the most nutritional value in the products, steaming is the optimal way to insure the least about of benefit loss. This is of course second to eating them raw.