Answer :Theres no real scientific measure of freshness, but if you mean vegetables that are closest in nutrient content to freshly picked vegetables, the best bet is probably frozen produce. Alice H. Lichtenstein, DSc, Stanley N. Gershoff professor of nutrition science and policy at Tufts Friedman School, says, For the most part, frozen vegetables are processed close to the point of harvesting, and, unless thawed and refrozen prior to sale, should retain most of their nutrients. Fresh vegetables -more so than frozen or canned- can vary in quality, depending on when they were picked relative to when they are available for purchase and the conditions under which they were stored, the length of time stored and the conditions under which they are displayed.
Canned vegetables are different. They are cooked and hence, not comparable to frozen or fresh vegetables. Canned vegetables are lower in heat-labile nutrients- those that are unstable when heated, as in the canning process. Many canned vegetables also have added salt; if you do opt for canned, make sure to look for those that are low in sodium. Of course, it is also important how the vegetables are stored and prepared once you get them home from the market: Minimize excessive heat and cooking fluid unless it is going to be consumed, such as in soups.