Is kosher food blessed?
Some food that is blessed is also kosher. Some food that is kosher is also blessed. But there is nothing about being blessed that makes a food kosher, and nothing about being kosher that makes a food blessed.
Whether or not a food is kosher has to do with which animal it came from (beasts that have split hooves and chew their cud, fish that have fins and scales, birds that aren't carnivorous), how it's prepared (specific rules vis a vis slaughtering, draining blood, &c.) and with which other foods it's mixed (no meat and dairy together).
If a food does not meet the criteria, there is no amount of blessing that can change its status from not-kosher to kosher.
Short answer: Not really.
To be kosher food needs to come from certain sources and be certified to be in compliance with Jewish Law (Halacha). So while beef comes from a kosher animal, in order to be kosher it needs to be slaughtered in the prescribed manner, salted, and prepared in accordance with the rules of kosher.
Before you eat something, however, you are supposed to say a blessing. But the food would be just as kosher even if a blessing was not said.