However, this study actually tried to simulate various types of institutional cooking methods, whether food is being prepared to serve to large numbers of hospital patients at one time or to be held on a buffet table for a large crowd. Vegetables chosen were cut green beans or the brassica vegetable called swede rods or rutabaga (this study was conducted in Norway where rutabaga is a more commonly consumed vegetable).
(Photo: Rutabagas, photo from Wikipedia)
In the present study, vegetables were industrially blanched/frozen and then cooked in water or by pouch technology (boil-in-bag) with comparisons of their ability to retain vitamin C, total phenolics and antioxidative activity (DPPH and FRAP).
RESULTS: After conventional cooking, 50.4% total ascorbic acid, 76.7% total phenolics, 55.7% DPPH and 59.0% FRAP were recovered in the drained beans. After boil-in-bag cooking, significantly (P < 0.05) higher recoveries were obtained, i.e. 80.5% total ascorbic acid, 89.2% total phenolics, 94.8% DPPH and 92.9% FRAP. By conventional cooking, 13.5-42.8% of the nutrients leaked into the cooking water; while no leakage occurred by boil-in-bag cooking. Warm-holding beans after cooking reduced recoveries in all components. Recoveries in swede rods were comparable but overall slightly lower.
CONCLUSION: Industrially blanched/frozen vegetables should preferably be cooked by pouch technology, rather than conventional cooking in water. Including cooking water or exuded liquid into the final dish will increase the level of nutrients in a meal. Warm-holding of vegetables after cooking should be avoided.
Take home points:(1) If you purchase frozen vegetables (or freeze at home), look for bags that let you simply "boil in the bag" to prepare for serving.
(2) Use any liquid from cooking vegetables (in soup broth, cooking rice, add to your simmering pasta sauce, or just drink it like my mother has always done!)
(3) Serve vegetables hot, right away. Be at the front of the line at a buffet table or wait at a cafeteria line for a freshly prepared pan of vegetables. Ask if they were prepared in a pouch or water.
(4) I save all left-over liquid from preparing vegetables (even a few tablespoons) by placing into a container I keep in the freezer. When full, I have a quart of delicious vegetable soup stock filled with nutrients ready to thaw and use.
My husband would actually say that rutabagas are his favorite vegetable. He got an urgent phone call 30 years ago from my older son's daycare where they did not know what my son had brought as his contribution for that day's activity, making "stone soup"; yes, it was a rutabaga. My husband is also picky about pasties; only those that contain rutabagas and enough of them to actually taste "cut the mustard" for him. You can enjoy his delicious recipe (yes!) for Glazed Rutabagas right on this blog.
Where kale (and other Brassicas, like rutabaga) are more than decoration on my plate!
Diana Dyer, MS, RD