Q: What does an ORAC number mean on a food label? I've also seen it on some supplements. Is it a new nutrient? How much should we be eating of it?
A: ORAC is one of several methods used to measure antioxidant amounts. It stands for oxygen radical absorbance capacity, or the amount of free radicals (oxidants) that the food or the antioxidant being measured can neutralize. There are others with similar acronyms — TEAC, TOSC, FRAP, TRAP and more. They each use slightly different methods, and may measure different antioxidants, but ORAC has become the most popular and most commonly known. That's the easy part of your answer.
The short answer to the rest of your question is that no one knows how much is enough, or good or bad. Antioxidants are good, until we get too much of them. Then some of them, at least, seem to become bad.
There are dozens if not hundreds of antioxidants. Some have been tested in Petri dishes or on lab rats. But they don't translate well from a Petri dish to a dinner plate. They may not, and probably do not, work the same in people as in test tubes or lab animals. How well they survive the stomach, move around in the blood, get to our different organs or into our cells is not known. The same ORAC number for different fruits may be measuring different antioxidants in each one. And each may function differently in our bodies. Even comparing ORAC numbers on cartons or packages really tells you very little.
A big ORAC in one food might increase the antioxidant level in your blood while the same number in a different food or supplement does nothing. And a high blood level might not mean any difference in your health. Don't let big ORAC numbers sway your choices when buying foods or supplements, because they really don't mean anything yet. Eat a healthy, balanced diet with lots of colors and you'll be in good shape.
Q: Which is better nutritionally, buying dry beans and cooking them, or getting canned beans?
A: A big part of the difference depends on how you handle the canned beans, especially if you rinse them or not. Most beans are canned with added salt for flavor, so their sodium content is very high. Rinsing them will remove as much as a third to half of the sodium, but not all of it. So cooking your own from dry will be preferable in that sense.
Rinsing canned beans also removes some of the soluble fiber. That's what makes the liquid in the can thick, but it also is what helps our digestion, and it may help keep our cholesterol levels lower. There will be some B vitamins and minerals in that liquid as well, because the beans have been sitting and soaking in it since they were canned.
You will get less potassium, magnesium, iron and zinc from rinsed, canned beans than if you cooked the beans and used the cooking liquid in the dish you made. Some thiamine, riboflavin and niacin also will be lost by rinsing. On the other hand, rinsing canned beans also will remove some of the sugars that cause gas problems for many people. The protein content will not be affected by rinsing. It's about 15 grams per half cup. These differences are not huge.
Canned beans are very nutritious, high in fiber and minerals, and definitely a good addition to a diet. If you don't have time to soak and cook dry beans, by all means use canned ones. When possible use the liquid from the cans, but don't worry if you prefer to rinse them.