DEAR DR. BLONZ: I believe I heard, at some point in my schooling, that rinsing and draining canned vegetables reduces their sodium content as much as 25 to 30 percent. I have searched through everything I have (old textbooks, lecture notes, etc.) and cannot find a single reference. I can’t believe there isn’t something more recent than that! Do you know how much the sodium content is reduced when canned vegetables are rinsed? Are you aware of any research articles on this topic? -- L.K., Phoenix

DEAR L.K.: Salt, or sodium chloride, dissolves easily in water, so rinsing canned vegetables and beans will certainly reduce their sodium content. As for the exact formula or percent reduction for a particular food, it would depend on total sodium in the food, the amount of added salt and the volume of water exchanged.

There is no specific data that I am aware of that works for all products. But you should be assured that rinsing canned vegetables is an effective way to cut their sodium content -- perhaps as much as 40 percent in some cases. I hope this helps.

DEAR DR. BLONZ: I am a big fan of tomatoes, and understand they contain a healthy compound called lycopene. I know that cooked tomatoes contain more lycopene than raw, and it is recommended to consume cooked tomatoes (such as sauce with pasta or pizza). I also like sun-dried tomatoes. What is the comparable vitamin and mineral content of sun-dried versus fresh tomatoes? -- S.S., Sacramento, California

DEAR S.S.: Sun-drying reduces vitamin C and vitamin A, and, to a lesser degree, some of the other vitamins. But the mineral content will remain largely the same. As for the lycopene, it helps to understand that cooked tomatoes don’t contain any more lycopene than fresh. Rather, the lycopene is chemically bound inside the cell matrix of the fresh tomato plant, and the cooking process breaks the bond, thus making the lycopene more bioavailable (absorbed with greater efficiency). Given that lycopene is a fat-soluble substance, eating tomatoes with some fat can add to lycopene’s bioavailability.

Sun-drying isn’t the same as cooking, but from the standpoint of lycopene absorption, it’s probably better than having fresh. When the water is removed, the cells do shrink, and they can break, especially if heat is used during the drying process.

Go ahead and enjoy your sun-dried tomatoes, but be sure to give them a good chew. If the lycopene is what you’re after, eat them with -- or within an hour of -- a fat-containing meal or snack.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I drink decaffeinated coffee, but have been hearing about dangers from the methods used to remove the caffeine. Is organic decaf any safer? -- S.A., San Diego

DEAR S.A.: To make decaf coffee, you want to remove caffeine while leaving all other substances in place. This requires the use of a caffeine solvent and specialized methods. Solvents currently in use include water, methylene chloride, ethyl acetate, triglycerides or pressurized carbon dioxide.

One “indirect” method involves taking a load of green coffee beans and placing them in a quantity of water. All water-soluble substances, including caffeine, are drawn into the water. This solution is separated from the coffee beans, and that first batch of beans is discarded. The next step is a process that selectively removes the caffeine from the solution. This can be done using a different solvent that is subsequently eliminated, along with its caffeine, or by passing the caffeine-rich water extract through a specially treated charcoal filter that grabs only the caffeine. The latter process is referred to as the Swiss Water Process. What’s left is a working solution containing all water-soluble components, minus caffeine.

The next batch of green coffee beans gets put into the working solution. Only caffeine gets extracted, because an equilibrium exists between the concentration of the other water-soluble components in the beans and that which is present in the working solution. The decaffeinated second batch moves on to get roasted, and that second solution goes through its caffeine-extraction step to be used with subsequent batches.

A “direct” method involves mixing the selected caffeine solvent directly with the beans. Methylene chloride or ethyl acetate are the solvents most often used. After it has had a chance to dissolve the caffeine, the solvent is removed, with the caffeine in tow. The beans are gently steamed to eliminate any remaining solvent residue.

Methylene chloride is a carcinogen, but there shouldn’t be any left on the beans to pose a health risk. This is because methylene chloride evaporates around 110 degrees -- well below steaming temperature, and also well below the temperature at which coffee is brewed. Ethyl acetate is a compound that naturally occurs in fruits and vegetables, and is often used when decaffeinating tea leaves. In all the above, the green coffee beans (or tea leaves) are ready for drying, roasting or further processing after the caffeine is removed.

Other, more expensive methods utilize carbon dioxide that has been liquefied under high pressure. (This is a process approved for organic coffee and tea production.) The liquefied CO2 dissolves the caffeine from the tea leaves or coffee beans and is then drained off. Another method utilizes the fatty substances called triglycerides.

Whatever the method, decaffeination technology has improved greatly over the years, and flavor differences are often hard to detect. Much also depends on the quality of the beans and tea leaves, together with the particular practices of the roaster.

Note that the use of the term “water process” with decaffeinated beans doesn’t tell you the whole story, since most indirect methods utilize a water extraction somewhere along the way. If the label specifically states “Swiss Water Process” or has other additional information, a better determination can be made. There is more on this topic at tinyurl.com/gov9l88.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I have been eating vegetarian for over a year now, and I keep reading about compounds in vegetables that prevent minerals from being absorbed. I’m concerned, because my main sources of calcium are vegetables and grains. -- G.R., Portland, Oregon

DEAR G.R.: Some vegetables do contain compounds that bind, or “chelate” (KEY-late), minerals such as calcium, magnesium, iron and zinc, preventing their absorption. Two examples of these compounds are phytates, found in oatmeal and other whole grains, and oxalates, found in rhubarb and spinach (among other foods).

Spinach, for example, appears to be a good source of calcium and magnesium: A 100-gram (3 1/2-ounce) serving has 99 mg of calcium (10 percent of the Daily Value) and 79 mg of magnesium (20 percent of the Daily Value). However, by virtue of its oxalate content, spinach should not be considered a good dietary source of these minerals.

Usually, about 10 to 25 percent of the calcium in foods tends to be absorbed, but a study in the April 1988 American Journal of Clinical Nutrition reported that only about 5 percent of the calcium in spinach is actually absorbed. A second study two years later in the same journal reported that the calcium absorption in a low-oxalate vegetable, such as kale, was comparable to that of dairy products. It is important to appreciate that spinach is a wonderful food and a rich source of phytonutrients, aside from any impact of oxalates on the bioavailability of its minerals.

An interesting story along these lines relates to zinc deficiency, which was first described in men consuming a high-phytate cereal-grain diet. The phytates in whole grains are not a problem in yeast-leavened breads: Enzymes in yeast can break the bond between the phytate and the mineral, making the mineral bioavailable. With pita bread and similar items, however, which undergo a relatively short fermentation and baking, there isn’t sufficient time for the yeast enzyme to work its magic. As such, zinc deficiency tends to be more prevalent in parts of the Middle East where pita bread can account for as much as 85 percent of calories. Zinc deficiency has a number of effects, one of which is stunted growth if present during childhood. For more on zinc, see tinyurl.com/owql53a.

Seeing as vegetables and grains are the core of your diet, make sure you include a variety of different food sources. Fruit and vegetable sources of calcium without significant quantities of chelators include broccoli, turnip greens, collards, kale, mustard, figs and almonds.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.