DEAR DR. BLONZ: Both of the organic half-and-half products at my store are ultra-pasteurized, while the standard brands (not organic) are just pasteurized. What is the difference? -- J.J., Santa Fe, Ariz.

DEAR J.J.: Pasteurization and ultra-pasteurization are both heat treatments designed to reduce -- but not eliminate -- the presence of potentially harmful microorganisms. The two differ in the amount and duration of heat used. Pasteurization heats a dairy product to 160 degrees Fahrenheit for 15 seconds, while ultra-pasteurization heats the product up to 280 degrees Fahrenheit for up to 3 seconds. The higher heat used in ultra-pasteurization eliminates more bacteria, and results in a more shelf-stable product. Once opened, however, both types of products require refrigeration. Ultra-pasteurization is not widely used because the high heat can affect flavor. The process is usually used on products such as half-and-half or whipping cream, but ultra-pasteurized milk can be found in remote areas, or in stores that don't sell a high volume of milk.

DEAR DR. BLONZ: I have been enjoying dried apricots with breakfast, cutting them up to have with my cereal. It was pointed out that the ones I typically use are soft because they have added sulfur dioxide, and that this is something bad. Is this something I need to avoid? The ones without the sulfur dioxide are dry, leathery and difficult to cut. What is sulfur dioxide, and what purpose does it serve? What other products contain it? -- C.R. Waukesha, Wisc.

DEAR C.R.: Sulfur dioxide belongs to the group of preservatives known as the sulfites. Other sulfite preservatives include sodium sulfite, potassium sulfite, sodium metabisulfite and potassium metabisulfite. All can be used to help keep fruits and vegetables looking fresh. They can prevent discoloration as well as the growth of unwanted bacteria, molds and yeasts. Sulfur compounds are also used to help sanitize containers that are used in fermented beverages.

Sulfites are routinely used in wines and in dried fruits such as apricots, raisins, dates and figs for their antimicrobial effects, which allow for a longer shelf life. Bacteria and molds need small amounts of water to grow, so, as you noticed, apricots without sulfites (or some similar preservative) need to be dried down to that leatherlike consistency to achieve a comparable shelf life.

Sulfites are not without negatives. Some individuals experience adverse reactions to these preservatives, with symptoms ranging from headache, hives and mild shortness of breath up to a rare life-threatening breathing difficulty. The FDA estimates that about 1 percent of the general public can react in some way, and as high as 5 percent of those with asthma. The FDA has banned the use of sulfites on fresh fruits and vegetables (except potatoes) and it has to be indicated on the label whenever a sulfite preservative is present. You have been enjoying your sulfite-preserved dried apricots, so this would not appear to be an issue for you.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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: What is the propellant used in the nonstick cooking sprays, and how do the sprays work? Why are they more effective than merely spreading oil on the pan? I rely on these sprays when I stir-fry vegetables or when I roast a chicken. Is this practice as healthy as it's made out to be? -- S.T., New Orleans

DEAR S.T.: Nonstick cooking sprays contain a vegetable oil -- such as corn, soy, canola or olive oil -- plus lecithin, an ingredient from soybeans traditionally used to keep oil and water in solution together. Aerosol versions also contain a propellant gas. Although each uses oil, cooking sprays differ in their ability to form a thin, well-disbursed oil-lecithin film that stays between the cooking surface and the food. Some products also include very small amounts of a silicone compound and alcohol to prevent foaming and to facilitate the formation of the nonstick film.

Because the sprays use a minimum amount of oil, little fat is contributed to the meal. A one-second application -- an amount sufficient to cover a 10-inch skillet -- will contain less than one gram of fat. The Nutrition Facts label on many of these products have a "recommended serving" of a third of a second or less. Tough to pull off, but it does allow the manufacturer to claim the product supplies less than a half of a gram of fat per serving, which in turn allows the product to be labeled as "fat-free."

The ingredients should be clearly stated on the container so you can opt for a product that contains no more than the basic components. About the only safety issue would come from the fact that aerosol sprays require a compressed gas for a propellant. Some make use of hydrocarbons such as propane or isobutane, both of which can be highly flammable. Such sprays should only be used on cold surfaces and kept away from all flames. If a flammable hydrocarbon gas is used, there should be an appropriate warning label to this effect. You may be able to find a product that does not rely on flammable hydrocarbon gas propellants.

When using these sprays, shake well, as the ingredients need to be thoroughly mixed to work properly. An oft-ignored drawback from the use of these products is the waste contributed by the empty aerosol can. There are refillable pump sprays that limit this aspect, but the high pressure of the aerosol is what helps facilitate spray performance. If you go the homemade pump-spray route, you may have to experiment with oils, staying away from unfiltered oils with particulate matter that might clog the nozzle.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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 a math issue regarding body weight and body fat. If a pound contains 454 grams, and there are nine calories per gram of fat, please explain how a pound of body fat is said to contain only 3,500 calories. You and many others use this figure but the math does not add up. -- D.L., Poway, Calif.

DEAR D.L.: There are indeed 454 grams in a pound, as you point out. So how do we come up with 3,500 calories from a pound of body fat when 454 x 9 = 4,086 calories? To start with, consider that fat is our most calorie-dense substance and it is capable of providing an energy equivalent to nine calories per gram. It is utilized as the primary form of energy storage because humans, like other animals, need to be mobile. Imagine the image of a human with energy stores in the form of carbohydrate or even protein; if such were the case our bodies would need to take up over twice the space they do now.

Getting back to the math problem, the answer rests with the fact that adipose tissue in the body is not 100 percent pure fat. This tissue contains a small amount of water and some structural material, accounting for close to 15 percent of tissue weight. It is this nonfat portion that helps explain why a pound of body fat is said to contain approximately 3,500 calories worth of stored energy.

DEAR DR. BLONZ: I was wondering what your thoughts were regarding the use of sports drinks as a beverage for active children. -- E.F., Oakland, Calif.

DEAR E.F.: I would not consider a sport drink to be a universal go-to beverage for children; water fits that description. Next might be a nutrient-rich 100 percent fruit juice, ideally one from any of a variety of berries. Sports drinks can be helpful for those involved with hour-plus workouts or athletic events, in that they can help replace the sodium and potassium lost through perspiration. A small amount of sweetener helps make the drink more palatable, and it provides a small boost of the type of fuel that is in short supply during an extended workout. You don't want too much sugar as that can work at cross purposes by slowing absorption. I also advise against giving exercising children any drinks that contain stimulants, such as caffeine.

The journal Pediatrics found that an effective beverage contained, per 8-ounce serving, 14 grams of sugar (6 percent carbohydrate) and 110 milligrams of sodium (18 mmol/l sodium). See tinyurl.com/h9nne for more information. This is the same formula found in Gatorade and some other sport drinks. Check the Nutrition Facts label on any products before you buy.

I recommend that you make your own sports drink from fresh juices. Such a beverage provides the same nutrients as store-bought sports drinks, but contains genuine flavors and the added benefits of the fruit's phytochemicals. My recipe can be found at tinyurl.com/krkj8mx. You know your child best, so you should adjust the recipe accordingly.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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.