DEAR DR. BLONZ: A tomato carton at a local produce market stated that the tomatoes contained a number of "non-tomato ingredients." It listed petrolatum, paraffin, carnauba wax and food-grade mineral oil. The carton also stated that the fruit had been treated with ortho-phenylphenol to inhibit mold. Are these substances in or on the tomatoes, and are they dangerous to eat? -- P.P., Vallejo, California

DEAR P.P.: Petrolatum, paraffin and carnauba are different types of waxes. Produce growers apply waxes to their fruits and vegetables to retain moisture, slow flavor loss, enhance appearance and prevent mold during packing, shipping and selling. Petrolatum and paraffin are byproducts of petroleum (oil). Carnauba, which comes from the wax palm of Brazil, is also used in car wax.

Waxes are applied to a wide variety of produce, including tomatoes, apples, bell peppers, avocados, cucumbers, sweet potatoes, citrus fruits, peaches, pumpkins, eggplants, squash and hardshell nuts. Waxes are only used in small amounts, and are not considered harmful. Experts estimate that one pound of wax will cover 160,000 pieces of produce.

One potential cause for concern with waxes stems from the possible presence of pesticide and fumigant residues on the surface of the produce before the wax is applied. (In some cases, the pesticide or fumigant is mixed with the wax.) Ortho-phenylphenol is a type of anti-mold fumigant that's often used this way.

Chemicals cannot be washed off if embedded in a wax, but the health risk posed by the presence of such wax-bound pesticides or fumigant residues should be minimal if the chemicals are applied according to regulations. And, of course, it's only an issue for produce in which the skin is consumed.

Although you can try scrubbing these waxes off, it takes more than water to do the trick. A mild detergent, or products that claim to clean the wax off of produce (available at natural food stores) may be helpful. Without these, the only real way to "de-wax" the produce is to take off the peel.

It is important to understand that both conventional and organic growers can apply waxes as a protectant before shipping. All waxed produce should be labeled as such. Organic growers' waxes come from natural sources and do not contain any synthetic pesticides or fungicides. The presence of waxes is yet another reason why it's always best to consume a variety of fruits and vegetables, and change your selection with the seasons, rather than eating the same foods all the time.

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: Is there any nutritional advantage to goat's milk over cow's milk? What about those who are allergic to cow's milk, or who are lactose-intolerant? -- T.R., La Jolla, California

DEAR T.R.: All things considered, it is a bit of a wash. Goat's milk has a bit more protein, fat, potassium, calcium and magnesium than cow's milk, and even a small amount of vitamin C. But there is less vitamin B12, folate, selenium and riboflavin.

There are differences in taste, but most people are able to digest cow's milk and goat's milk with equal ease. A few may find the softer curd of goat's milk easier on the stomach. Both milks have comparable levels of lactose, but because they are from different animals, their proteins will not be identical.

If you are thinking of trying goat's milk because you're allergic to cow's milk, start with a small amount. There have been cases, especially in young children, of cross-reactions among different types of milk. In other words, a child with an allergy to cow's milk may also react to goat's milk, even without any previous exposure to it.

DEAR DR. BLONZ: When you fry or scramble your eggs, do you destroy more protein than if you were to poach them? I have heard this and wonder if it is true. Also, what goes on during the cooking of the egg white? -- G.G., Berkeley, California

DEAR G.G.: Bottom line first: As long as you do not overcook your eggs, there is no evidence that frying or scrambling will destroy significantly more protein than poaching.

As for egg whites: They are a great source of high-quality protein. Think of individual protein molecules as long chains of amino acids; when viewed three-dimensionally, those in an egg are folded among themselves like crumpled strips of paper. Raw egg white is almost 90 percent water by weight, and the proteins are suspended in the clear, viscous liquid.

When heated, protein globules tend to uncoil a bit. This step helps our digestive process, as it makes it easier for our protein-digesting enzymes to get at the protein and break it into individual amino acids -- a necessary step prior to absorption. Heated egg proteins begin to interconnect, and when this happens, the egg white becomes solid and opaque. Water remains at first, but as more and more heat is applied, the water eventually gets squeezed out and the egg white takes on a harder, eventually rubbery, texture.

The idea, of course, is to cook the egg without overdoing it. Poaching takes place at or below 212 degrees F, the boiling point of water. Frying takes place at higher temperatures: at or slightly above 250 degrees F. Excessive heat from overcooking can destroy any protein. It makes sense that there would be a greater risk of overdoing it with frying or scrambling than with poaching, but the temperatures at which eggs are normally prepared would not be high enough to cause any significant protein destruction.

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: There was a great deal of publicity about mad cow disease a few years ago, including some distressing videos of suffering cattle and several tragic human deaths. We were advised to cook any beef products very thoroughly, or better yet, to avoid beef altogether. Then the matter dropped off the media world. What became of this topic, and do we still need to overcook all beef? What about products such as gelatin? -- P/RL, Berkeley, California

Dear P/RL: It is good that we haven't heard that much lately about bovine spongiform encephalopathy (BSE), also known as mad cow disease, as it is reflective of good science and effective controls. In people, the disease caused by BSE is a variant of Creutzfeldt-Jakob disease (vCJD), and it is a progressive, ultimately fatal condition that affects the brain and nervous system. Both BSE and vCJD are caused by an abnormal protein, referred to as a "prion," acting as an infectious agent. The term "prion" was coined by University of California San Francisco scientist Stanley Prusiner, who discovered this protein as an infectious entity and won the Nobel Prize for his efforts.

Your comment about cooking is misplaced given that high-heat exposures from cooking, boiling or even microwaving cannot reliably destroy the infectious nature of prions. While they are not airborne and not transmitted by casual contact, prions can be transmitted by contact with infectious bodily fluids or tissues, or the consumption of BSE-contaminated cattle products. The outbreak was first discovered in the United Kingdom in the 1990s, and once the source of the disease was uncovered, it led to the isolation and destruction of thousands of suspect cattle and the institution of rigid control measures.

Worldwide, 95 percent of cases have occurred in the United Kingdom. There continue to be strict import restrictions to prevent BSE-positive cattle from entering the United States. A history of the epidemic in the United Kingdom can be found at tinyurl.com/n9f7u6k. There is also information at the U.S. Centers for Disease Control (tinyurl.com/29zmmhl) and the Food and Drug Administration (tinyurl.com/2wvgxa3).

The risk of BSE led to valid concerns, not only about tainted meat, but about the use of cow byproducts.

Gelatin is a type of protein that can come from bones and hides of cattle, but it usually comes from pork. Irrespective of the animal source, the tissues used to make gelatin are considered by the FDA to be low-risk for the spread of BSE. In addition, the FDA published a guidance in 1997 that prohibits the making of gelatin from high-risk cows (tinyurl.com/nc8t45t).

We next consider the fact that the manufacturing process by which gelatin is made involves acid and alkali treatments and extensive washing coupled with high temperature sterilizations. Each of these steps further reduces risk. While it is always difficult to speak in absolutes, the process does make the risk negligible, and, as such, gelatin retains its "generally regarded as safe" designation as an ingredient in foods, or as an ingredient in medications or dietary supplements.

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.