Q. I have a friend who insists that even though labels on frozen foods always warn against refreezing, it is a perfectly safe practice. If that's true, why the package warning?

A. The original reasoning behind the warning had as much to do with quality as it did with concern for safety. Pioneers of the frozen food industry, eager for consumer acceptance, were particularly interested in preserving the quality of their products.

As you know, thawing and refreezing almost always affect the quality of food. However, not all foods are affected equally. Fruits and vegetables, for example, tend to suffer more than red meat. So do prepared dishes.

From the standpoint of safety, whether a particular food can be refrozen depends on how long it has been thawed and how it was handled both during and after the thawing process. Foods that still contain ice crystals or are still cold or that have been held in the refrigerator no more than a couple of days after thawing can generally be refrozen safely. On the other hand, a casserole that has thawed for several hours in a warm kitchen should not be refrozen. (In fact, to be perfectly safe, food should always be thawed by being placed in the non-freezer part of the refrigerator.)

Refreezing, however, not only affects the eating quality, but also usually causes vitamin loss. Therefore, to maintain taste and nutrition, refeezing should be used only as a last resort. If you do refreeze, try to use those foods as soon as possible.

Q. Could you please explain the difference between chocolate and cocoa? Is either of them acceptable on a cholesterol-lowering diet?

A. Both coca and chocolate are made from the seeds of the pods of the cacao tree. The seeds are fermented to decrease the bitter taste, roasted to develop flavor, shelled and cracked.

In making chocolate, the cracked seeds - or "nibs" - are ground at a warm temperature, producing a liquor containing not less than 50 per cent and not more than 58 per cent cacao fat.

Under the federal standards of identity cacao fat or cocoa or both may be added in amounts necessary to adjust the fat content ofthe finished liquor.

In making cocoa, some of the fat is removed from the ground nibs before they are pulverized. But how much fat remains can vary. For example, breakfast cocoa, a high-fat cocoa, contains a minimum of 22 per cent fat. Medium-fat cocoa contains at least 10 per cent but not over 22 per cent fat, and low-fat cocoa contains less than 10 per cent cacao fat.

Obviously, then, chocolate is simply too hightin fat for anyone interested in cutting down on his or her total fat comsumption. But if chocolate flavor is something you really miss, you can occasionally use cocoa to make a sherbet topping, a chocolate-flavored low-fat rice pudding or an icing for angel cake.

Q. Could you please tell me why flour is bleached?

A. Refined white flour is one of those foods that improves with age. When freshly milled, it has a rather yellowish color and produces baked products with a relatively low volume and coarse texture. If allowed to stand for several months, however, natural oxidation takes place. The flour whitens, the texture becomes finer and the baking quality improves.

Natural aging is somewhat impractical however. It requires both time and enormous amounts of space. Moreover, the flour must be carefully protected against insects and vermin.

Starting at the beginning of the century, food technologists found that they could use bleaching and maturing agents that would quickly achieve the same effect as natural aging. An undesirable effect of the additives approved for this purposes is that some of them destroy vitamin E. But white flour is not an important source of vitamin E to begin with.

Currently both bleached and unbleached flours are readily available, and if a flour has been bleached it must say so on the label. Since they are just about nutritionally equal, which one you use is really a matter of individual preference.