Consumer interest in food labels is growing, and so is their frustration at what they see, according to consumer polling done by a newsletter aimed at marketers.

"An aging and dieting population is concerned about toxic substances, watching out for fats and sodium and increasingly frustrated by small print," reports Mona Doyle in The Shopper Report.She says in a recent edition of her newsletter that consumers are becoming increasingly irritated by labels that seem to be written in a foreign language.

"They are frustrated sugar hides behind a lot of different names and whenever a product lists unintelligible ingredients . . . They are frustrated by the many meanings of `lite, which range from low salt, to low fat or low sugar,' " she wrote.

Doyle, who surveys a panel of 3,500 shoppers regularly and reports on their preferences and irritations for her Philadelphia-based newsletter, says many consumers would like explanations of food terms in layman's words.

Most foods do list their ingredients on the label, and the Food and Drug Administration requires that listing to use what it considers their "common and usual names."

In addition, under federal rules ingredient lists have to show the ingredient present in the largest amount - by weight - first, followed by other ingredients in order of weight.

Some foods like peanut butter, for which there are government standards for ingredients, do not have to have such a list; but most do anyway.

The FDA reports that it has surveyed consumers and found most have a basic understanding of such terms as calcium, preservative and sodium. But knowledge was much less over such common ingredients as riboflavin, emulsifier and humectants.

The FDA published a list of common ingredient terms in the March edition of its magazine, FDA Consumer. Some of these include:

- Acidulants or acidifiers: Acids used to improve flavor, prevent growth of bacteria, prevent discoloration or rancidity or to balance the acid level of a food.

- Anti-caking agents: Substances used to prevent powdered or granular foods from absorbing moisture and becoming lumpy.

- Antioxidants: Preservatives that prevent or delay discoloration of food and help keep oils and fats from turning rancid. These include BHA, BHT and propyl gallate.

- Cholesterol: Fat-like substances found in foods of animal origin but not plant based foods. Cholesterol is needed by the body, but too much can increase the risk of heart disease.

- Emulsifiers: Agents that stabilize fat and water mixtures so they will not separate.

- Flavor enhancers: chemicals such as monosodium glutamate, disodium guanylate and disodium inosinate which improve flavor.

- Humectants: Chemicals such as glycerol, propylene glycol and sorbitol that are added to foods to help them retain moisture, fresh taste and texture.

- Leavening agents: Substances such as yeast and baking powders that are used to make foods light in texture by forming carbon dioxide gas in dough.

- Light or lite: A term that suggests that a food is lower in calorie content, unless some other meaning is specified. Check such labels carefully for calorie, fat and sodium content.

If a food is labeled "low calorie" it must have no more than 40 calories per serving and 0.4 calories per gram. "Reduced calorie" means a food has at least one-third fewer calories than the food it is being compared to.

- Natural: Widely used, this word has no official meaning on food labels.

- Niacin: Water soluble B vitamin important for body cells.

- Riboflavin: Another water soluble B vitamin, needed for the nervous system.

- Sequestrants: Chemicals used to bind trace amounts of metals or other impurities that can cause food to become discolored or rancid.

- Sodium: A common ingredient also found in salt and often linked to high blood pressure. Sodium-free means less than 5 milligrams of sodium per serving; very low sodium means less than 35 milligrams per serving and low sodium means 140 milligrams or less.

- Stabilizers or thickeners: Substances that give food a smooth, uniform texture. These include food starches, carrageenan, locust bean gum, agar agar, sodium alginate, gelatin and pectin.

- Sugar: Common sugars in foods are table sugar (sucrose), fructose and corn syrup. A food can be labeled sugar free and still contain calories from sugar alcohols such as xylitol, sorbitol and mannitol, if the basis for the claim is explained.