Perceiving the flavor of dietary fats.

From thick portions of fresh cream to a succulent roast dinner, most people associate fat with great taste and a satisfying meal, if not with a healthy lifestyle. We obviously need some fat in our diet, but the issue is: How much is too much? At the Centre for ChemoSensory Research (CCR, University of New South Wales, Australian Technology Park, Eveleigh NSW 1430 Australia), scientists are investigating the sensory properties of dietary fats.

While excessive fat intake contributes to obesity, heart disease, diabetes and cancer, there is a definite place for fats in a healthy diet. Dietary fats carry several essential fat-soluble vitamins. They provide us with fatty acids that help manufacture membranes and hormones. The recommended intake for fat is no more than 30% of dietary energy, with no more than one-third of this coming from saturated fats.

High-fat foods tend to dominate low-fat foods in popularity. Taste is still the dominant factor in repeat buying, so if a reduction in fat markedly affects taste, you may need to consider other ways of replacing the perceived flavor. Until recently, it was generally accepted that fat is sensed by means of textural cues and associated flavor alone, rather than by a chemosensory mechanism of its own. The crispness of potato chips and the oily coating they leave in your mouth; the smoothness of whipped cream and the cooling effect it has on your tongue; the moistness of chocolate cake--all of these textural features are created by the fat content of a product.

Fat appears to enhance flavor by interacting with other components in food. It may carry flavor molecules and deliver them to taste receptors, and it may mask or temper the strength of unpleasant flavors. The division of fat-soluble and water-soluble flavor compounds into separate phases dictates the flavor profile of a food. The slow release of flavors from the lipid phase gives a food its aftertaste.

With all of these functions to take into consideration, it's not surprising that the task of lowering fat content, or replacing fats in food, is so difficult to do well. For this reason, concentrating on textural cues for fat is probably simply not enough. Recent evidence suggests that receptors for fats and fatty acids are present on the taste cells of the tongue. They convey information about fats to the brain as do receptors for sweet, sour, bitter or salty tastes, explain researchers at the Australian center.

Knowing that fats act by interacting with receptors makes it possible to study fats by means of human sensory perception, using appropriately devised experimental strategies. Working with rats that had a tendency to moderate their fat intake when placed on a high-fat diet, researchers discovered that the taste receptor cells of this breed showed the greatest sensitivity to polyunsaturated fatty acids. This may be evidence that sensitivity to dietary fats is due to the expression of a gene.

Further information. Graham Bell; phone: [phone]; fax: [phone]; email: [e-mail].