Controlling organic acids impacts sour taste.

Sour is one of only five primary human taste sensations, and it is stimulated by organic acids. Some organic acids are naturally present in foods, such as the citric acid in oranges, malic acid in apples, and, as a result of fermentation, the lactic acid in yogurt. These and other organic acids may also be used as food ingredients.

Food processors may soon have more control over the amount of sour taste that comes through in a variety of acidified food products, thanks in part to new research led by USDA-ARS scientists, who collaborated with colleagues at North Carolina State University, Raleigh, NC. Their study is appearing in the August issue of the Journal of Food Science. Their new insight will help processors more efficiently control sour taste intensity when formulating acidified foods, such as sour candies, cream dressings, dill pickles, dough breads and tangy beverages.

Since taste is a subjective perception, nine volunteers were trained to evaluate the intensity of sourness, plus several other sensory attributes. The volunteers were presented with test solutions containing eight different organic acids--either with one acid at a time, or as a mixture containing three of the acids.

Organic acids are molecules characterized by the presence of carboxyl groups, which make them acidic. Surprisingly, molecules of all eight organic acids were perceived to be equal in sour taste, provided that at least one carboxyl group in a molecule had a hydrogen ion attached to it. When no hydrogen ion was attached, no sour taste was detected at all.

The scientists also tested these chemical relationships in a food. They made fresh-packed dill pickles using the same organic acids used in the test solutions. Experiments showed that the sour taste intensity increased in direct proportion to the total number of all organic acid molecules in the pickles that had an attached hydrogen ion.

Further information. Roger Mcfeeters, USDA-ARS Food Science Research Unit, 322 Schaub Hall, North Carolina State University, Campus Box 7624, Raleigh, NC 27695; phone: 919-515-2990; fax: 919-513-0180; email: roger.mcfeeters@ars.usda.gov.