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Sour is one of only five primary human taste sensations, and 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.
Because 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 is what makes 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.
These chemical relationships were also tested in a food. Fresh-packed dill pickles were made using the same organic acids used in the test solutions. Taste tests 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.
This new insight will help food processors more efficiently control sour taste intensity when formulating acidified foods, such as sour candies, cream dressings, dill pickles, dough breads and tangy beverages.
The study, led by Agricultural Research Service (ARS) food technologist Roger McFeeters, will appear in the August issue of the Journal of Food Science. He and colleagues in the ARS Food Science Research Unit, Raleigh, N.C., worked with North Carolina State University-Raleigh researchers. ARS is the U.S. Department of Agriculture's chief scientific research agency.
By Rosalie Marion Bliss (July 5, 2007)
Agricultural Research Service, USDA: ( www.ars.usda.gov )
ARS is the U.S. Department of Agriculture's chief scientific research agency.
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