Changes in taste and flavor in aging.

This study aims at understanding the role of mixtures (mutual quality suppression) in the evaluation of impact of the human aging process on the perception of taste. Heretofore, the effect of aging on taste has been directed at threshold and suprathreshold magnitudes of single chemicals (e.g., NaCl, sucrose, citric acid) in aqueous solution. Although absolute thresholds typically rise in advanced age (2 to 9 times, depending on the study), suprathreshold magnitude assessed by magnitude matching seems (except for bitter) to resist change in the way presbycusis spares suprathreshold loudness, fostering the impression that aging may handicap the aged little in the perception of food. Asked, however, to discriminate the presence-absence of the prescribed salt flavoring (nominally suprathreshold) in tomato soup, the young outperformed the middle-aged who, in turn, outperformed the elderly. Moreover, NaCl thresholds in the presence of tomato measured several times higher than in water, but the difference between the young and the elderly continued to hold. Elevation of threshold to much higher levels by mixture suppression leaves the young-elderly difference unchanged, implying that the elderly may fail to detect salt levels that really count in their diet. To examine the relation between age and taste mixtures, we measured detection thresholds: (1) for NaCl in citric acid, from zero to strong; (2) for sucrose in citric acid, from zero to strong; and (3) for citric acid in sucrose, from zero to strong. Whether in water alone or in a weak or strong suppressor, the elderly subjects' threshold was consistently 2 or 3 times higher than that of the young. Moreover, the way in which threshold for one quality rises with concentration of a suppressor is the same, except for constant upward displacement of the elderly peoples' threshold. In general, both young and elderly confuse salty and sour (show large suppression at all concentrations of the suppressor) much more than they confuse sweet and sour (seen mainly at high concentrations of the suppressor). Study of other mixtures is planned.