A longitudinal comparison of two salt reduction strategies and acceptability of a low sodium food

Abstract

The overall objective of the two studies detailed herein was to contribute to our current understanding of how best to approach population-wide dietary salt reduction in the event of a salt mandate, as recommended by the Institute of Medicine (IOM) via their publication, <italic>Strategies to Reduce Sodium Intake in the United States</italic>. In order to determine how much salt could be reduced in a food and remain unnoticed by consumers, the objective of the first study was to determine a series of sequential difference thresholds for sodium chloride detection in plain water and in water with added taste stimuli to simulate a more complex flavored broth. Ten subjects were recruited from a trained descriptive analysis panel of PROP tasters and supertasters. Using paired comparison tests, difference thresholds were established for each of the two described solutions starting at a salt concentration comparable to that of commercially available soup, and ending at a concentration required to meet FDA low sodium guidelines. From these thresholds, two series of concentrations were established: a 26 step reduction for salt in water, and a 12 step reduction for salt in water with added stimuli. The difference in number of steps illustrates the importance of product complexity in determining sensitivity to sodium reduction and provides basic information for manufacturers interested in gradually decreasing salt content of foods without detection by consumers. The objective of the second study was to compare two salt reduction strategies over a 16-week period to determine if gradual salt reduction, as recommended by the IOM, was more effective than abrupt salt reduction for maintaining acceptability of a low sodium food. Eighty-three subjects participated in a three-part study: an initial taste test, a 16-week longitudinal study, and a final taste test. At the initial and final taste tests, subjects indicated liking of tomato juice at four salt concentrations ranging from 136mg sodium/serving (low sodium) to 640mg sodium/serving (a salt concentration comparable to a commercially available product). To create two groups for the 16-week study, subjects were balanced for motivation to reduce dietary salt intake, sensitivity to 6-n-propylthiouracil, and hedonic sensitivity to salt (the difference in liking between the highest and lowest salt concentrations in tomato juice served at the initial taste test). One group received juice abruptly reduced in salt to a target low sodium level at week 5; the second group received juice gradually reduced in salt via difference threshold steps determined in the first study to reach the target at week 14. Liking for reduced salt and low sodium juices increased between taste tests; in addition, subjects experienced a downward shift in salt preference as a result of repeated exposure to reduced salt and/or low sodium juice during the longitudinal study. No overall difference in liking for low sodium juice was observed at the end of the longitudinal study between subjects in the abrupt and gradual salt reduction groups; however, differences in liking as a result of hedonic sensitivity and motivation indicate gradual step-wise salt reduction is not a `one size fits all' approach.