12-3 |
Utilizing the R-Index Method for threshold testing in model soy isoflavone solutions |
K. M. ROBINSON, B. P. Klein, and S. Y. Lee. Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, 260 Bevier Hall, 905 S. Goodwin Ave., Urbana, IL 61801 Soy isoflavones are nonvolatile, phenolic compounds that naturally occur in soy food products. Isoflavones are an important food component; they add health benefits by reducing the risk of certain cancers and heart disease. However, previous studies have labeled isoflavones as the bitter and astringent component in soy foods. These studies indicated low bitter/astringent thresholds for daidzein and genistein (aglycone forms), which have not been confirmed. The objective for this study was to establish difference thresholds for daidzein and genistein suspensions using the R-Index method. Genistein and daidzein (99% pure) were suspended in 0.5% (w/v) Mira Sperse 622® starch. Five concentrations were used for each isoflavone: 1.59*10-4 M, 4.81*10-4 M, 1.44*10-3 M, 4.33*10-3 M, and 1.30*10-2 M. An untrained panel of 28 people (9 males and 19 females) used the R-Index method to determine the difference thresholds for daidzein and genistein. The Mira Sperse® solution represented the noise and the isoflavone suspensions represented the signal. During each of three sessions, blindfolded panelists received five replicates of the noise and the five concentrations of an individual isoflavone in randomized order. To determine the threshold, the concentration at R-Index of 75% was calculated for each panelist and for the entire group. The 75% R-Index group thresholds for daidzein and genistein were 2.9*10-3 M and 4.0*10-3 M, respectively. The most and least sensitive thresholds in the group were 2.95*10-4 M and 1.21*10-2 M for Genistein and 3.5*10-4 M and 1.07*10-2 M for Daidzein, respectively. These results indicate a much higher threshold value than reported in literature. A typical aglycone isoflavone concentration for commercial soy milk is approximately 7.69*10-5 M. The thresholds found in this experiment are about 200-fold larger than this value and suggest that the soy isoflavones daidzein and genistein do not contribute to the bitter or astringent flavor in soy food products.
Session 12, Sensory Evaluation: Methods and consumer testing
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