Published: April 22, 2011 r2011 American Chemical Society 5548 dx.doi.org/10.1021/jf2002848 | J. Agric. Food Chem. 2011, 59, 5548–5553 ARTICLE pubs.acs.org/JAFC Effects of Pulsation Rate and Viscosity on Pulsation-Induced Taste Enhancement: New Insights into TextureTaste Interactions Kerstin Martha Mensien Burseg,* ,†,§ Sara Camacho, §,# and Johannes Hendrikus Franciscus Bult †,§ † TI Food and Nutrition, P.O. Box 557, 6700 AN Wageningen, The Netherlands § NIZO Food Research BV, P.O. Box 20, 6710 BA Ede, The Netherlands # Instituto Superior T ecnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal ABSTRACT: Oral stimulation with high-tastant concentrations that are alternared with low-tastant concentrations or water rinses (pulsatile stimulation) results in taste intensity ratings that are higher than continuous stimulation with the same average tastant concentration. This study tested the combined effects of taste pulsation rate and viscosity on pulsation-induced taste enhancement in apple juice. According to a tastant-kinetics hypothesis, less pulsation-induced taste enhancement is expected at enhanced pulsation rates in the high-viscous proximal stimulus compared to lower viscous stimuli. High-concentration sucrose apple juice pulses and low-concentration sucrose apple juice intervals were alternated at different pulsation periods (pulse þ interval in seconds) every 2.5 s (period length = 5 s) or every 1.25 s (period length = 2.5 s). Pulsed stimuli were presented at two viscosity levels by the addition of pectin (0 and 10 g/L). Sweetness intensities of pulsed stimuli were compared to a continuous reference of the same net but nonalternating sucrose concentration. Sweetness ratings were higher for pulsatile stimuli than for continuous stimuli. In low-viscous stimuli, enhancement depended on the pulsation period and peaked at 5 s periods. In high-viscous stimuli, the same enhancement was observed for both pulsation periods. These results contradict a tastant-kinetics hypothesis of viscosity-induced taste suppression because impaired tastant kinetics by viscosity would predict the opposite: lower pulsation-induced taste enhancement for viscous stimuli, especially at higher pulsation rates. Instead, these observations favor an explanation based on perceptual texturetaste interactions, which predict the observed independence between viscosity and pulsation rate. KEYWORDS: pulsatile stimulation, aromataste interaction, texturetaste interaction, sweetness enhancement, pulsation period ’ INTRODUCTION For health reasons, regulatory bodies advise a reduction of sugar levels in foods. 1 As this conflicts with the innate preference for sweet taste, compensation strategies for low-sugar products are required. One strategy achieves taste enhancement by tastant concentration contrasts. 26 In liquid applications, tastant con- centration contrasts are evoked by stimulation with high-inten- sity tastant pulses that are alternated by tasteless or low-intensity tastant intervals. 4,5,7 This “pulsatile stimulation” enhanced sweet taste intensity of model solutions if compared to stimulation with the same net but not alternating (continuous) sucrose concentration. 4,5,7 Furthermore, the degree of sweet taste en- hancement by pulsatile stimulation depended hereby on different factors: the length of the pulsation period (summed length of pulse and interval in seconds), 5 the magnitude of the pulse- interval sucrose concentration contrast, 7 and the presence of additional flavor compounds such as a congruent aroma 4 or a qualitatively contrasting tastant. 7 Viscosity is another factor that might influence the degree of pulsation-induced taste enhance- ment. An increase in viscosity by the addition of (hydrocolloid) thickeners to tastant solutions commonly results in taste inten- sity reduction. 811 Kinetic explanations of this taste suppression suggest the involvement of reduced in-mouth tastant release and reduced diffusion rates. Tastant release and diffusion may be diminished due to binding of tastants to the thickener, the inhibition of transport of tastants from the bulk phase to the taste receptors, or inefficient tastant mixing in the solution due to entanglement in overlapping hydrocolloid chains. 1214 As for pulsatile stimulation, if concentration fluctuations in the distal stimulus are dampened as a result of decreased tastant mobility, the pulse-interval tastant concentration contrast in the proximal stimulus will be reduced 7 and decrease the taste intensity gain upon pulsation. Therefore, if increasing viscosity reduces tastant mobility, we hypothesized that increasing the tastant’s pulsation rate at high viscosity will reduce taste-contrasts in the proximal stimulus which, in turn, would reduce pulsation-induced taste enhancement in comparison to stimuli with a lower viscosity. In other words, increasing the stimulus viscosity is assumed to reduce tastant mobility, which in turn would suppress overall taste intensity as well as pulsation-induced taste enhancement. Alternatively, viscosity-induced taste suppression may not be caused by changes in tastant kinetics to start with. Possibly, the commonly observed taste suppression is caused by perceptual cross- modal inhibition as appears to be the case for viscosity-induced aroma suppression. 9,15 If tastant kinetics do not play a part in the observed viscosity-induced taste suppression, it is not expected that pulsation-induced taste enhancement is affected by viscosity. The tastant-kinetics hypothesis is tested in the present study by investigating the combined effects of viscosity and sucrose pulsation rate on the sweet taste of apple juice. This was real- ized by the alternation of high-concentration sucrose pulses and low-concentration sucrose intervals in apple juice. Apple juice Received: January 21, 2011 Revised: April 7, 2011 Accepted: April 9, 2011