Time-intensity curves

G. Dijksterhuis and P. Filers, Modelling time-intensity curves using prototype curves. Food Qual. Pref., 8 (1997) 131-140. 

If the reactants in a type I chemiluminescence reaction are rapidly mixed they will result in an emission whose intensity Ia, can be measured as a function of time. A typical time intensity curve for a CL reaction is shown in Figure 2. 

Figure 1. Mean time-intensity curves for bitterness of white wine with 8 and 14 % (v/v) ethanol (n=24 judges x 2 reps. The arrow denotes expectoration at 10 sec. (9).

Figure 8. Mean time-intensity curves for astringency for 9 low-flow and 9 high-flow judges pooled across 10 red wines (Reproduced with permission from reference 29. Copyright 1995.)...

Numbers represent the m/z values of the compounds, S represent the sensory score, the following descriptors denote the parameters derived from analysis of die aroma release and time intensity curves (see Experimental for detaUs). Reproduced from reference 15. Copyright 2003 Lavoisier... 

Despite their widespread use in the brewing literature the use of thresholds has been criticized [28]. Thresholds are but one point on a dynamic concentration continuum . There is no evidence that the intensity/concentration curves for all substances are parallel differing only in the point where they cross the abscissa. Further, taste is not a single instantaneous sensation but has a temporal element. Tasters have been trained to record the intensity on a scale between 0 (none) and 100 (extreme) on a moving recorder chart whereby a time-intensity curve such as Fig. 23.6 is obtained [26-28]. Typically the sample was expectorated, or if beer swallowed, after ten seconds. As would be expected when a sucrose gelatine was expectorated the intensity of the sweet sensation immediately started to fall and declined to zero in about 10 s [26]. 

Fig. 23.6 Average time-intensity curves for bitterness of four levels of iso-a-acids in commercial lager. Samples were placed in the mouth at zero times and swallowed at 10 s. The jud e continued to record intensity of bitterness until disappearance or for a maximum of 2 min. (After Lewis et al. [26].)...

Figure 3 Mean time-intensity curves for strawberry flavor perception, resulting from pumping and mixing solutions of citric/malic acids, sucrose, and a strawberry aroma. Initially all three components (acids, sucrose, strawberry aroma) were present. After 30 seconds either one, two, or all three of the solutions were replaced by an equivalent flow of water (see key). After 180 sec, the mixture was restored to its initial state. 1, Aroma off 2, sucrose off 3, acid off 4, aroma and sucrose off 5, aroma and acid off 6, acid and sucrose off 7, all off.

The trapezoid method allowed modeling of the experimental time-intensity curves, in order to extract characteristic times and intensities [19]. This is shown in Fig. 1. In particular, this treatment of time-intensity curves allows the calculation of the total duration and area of the perception. 

Ten panelists, six products, one attribute, and two replications amounted to 120 time-intensity curves. An analysis of variance and the least significant difference (LSD) were computed for each primary and secondary parameter. 

Figure 3 Average skeleton time-intensity curves of fruity sensory attribute."...

M Lallemand, A Giboreau, A Rytz, B Colas. Extracting parameters from time-intensity curves using a trapezoid model The example of some sensory attributes of ice cream. J Sens Stud 14 387-399, 1999. 

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