Aroma Model, Omission Experiments

The highest OAVs were found for 4-hydroxy-2,5-dimethyl-3(2H)-fura-none, followed by ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, methyl 2-methylbutanoate and ( ,Z)-l,3,5-undecatriene. It is assumed that these odorants contribute strongly to the aroma of pineapples [50]. However, FD factors and OAVs are functions of the odorants concentrations in the extract, and are not psychophysical measures for perceived odour intensity [71,72]. To take this criticism into account, aroma models are prepared on the basis of the results of the quantitative analysis (reviewed in [9]) and in addition omission experiments are performed [9]. 

In the case of pineapples, the 12 odorants listed in Table 16.7 were dissolved in water in concentrations equal to those determined in the fruit [50]. Then the odour profile of this aroma model was evaluated by a sensory panel in comparison to fresh pineapple juice. The result was a high agreement in the two odour profiles. Fresh, fruity and pineapple-like odour notes scored almost the same intensities in the model as in the juice. Only the sweet aroma note was more intense in the model than in the original sample [50]. In further experiments, the contributions of the six odorants showing the highest OAV (Table 16.7) were evaluated by means of omission tests [9]. The results presented in Table 16.8 show that the omission of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, ethyl 2-methylbutanoate or ethyl 2-methylpropanoate changed the odour so clearly that more than half of the assessors were able to perceive an odour difference between the reduced and the complete aroma model. Therefore, it was concluded that these compounds are the character-impact odorants of fresh pineapple juice. 

Grosch, W. (2001). Evaluation of the key odorants of foods by dilution experiments, aroma models and omission. Chem. Senses, 26, 533-545. 

Comparison of the overall odour of the aroma model with that of models in which one or more components are omitted (omission experiments)... 

In the dilution experiments, on which the aroma models are based, the odour impact of the volatiles is evaluated after separation by GC (cf. 6.2.4.2.2). Perceptual interactions of odorants, which in most cases were characterised by inhibition and suppression [8, 36], are excluded by this procedure. Therefore, the question as to which compound among the volatiles evaluated by the dilution experiments actually contributes to the aroma has to be answered by omission experiments (step 7 in Table 6.23). Examples of such experiments are given in 6.2.4.3. 

An aroma model was very similar to the aroma of the juice when it contained 0.1% fat in addition to the volatiles listed in Table 6.38 [67], The terpene-like odour quality was decreased and the fruity note was enhanced. Omission experiments (Table 6.39) revealed that only the absence of acetaldehyde (no. 1) and (R)-limonene (no. 19) was detectable with high significance (a = 0.1) by either nasal or retronasal evaluation. Retronasally an aroma difference between the complete model and the model, in... 

Some omission experiments, e. g., conducted with the aroma model for French fries, are shown in Table 5.15. 

By AEDA the four odorants shown in Figure 9 were detected with the highest FD-factors in dill herb [33], A mixture of these compounds, dissolved in water at the same concentration ratios occurring in the herb (Table 16) very much resembled the typical odor of the dill herb. If (S)-a-phellandrene or the dill ether (B and A Fig. 9), respectively, were omitted, the mixture lost its typical odor note. On the contrary, omission of myristicin and methyl 3-methylbutanoate (D and C Fig. 9) did not significantly influence the overall dill herb aroma of the model mixture [33, 66], The data indicated that (S)-a-phellandrene and the dill ether are the character impact compounds of the dill herb. Since, on the basis of AEDA or calculation of OAVs further odorants have been shown to contribute to the dill herb flavor [33, 66], the results of the simulation experiments revealed that obviously the two monoterpenes are able to mask the flavor contributions of these compounds. 

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