# Aroma Compound Release from Starches of Different Origins: A Physicochemical Study
## 5 Discussion  
From the results listed in Table 3 regarding the evaporation of aroma compounds from the bulk liquid phase, the following conclusions can be drawn:  
1. The values of \(k_{\rm c}\) increased with the temperature, which is in accordance with previous results [54], although the increment in the case of dl-limonene is smaller than in the case of diacetyl. The values of the mass transfer coefficient for each temperature are higher for diacetyl than for limonene. The higher the temperature value, the greater the difference in values. The latter could be attributed to the higher boiling point of dl-limonene compared to the boiling point of diacetyl. 2. The above is supported by applying statistical analysis (one-way ANOVA, \(P\leq 0.01\)) to the mean value of the mass transfer coefficient at each temperature. All values are statistically different, except for the mean values corresponding to the temperature of 303.15 K.
3. The polar nature of diacetyl and the non-polar nature of dl-limonene may be the cause of the variations in the activation energies, \(E_{\rm a}\), needed for the evaporation of diacetyl and dl-limonene from the bulk liquid. The differences in the calculated activation energies, \(E_{\rm a}\), needed for the evaporation of diacetyl and dl-limonene from the bulk liquid could be attributed to the polar character of diacetyl and the non-polar character of dl-limonene. Van der Waals dipole-dipole interactions could be present at the polar diacetyl, while the non-polar dl-limonene could not develop such interactions. From the results listed in Table 4, as well as from Figures 9 and 10, the following conclusions can be drawn:  
1. The values of \(k_{\rm c}\) increased with the temperature in all cases. These values are in accordance with the results given in the literature [55] for the mass transfer coefficient of diacetyl from stirred water. Although the values of \(k_{\rm c}\) increased with the temperature in each system, comparing the values of two aroma compounds with the same starch at the same temperature does not show a pattern. In the case of the systems aroma compounds and wheat, the \(k_{\rm c}\) values are statistically different for the two aroma compounds at all temperatures, while in the case of the systems aroma compounds and corn, the \(k_{\rm c}\) values are statistically different only at the highest temperature. This may also explain the small difference observed in the activation energy for the two systems (diacetyl + corn and dl-limonene + corn). 2. The different variations in \(k_{\rm c}\) values with temperature for the diacetyl + starch systems (from corn, rice, and potato) compared to those of the diacetyl + starch system from wheat suggest different mechanisms of diacetyl release for these different starches. On the other hand, the release of dl-limonene seems to follow the same mechanism for wheat- and corn-derived starches and a different mechanism for rice- and potato-derived starches. These conclusions are also supported by the activation energy values. The activation energies needed for the release of diacetyl from starches derived from corn, potato, and rice have the same values (more or less), whereas for release from starches derived from wheat, the activation energy requirement was calculated to be about four times higher. Also, the activation energy requirements for the release of dl-limonene from starches derived from corn and rice are (more or less) the same, while somewhat smaller values for the dl-limonene + potato and dl-limonene + wheat systems have been calculated. 3. The calculated activation energy, \(E_{\rm a}\), needed for the release of diacetyl from wheat was found to be equal to 98.65 kJ mol\({}^{-1}\), indicating chemical sorption of the polar compound diacetyl (ketone). This could be attributed to the fixation of the polar molecule of diacetyl by amino groups of proteins, since wheat starch has the highestprotein content compared to starches from other botanical sources.