## 3 Results and Discussion
### Evaluation of Volatile Organic Compounds
Regarding the ketone group, 1-hydroxy-2-propanone, and 1-(2-furanyl)-ethanoneone, which are related to negative attributes  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multicolumn{1}{c}{**Volatile Organic Compounds**} & **WR1** & **WR2** & **WR3** & **WR4** & **P1** & **P2** & **P3** & **P4** \\ \hline \multicolumn{1}{c}{**Hydrocarbons**} & & & & & & & & \\ \multicolumn{1}{c}{**Heptane**} & 10.9 & 12.6 & 6.0 & 0.4 & n.d. & n.d. & n.d. & n.d. \\ \multicolumn{1}{c}{D-limonene} & 3.3 & 3.0 & 3.2 & n.d. & 4.2 & 4.8 & 2.9 & n.d. \\ \multicolumn{1}{c}{p-Xylene} & n.d. & n.d. & n.d. & n.d. & n.d. & 1.9 & 1.8 & 0.5 \\ \multicolumn{1}{c}{o-Xylene} & 6.9 & 8.7 & 6.4 & 2.5 & n.d. & n.d. & n.d. & n.d. \\ \multicolumn{1}{c}{Styrene} & 1.4 & 1.9 & 10.5 & 0.0 & 1.2 & 1.4 & 0.8 & n.d. \\ \multicolumn{1}{c}{TOTAL} & 22.4 & 26.2 & 26.2 & 2.9 & 5.4 & 8.0 & 5.5 & 0.5 \\ \multicolumn{1}{c}{**Ketones**} & & & & & & & & \\ \multicolumn{1}{c}{2-Propanone, 1-hydroxy-  
such as roasted [37] and spicy [31], respectively, appeared only at the last sampling time (WR4 and P4). In the alcohol group, 3-cyclohex-1-ol was found only in paella rice, increasing with processing time because it is related to the shellfish aroma [35]. On the contrary, 2-ethyl-1-hexanol, which is related to sweet and slightly floral-pink aromas [36], appeared only in white rice (WR1 and WR2). 2-Furanmethanol, which is associated with roasted aromas [34], was found at the last sampling time for both rice samples. Regarding the aldehyde group, benzaldehyde compounds were the main aldehydes found in white rice, and their quantity decreased with the processing time. These compounds are related to almond aromas [42]. Hexanal, octanal and nonanal, which are related to positive aromas such as fruity [31], citrus [43] and sweet [44] odors, were present in both rice samples, but decreased at the end of the processing time. 5-Methyl-2-furancarboxaldehyde, which is associated with smoky aromas, was found at a high intensity at the end of the thermal treatment, being higher for white rice. This result can be related to the sensory analysis (Table 2), where the burnt aroma was higher in white rice compared to paella rice (for the last sampling time), which was probably due to the formation of the socarrat that delays or prevents rice burning. In the pyrazine group, it is worth highlighting methyl-pyrazine, 2,6-dimethyl-pyrazine and trimethyl-pyrazine, which appeared during thermal treatment and which are associated with varnish and roasted aromas [45]. Sulfur compounds were only found in paella rice due to the added ingredients and their transformation during processing. 2-propenyl trisulfide has been found in garlic, onion and green aromas [31], and also decreased significantly with the processing time. Diallyl disulfide and diallyl sulfide, which are associated with spicy and green aromas [31], respectively, increased slightly with thermal treatment, probably due to the cooking of the ingredients. Furan and furanone compounds, which are related to roasted, bitter and caramel aromas [30; 32; 38; 31], were found at the end of the processing time in WR and P. Furfural was the one that was found with the highest intensity in WR, which coincides with the previous analysis of 5-methyl-2-furancarboxaldehyde and the sensory analysis results that found a greater bumt aroma at the end of the processing time in WR compared to P. In general, these furan and furanone compounds can be formed by the Maillard reaction by heating carbohydrates [29].