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OPTIMIZATION OF THE EXTRACTION OF VOLATILE COMPOUNDS FROM AROMATIC RICE BY HS-SPME/GC-MS USING A CENTRAL COMPOSITE ROTATABLE DESIGN

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Aromatic rice differentiates itself from traditional rice due to its attractive aroma and remarkable characteristics. Its volatile compounds responsible for the aroma can be easily perceived when it is cooked. The aim of this work was to optimize the extraction of volatile compounds from aromatic rice by HS-SPME/GC-MS using a central composite rotatable design (CCRD), constituted of a 22 factorial design with 4 replicates of the central point, totaling 12 experiments. The independent variables were sample mass (X1) and pre-incubation temperature (X2). Axial points varied from 0.5 to 2.5 g for X1 and from 70°C to 90°C for X2. After that, an extraction kinetic studied was carried out at 80°C and 90°C to establish the best times of pre-incubation (15, 30, 60 and 120 min) and fiber exposure in the HS (5, 10, 20 and 30 min). Rice was ground in a mortar and pestle, weighted in 20 mL vials and analyzed by HS-SPME/GC-MS. The software Protimiza Experimental Designer was used to analyze the results at a 5% significance level. The analysis of the response surfaces showed that the higher the sample mass and pre-incubation temperature, the higher the chromatographic areas of the compounds of interest. Considering the lowest area value of hexanal, a marker of lipid oxidation, and the highest area value of 2-acetyl-pyrroline, main responsible for the aroma of aromatic rice, the optimized conditions were 2.5 g of sample, extraction at 80 °C and pre-incubation for 60 min. In addition, time of fiber exposure in the HS was established at 10 min, since results presented the lowest coefficient of variation. By using the conditions optimized by means of the CCRD, 27 volatile compounds were identified in aromatic rice.