# Effects of Pretreatment on the Volatile Composition, Amino Acid, and Fatty Acid Content of Oat Bran
## 3 Results and Discussion
### HS-SPME-GC-MS Analysis of Volatile Compounds of Oat Bran  
To further study the effect of different heating methods on the volatile composition of the oat bran, we used HS-SPME-GC-MS to determine the specific volatile components of the oat bran samples. The above chromatograms were retrieved by the NIST14 spectral library and the manual map analysis. The volatile compounds of the fresh and heated oat bran samples are shown in Table 2. A total of 64 volatile compounds from oat bran were tentatively identified and quantified, including 14 aldehydes, 12 esters, 10 alcohols, 5 ketones, 5 acids, 4 amines, 11 alkanes, 2 pyrazines, and 1 furan. A total of 43, 36, and 36 compounds were detected in OB, S-OB, and M-OB samples, respectively. It was noted that only 25 compounds were detected in HAOB. Among the 64 aroma compounds detected in oat bran, hexanal, nonanal, (E)-2-octenal, 1-octen-3-ol, 2-ethylhexan-1-ol, and 2-pentylfuran contributed the most. These compounds mainly contributed to the \"fresh\", \"green\", \"waxy\", \"aldehyde\", \"earthy\", and \"fruity\" characteristics. [PERSON] and [PERSON] [23] initially reported 111 volatiles in oat groats, hexanal was the most significant, with an odor threshold of 4.5 ng g\(-\)1, which was similar to the results of this experimental study. The high temperature could produce a variety of volatile flavor components by the Maillard reaction, lipid oxidation reaction, and amino acid degradation reaction [35]. Figure 1: PCA scatter plot of electronic nose in different pretreatments. OB, Oat bran; S-OB, Steamed oat bran; M-OB, Microwaved oat bran; HA-OB, Hot air dried oat bran. Aldehydes generally have the smell of cream, fat, vanilla, and fragrance. The aldehydes produced by the three heat treatment methods were absolutely dominant in relative content and quantity, and the thresholds of aldehydes were generally low, which greatly contributed to the overall aroma of oat bran and were the main volatile components of oat bran. Aldehydes accounted for 59.01%, 51.68%, 64.76%, and 68.13% of the volatile components in OB, S-OB, M-OB, and HA-OB, respectively. The aldehyde content of the oat bran increased with microwaving and hot air drying. This may be due to aldehydes derived primarily from the oxidation and degradation of unsaturated fatty acids [36]. In addition, increasing the temperature of oat bran samples may also promote the Maillard reaction, which increases aldehyde content [37]. Hexanal, heptanal, nonanal, (E)-hept-2-enal, and (E,E)-2,4-decadial mainly provided a grassy aroma. The content of hexanal in the HA-OB samples was highest (54.38%), followed by the M-OB content of 49.31%, and the S-OB was the lowest (36.49%). Similar results have been reported in other oats [20; 23]. The highest concentration volatile in oat bran is nexanal. The concentration of hexanal increases after heating. The contents of nonanal and (E)-2-ocreal in the S-OB and M-OB were higher than that in other samples. Nonanal presents waxy, citrus scents. The aroma produced by the aldehydes gives the oat bran its unique fragrance. Ten alcohols were detected in oat bran, including heptan-1-ol and 1-octen-3-ol, which were all identified in four samples. The content of 2-ethylhexan-1-ol in S-OB was higher than that in OB and M-OB. It was not detected in HA-OB. The odor of 1-octen-3-ol is often described as mushroom-like [38]. Aldehydes and alcohols played an important role in the flavor profiles of oat bran, which were consistent with previous research. Two other studies investigated the effect of heat treatment on the formation of volatile oats at various stages, from raw oat,, hulled, and dry hulled, to oat flakes [39; 40]. As shown in Table 1, OB had the highest amount of alcohols (17.94%), followed by the S-OB (15.10%) and M-OB(12.22%),