3.4. Fatty acid analysis
The characterization and quantification of fatty acids are shown in Table 2. The results on lipid composition correspond only to the free fatty acid fraction. In addition, there is substantial difference between the current study using GC/FID and Garrote et al. (2007) in which MS was coupled with GC. Refluxing for 120 min resulted in the significantly highest amount of total fatty acids, followed by 60 and 30 min (p < 0.05). Although valeric acid was not detected under this condition, the RD6 rice husk cultivar contained higher fatty acid contents than a previous report of the rice cultivar grown in Spain (Garrote et al., 2007). The amount of fatty acid content was in accord with the extract yield, antioxidant activity and active principle contents, which were determined using the TPC and TFC measurements. Correlation between activity and active compounds were further monitored. The TPC was most related with antioxidant activity (r = 0.997), followed by total fatty acid content (r = 0.864), whereas TFC was not related (r = 0.004). Furthermore, linoleic acid was positively related with TPC (r = 0.986) and exhibited an antioxidant response (r = 0.996). Furthermore, linoleic acid from 120 min extraction was significantly higher than 30 and 60 min (p < 0.05). This report studied Thai rice in particular, and refluxes of 60 and 120 min of the husks resulted in higher contents of heptanoic, nonanoic, oleic and linoleic acids compared to Spanish rice (Garrote et al., 2007).