Soil salinity modulates fatty acid composition and antioxidant capacity of rice bran oil

Rice bran oil (RBO) is valued for its nutritional and functional properties; however, the influence of soil salinity on RBO quality under field conditions remains insufficiently understood. This study examined RBO derived from two major Thai rice varieties, glutinous RD6 and non-glutinous KDML105, cultivated across saline-affected sites along the Siao Yai River in northeastern Thailand.

Soil chemical properties, including electrical conductivity of the saturated paste extract (EC_e), sodium adsorption ratio (SAR), exchangeable cations, and chloride, were evaluated in relation to RBO yield, γ-oryzanol content, antioxidant activity, elemental composition, fatty acid profiles, and synchrotron radiation-based Fourier transform infrared microspectroscopy (SR-FTIR) characteristics.

Soil salinity was strongly associated with variations in RBO compositional quality. Significant salinity effects were observed for specific saturated fatty acids, particularly stearic (C18:0) and arachidic acids (C20:0), which decreased under high-salinity conditions, and linoleic acid (C18:2n6c), which increased under high salinity. In addition, total polyunsaturated fatty acids (ΣPUFA) and fatty acid ratios, including monounsaturated fatty acids/saturated fatty acids (MUFA/SFA), polyunsaturated fatty acids/saturated fatty acids (PUFA/SFA), and unsaturated fatty acids/saturated fatty acids (UFA/SFA) were significantly higher under saline conditions, indicating a shift toward a relatively more unsaturated lipid profile. Antioxidant activity increased significantly with salinity and was positively associated with salinity indicators and unsaturated fatty acids, while carotenoid content was also higher under saline conditions and γ-oryzanol showed a variety-dependent response to salinity. In contrast, RBO yield was not affected by salinity, suggesting a potential decoupling between oil quantity and compositional quality, although this relationship warrants further controlled investigation. Calcium concentration in RBO increased under high salinity, suggesting a soil-oil linkage, whereas other elements showed limited responses. SR-FTIR analysis revealed comparable triacylglycerol spectral features across all samples, indicating that salinity-related differences were quantitative rather than structural.

These findings suggest that saline soil environments may enhance key nutritional and functional attributes of RBO without compromising oil yield, highlighting opportunities for valorizing RBO produced in saline-prone agricultural regions.