Accelerated storage conditions effect on ginger- and turmeric-enriched soybean oils with comparing a synthetic antioxidant BHT

Commercial and freeze-dried powders of ginger and turmeric rhizomes were incorporated in the soybean oil at the concentration of 10% (w/w) to develop a food seasoning containing natural antioxidants to improve lipid stability. The phenolic composition, antioxidant activity, and oxidative stability of ginger- and turmeric-enriched soybean oils were evaluated during storage at 62 °C for 28 days. The phenolic characterization was performed by detecting total polyphenols through Folin-Ciocalteu assay and HPLC analyzing 6-gingerol and curcumin, respectively. The antioxidant activity was spectrophotometrically measured through 2,2-di(4-tertoctylphenyl)-1-picrylhydrazyl (DPPH) radical scavenging capacity and ferric ion reducing antioxidant power (FRAP) assays. The peroxide value (PV) and induction period (IP) have been determined through spectrophotometric and Rancimat methods thus monitoring the primary and secondary phases of lipid oxidation, respectively. The addition of freeze-dried powders derived especially from turmeric rhizome contributed to enhanced antioxidant activity and oxidative stability of soybean oil under accelerated storage conditions thanks to its enrichment in bioactive compounds highly resistant to thermal degradation. Hence, ginger and turmeric powders can be valorized as functional ingredients to be incorporated in vegetable oils for preventing their lipid structure against to oxidation, and simultaneously providing health benefits to consumers.