Original research articleIonic liquid-based ultrasound-assisted extraction coupled with liquid chromatography to determine isoflavones in soy foods

•HPLC-DAD method was developed for the determination of isoflavones in soy products.•ILUAE procedure was optimised by evaluating the influence of several parameters.•ILUAE: 0.2 g of sample soaked in 2 mL of [C6MIM]Br and ultrasonicated for 40 min.•ILUAE method proposed shows potential as an environmentally-friendly technique.•ILUAE-HPLC-DAD was used for the analysis of isoflavones in food samples.

An ionic liquid-based ultrasound-assisted extraction (ILUAE) was developed to extract four isoflavones, genistin, genistein, daidzin, and daidzein, from soy products. Various 1-alkyl-3-methylimidazolium compounds were investigated and 1-hexyl-3-methyl-imidazolium bromide ([C6MIM]Br) (1 M) was selected as the solvent. Several extraction variables, such as ionic liquid concentration, extraction time and solid/liquid ratio were also investigated. A method to determine the isoflavones by high-performance liquid chromatography (HPLC)-diode-array detection (DAD) was developed. Under the optimal extraction and chromatographic conditions, the isoflavones exhibited a good linear relationship, between 2.5-50 μg/g for daidzin and 0.5-50 μg/g for genistin, genistein and daidzein. The precision and accuracy of the proposed method were <7% and between −8.5 and 12%, respectively. The proposed method was successfully used to analyse soy food samples and the spiked recoveries ranged from 85.3 to 104%.

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