Comparative study of the methodology used in the extraction of isoflavones from legumes applying a modified QuEChERS approach

Introduction: Isoflavones are phytochemicals of great interest because of their association with a large variety of positive effects on human health. The major sources of isoflavones in the diet are plants of the Leguminosae family, especially soybeans, although many other legumes more widely consumed in the Mediterranean diet have also been reported to contain these compounds. In previous work we extracted isoflavones from samples using a modified QuEChERS (Quick Easy Cheap Effective Rugged Safe) methodology.

Objective: To compare different methods for placing the sample and the solvent in contact to optimise the extraction of isoflavones from legumes (chickpeas, lentils and white beans) using a modified QuEChERS methodology.

Method: Five different approaches to sample agitation were tested: vortex agitation, thermostatted stirring agitation and thermostatted tray shaking, and a thermostatted ultrasound bath and an ultrasound probe. To evaluate the different methodologies a modified QuEChERS approach was used as the extraction method. The separation and quantification of isoflavones was carried out using liquid chromatography-triple quadrupole/mass spectrometry (LC-MS/MS).

Results: The best methods were found upon using a thermostatted shaking tray for the extraction of chickpeas and white beans and the ultrasound probe for lentil samples. These methods were chosen based on the highest amount of analytes obtained as well as the best recovery values.

Conclusion: Determination of isoflavones in foods may be affected by the different methods used to place the sample and the solvent in contact in the extraction step. The main advantages of the proposed extraction procedures are their simplicity, speed, reliability and low cost.