Isoflavone-rich extracts from okara using supercritical fluid extraction: Kinetic modeling and characterization

The lipid fraction and bioactive compounds from okara, a by-product of soybean processing, have been extracted by supercritical fluid extraction. The effect of operating parameters, pressure (20–40 MPa), temperature (40–80 ºC), and cosolvent usage (0–10 %wt. ethanol), on the extraction kinetics has been investigated, satisfactorily correlating the experimental data to the Sovov´ a’s model. Extraction yield by SFE ranged from 0.1014 g extract/g insoluble solid (IS) at 20 MPa and 80 ºC to 0.1081 g extract/g IS at 30 MPa and 60 ºC (from 9.2 to 9.8 g extract/100 g okara, respectively), similar to Soxhlet extraction with n-hexane (9.2 ± 0.2 g extract/100 g). Pressure positively affected the initial extraction rate, which also increased with temperature except for the lowest pressure of 20 MPa, exhibiting a typical cross-over behavior. The use of ethanol as cosolvent promoted the extraction of phenolic compounds and isoflavones, and was less important in the extraction of tocopherols. Extraction yield using ethanol increased up to 0.1100 g extract/g IS at 40 MPa and 40 ºC. As expected, the higher content of bioactive compounds in the sc-CO2 + ethanol extracts positively affected the antioxidant capacity, with the maximum found at 20 MPa, 40 ºC and 10 %wt. ethanol.

Financial support from Agencia Estatal de Investigacion ´ (AEI) and Ministerio de Ciencia e Innovacion ´ (MICINN) [grant number PID2022–136385OB-I00], from the AEI, MICINN, and NextGener ationEU [grant numbers TED2021–129311B-I00 and PDC2022–133443-I00] and from Junta de Castilla y Leon ´ (JCyL) and European Regional Development Fund (ERDF) [grant number BU027P23] is gratefully acknowledged. E Díaz de Cerio contract was funded by JCyL and ERDF through project BU050P20. P. Barea contract was funded by JCyL and the European Social Fund (ESF) by Orden EDU/ 1868/2022, de 19 de diciembre; R. Melgosa contract was funded by a Beatriz Galindo Research Fellowship [BG20/00182]; A.E. Illera contract was funded by JCyL and ERDF through project BU027P23.