RESUMO
The conversion of isoflavones during subcritical water extraction were studied using first-order reaction kinetics modeling. Isoflavones were extracted from soybean using temperatures from 100â to 180â for 3 to 30 min. It was found that malonylgenistin was the most thermally unstable, with little being detected above 100â. The optimal extraction temperatures for acetylgenistin (AG), genistin (G), and genistein (GE) were 120â, 150â, and 180â, respectively. A larger sum of the numbers of both hydroxyl groups and oxygen molecules was associated with a lower melting point and optimal extraction temperature. Kinetics modeling of reaction rate constant k and activation energy Ea showed that all of the reaction rates tended to increase with temperature, with the relationship fitted well by a first-order model in nonlinear regression. For temperatures between 100â and 150â, AG â G and AG â GE conversions showed the highest rate constants, but G â GE and G â D3 (degraded G) conversions became dominant at 180â. Chemical compounds studied in this article: genistein (PubChem CID: 5280961), genistin (PubChem CID: 5281377), 6â³-O-malonylgenistin (PubChem CID: 15934091), 6â³-O-acetylgenistin (PubChem CID: 5315831).
