טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentUngar Yael
SubjectDegradation and Modification of Soy-Isoflavones and the
Effects on their Bioavailability and Bioactivity
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Dr. Eyal Shimoni


Abstract

Isoflavones are considered to have a role in decreasing the risk of cardiovascular diseases and different cancers. Their stability and biological activities are strongly affected by processing and storage conditions. This study investigated the effect of thermal treatments on soy isoflavones, their stability, degradation kinetics, isolated and characterized their degradation products, and established the effect of the thermal treatments on their antioxidant and anticancer properties.

Soy isoflavones were found to be labile to high temperatures simulating commercial sterilization conditions and were degraded with apparent first order kinetics. This is as opposed to the general acceptance that isoflavones are not destroyed by heat but rather are subjected to intra-conversions between the different forms. A new method to assess isoflavone stability was developed and applied for the first time on biological active compounds using microcalorimetric tests. All isoflavones exhibited a large exothermic peak, indicating that indeed a degradation reaction occur. Genistein was found to have a higher thermal stability as compared with daidzein which was explained by the location of an additional hydroxyl group and by its proximity to the 4-oxo moiety in the genistein.

The relevance of the kinetic studies to real soy products was evaluated by conducting kinetic tests on soy milk. The isoflavone, genistin, in soy milk, was labile to degradation during storage. This should be taken into account in regard to shelf life considerations as the shelf life would be considerably shortened.

Genistin and genistein degradation product was isolated for the first time from both model solutions and soy milk. Using NMR and MS the molecular formula of the degradation product is C17H10O8 and putative chemical structures were postulated. The degradation products showed lower biological activities, as an antioxidant and antiproliferation agents, than genistein. They possess only ~60% of the ability to protect from oxidation and only a 30% antiproliferation effect on cancer cells (PC-3 and MCF-7) as compared with genistein.

This study demonstrated that isoflavones do degrade under commercial sterilization conditions and during storage of soy products. The biological activities, antioxidant and anticancer, were altered as a result of the thermal treatments. These findings should be taken into account when soy products are being presented as health promoting foods with consideration to product processing and shelf life, and will provide a basis for developing food with beneficial quantity and quality of isoflavones.