The Effect Of Polyphenols On Physicochemical, Nutritional And Structural Properties Of Buckwheat Proteins

The interactions of the polyphenols or other phenolic compounds with proteins are of great importance for the physicochemical and structural properties of plant proteins. Therefore, it is very significant to study the properties of proteins based on the contents of polyphenols, which will be useful for providing the knowledge about the properties of plant storage proteins and protein modification, thus facilitating the utilization of these proteins in nutrition and health food formulations. This thesis was mainly concentrated on the interaction of polyphenols and buckwheat proteins, as well as their structure-activity relationship. The effects of polyphenols contents and dephenolizition on the physicochemical and antioxidant properties were investigated systermatically. The main results were showed as follows:The albumin fraction preferably noncovalently interacted with the polyphenols, though in the BPI case, the major part of the polyphenols was in the protein-bound form. The free SH and SS contents of the globulin was significantly higher than that of the albumin. The protein solubility-pH profile of the globulin was similar to that of BPI, while that of the albumin was completely different, especially at pH 4.0-6.0.The effects of polyphenol removal from common buckwheat seed flours with cold aqueous organic solvents resulted in considerable reduction in its polyphenol contents, especially protein-bound polyphenol contents. The albumin fraction in the BPI, which was rich in the polyphenols was decreased. The dephenolization treatment remarkably increased the formation of SS bond formation, partially at expense of free SH groups. The protein solubility of BPIs with low polyphenol contents at neutral and alkali pH values was higher than that of control with high polyphenol contents. It was also proved that the digestion in vitro was inhibited by polyphenols, especially at alkaline conditions.The dephenolization treatment led to significantly improved hydrolysis of BPI. The hydrolysis resulted in gradual decreases in total and protein-bound polyphenol contents, but increases in free polyphenol contents. The hydrolysis of the globulin fraction was nearly unaffected, while that of the albumin fraction was increased by the polyphenol removal. The ?antioxidant activities, including DPPH·and hydroxyl radical scavenging abilities, reducing power and Fe2+ chelating ability of modified BPIs were to a varying extent dependent on the level of the polyphenols and the degree of hydrolysis (DH).The secondary conformation of the globulin fraction was mainly composed of theα-helices andβ-sheets, especially theβtypes, while in the albumin fraction, theα-helices were the prominent secondary structure. The tertiary conformation of the globulin fraction exhibiting a prominent Trp and/or Tyr structure pattern was more compact or rigid in nature, while that of the albumin was highly flexible. The secondary and tertiary conformation of BPI seemed to be similar with BG. The dephenolization treatment also resulted in distinct changes in secondary and tertiary conformations of the proteins, especially the tertiary conformation.It was confirmed that physicochemical and conformational properties of the proteins were closely related to the extent of interaction between the proteins and the polyphenols.