Effects of Enzymatic Deamidation by Protein-Glutaminase on Structure and Functional Properties of α-Zein

The performance of novel protein-glutaminase (PG) purified from Chryseobacterium proteolyticum on α-zein was investigated. Highly insoluble α-zein was able to be deamidated to the extent of deamidation degree 62% by using 50 mM potassium phosphate (pH 8) containing 11.7% ethanol, at 40 °C for 137 h. Analysis by sodium dodecyl sulfate polyacrylamide−gel electrophoresis showed that deamidated and non-deamidated zeins have different mobilities. Results of circular dichroism spectra revealed the decline in α-helix contents of α-zein by deamidation. Besides, Fourier transform infrared spectroscopy analysis demonstrated alterations in the secondary structure of α-zein by deamidation. The assignment of the amide I region showed a remarkable decrease in antiparallel intermolecular β-sheets (around 1690 cm-1) as an indication of the weakening aggregation ability of the deamidated molecules. Solubility and emulsification properties of α-zein, particularly at pH 7, were remarkably improved after the deamidation by PG. Gas chromatography and peroxide value studies pointed out that deamidated α-zein in powder form exhibited an inferior antioxidative property as compared with the non-deamidated one. Keywords: α-Zein; protein-glutaminase; deamidation; secondary structure; solubility; emulsification; antioxidation