The changes in the chemical and biological properties of native proteins after modifying their side chain groups

Wheat gluten was acetylated with acetic anhydride at different concentrations (0.1, 0.2, 0.4, 1.0, 3.0, and 4.0 ml of anhydride/g protein) in the presence of sodium acetate for 1h at room temperature to give acetylated proteins. Wheat gluten was also deamidated with succinic acid at different concentrations (0.017–0.042-0.066 mol.L–1). Succinic acid added to 10% (w/v) wheat gluten suspension, heated at 121°C for different time intervals (0–15 min) and immediately held in ice water bath for 5 min to stop reaction. Acetylation raised the iso-electric point of wheat gluten from pH 6 for the native gluten to pH 8 in the case of acetylated gluten. The SDS–PAGE of acetylated proteins showed slight increments in the molecular weight distribution. The migration of the protein samples in Urea-PAGE into cathode direction indicated that acetylated wheat gluten was much quicker than the respective native protein indicating higher positive charges on the acetylated gluten. Deamidation decreased the iso-electric point of wheat gluten from pH 6 for the native gluten to pH 4 in the case of deamidated gluten. The migration of the protein samples in Urea-PAGE into cathode direction indicated that deamidated wheat gluten was much slower than the respective native protein indicating higher negative charges on the deamidated gluten. Applying acetylated and deamidated gluten at 20 μg/ml to Petri dishes containing nutrient agar infected with pathogenic Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) did not show any inhibition zone.