Optimization of Transglutaminase Cross-linking of Pumpkin Oil Cake Globulin; Improvement of the Solubility and Gelation Properties

Enzymatic cross-linking of hull-less pumpkin oil cake globulin was studied using microbial transglutaminase. Response surface methodology was employed to study the effect of enzyme/substrate ratio, temperature, and reaction time on protein cross-linking reaction, measured by degree of polymerization (DP) as a response. The second-order polynomial model showed good fit with the experimental data since the coefficient of determination was R 2 = 0.9297. Reaction time of 39.2 min, E/S ratio of 1/4.9 ( w / w ) and temperature of 28 °C were found to be optimal conditions to achieve the highest value of DP (69%). The solubility and gelation properties of the cross-linked proteins with different values of DP were assessed for improvement. The solubility of polymerized proteins was increased over the pH range 5.0–8.0 and affected with increase of DP, at each pH value studied. The highest solubility was achieved at DP of 60%, at pH 7.0 and was 24-fold higher than solubility of unmodified protein. Gelation properties of cross-linked protein were also improved and the highest decrease of least gelation concentration was achieved at pH 9.0.