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Optimizion of enzymatic hydrolysis of zein to prepare protein hydrolysate with increased antioxidants

Hai-Teng Tao, Yu-Xiao Wang, Wei Liu, Bin Qiu, Li-Na Liu, Ai-Zhen Zong, Min Jia, Tong-Cheng Xu

Background: Protein hydrolysate was prepared with zein recycled from corn gluten meal. It have been reported that zein have the antioxidant activity. Various recycling methods were selected to obtain zein with desirable characteristics, but ignored the antioxidant activity of hydrolysate. No comparisons of different recycling methods of zein or studies on the use of RSM to optimize enzymatic hydrolysis conditions to increase antioxidant activity could be found.

Materials and Methods: The corn gluten meal used in this study was a gift from the Xiwang group in China. Zein was dis-colored from corn gluten meal by alcohol (1:6) under ultrasound (Elmasonic S50R, German) twice for 15 min each time. Zein was extracted through preliminary optimized conditions of 55% ethanol at 38°C for 15 min. The extracted zein was placed in a beaker before use.

Results: The optimum conditions to obtain a high DPPH radical scavenging rate was close to the predicted value (7.523%, 0.0416 mg/mL ascorbate equiv), and they were as follows: an enzyme to substrate level of 1% (w/w), temperature of 40°C, time of one hour, and pH of 8. HPLC detected more than 26 constituents in the zein hydrolysate, and the content of glutamic acid rose at a relatively high degree from 16.8 to 19.1.

Conclusion: The best recycling method for colourless zein with high antioxidant activity was dilutionfreeze- drying. The zein including hydrolysate has potential for applications in functional foods, which would significantly improve the added value.