Evaluation of antioxidant activities of zein protein fractions.

Zein protein was extracted from the by-product corn gluten meal. The obtained zein protein was 1st hydrolyzed by 4 different proteases. The antioxidant activities of the hydrolysates or peptides were evaluated by free radical scavenging activity, metal ion chelating activity, and lipid peroxidation inhibitory capacity. Among hydrolysates produced, alkaline protease hydrolysates exhibited the highest antioxidant activity. A regression model was established by uniform design to optimize the alkaline protease hydrolysis conditions. The hydrolysates with molecular weight < 3 kDa obtained from ultrafiltration showed the highest antioxidant activities in all relevant assays. The hydrolysates with molecular weight <3 kDa were subsequently purified by gel filtration chromatography, and fraction F3 exhibited the highest antioxidant activities. Two peptides were identified from fraction F3 using LC-ESI-Q-TOF MS/MS as Pro-Phe (263.13 Da) and Leu-Pro-Phe (375.46 Da). These peptides exhibited good free radical scavenging activity and lipid peroxidation inhibitory effect. The results clearly indicated that zein protein fractions are good sources for the development of natural antioxidants for the food industry.