The Preparation Of Antioxidative Peptides From Zein And Its Relationship Between Structure And Functionality

According to researches at home and abroad, the zein hydrolysate has a good antioxidant activity. In this study, based on the peculiarities of corn protein hydrolysate, such as molecular weight, distribution of molecular weight, polarity and so on, ultrafiltration, gel chromatography and reversed-phase high performance liquid chromatography(RP-HPLC) were utilized to separate and purify the peptides. Then the antioxidant activities of the separated products were analyzed by determining scavenging activities of DPPH radical, ABTS radical and superoxide anion radical to explore the correlation between different components of corn protein hydrolysate and their antioxidant activities from various points of view. It is significant to illustrate antioxidation mechanism of corn peptides, as well as with the practical significant for promoting the application of corn proteins.The preparation method of corn protein hydrolysate, which had a good antioxidant activity, was investigated at first. The results were as follows: To the corn protein hydrolysate, after the decolorization of yellow pigment in lipids by chloroform, the reversed-phase filler, C18, was used to absorb the residues of yellow pigment, which avoided the interference of yellow pigment on the antioxidant of corn peptides. At the same time, this process avoided the pigment interference on the research of the antioxidant activity of peptides. Then the Alkaline protease alcalase was utilized to enzymolysis corn protein (30g/L) under the condition of pH 9.0 and 50℃. After 4 hours enzymolysis(the degree of hydrolysis was 21.7%), the hydrolysate had the strongest antioxidant activities. That was to say, DPPH radical scavenging activity was 35.7%, ABTS radical was 58.0%, superoxide anion radical was 11.1%. Finally molecular weight distribution of the hydrolysate was analyzed by the high performance liquid chromatography. Molecular weight distribute range between 200Da～900Da. The area of peptides was higher than 90%.In order to explore the correlation between different components of corn protein hydrolysate and their antioxidant activities from molecular weight, distribution of molecular weight and hydrophobicity, ultrafiltration, gel chromatography and reversed-phase high performance liquid chromatography(RP-HPLC) were utilized to separate and purify the peptides and then determined their scavenging activities of DPPH radical, ABTS radical and superoxide anion radical. The results were as follows: (1) The antioxidant activities of corn protein hydrolysate had a correlation with its molecular weight. DPPH radical scavenging activity had a striking correlation with its molecular weight. That was, DPPH radical scavenging activity degraded as the molecular weight increased below the range of 5000Da. However, ABTS radical and superoxide anion radical scavenging activities didn't show obvious difference. As molecular weight increased gradually, ABTS radical scavenging activity degraded but superoxide anion radical scavenging activity enhanced. (2) The antioxidant activities of corn protein hydrolysate had a correlation with its hydrophobicity. The hydrolysate was separated by hydrophobic chromatography. As the polarity of eluant degraded, DPPH radical and superoxide anion radical scavenging activity of the gradually eluted components enhanced while ABTS radical scavenging activity strengthened firstly and degraded later, which proved that the lower polarity peptides had the stronger DPPH radical and superoxide anion radical scavenging activities, while the middle polarity peptides had the higher ABTS radical scavenging activity.After ultrafiltration, gel chromatography and hydrophobic chromatography as above mentioned, three pure components could be obtained. They were analyzed by Mass Spectrometer(Water Platform ZMD 4000) and Biolynx Software. There were two determined structures of antioxidant corn peptides was obtained by the help of the sequences of zein in SWISS-PROT database. They were Tyr-Ala and His-Cys-Met-Leu.