Conjugation of the glutelin hydrolysates-glucosamine by transglutaminase and functional properties and antioxidant activity of the products.

A novel mixture of glycopeptides was prepared from corn glutelin and glucosamine (GlcN). The functional properties and antioxidative activities of this mixture were investigated. Corn glutelin was limited hydrolyzed by Alcalase, and then its hydrolysates were glycosylated with GlcN by transglutaminase (TGase) to modify its main and side chain, respectively. Under the optimized conditions, the content of GlcN conjugated to peptides was 81.98 ± 1.98 mg/g glutelin peptides. According to electrospray ionization mass spectrometry (ESI-MS) analysis, there are two types of glycopeptides in the mixture, TGase and non-enzymatic glycated counterparts. Compared with original glutelin, the glycosylated glutelin hydrolysates exhibited better solubility in the pH range of 2-11 and other functional properties except foaming stability. Meanwhile, it is more easily digested by pepsin and trypsin, and possessed excellent antioxidative activities. It also exhibited cytoprotective effects and intracellular ROS scavenging activities in LO2 cells subjected to oxidative stress by oxidation with ethanol solution.

Preparation of antioxidative corn protein hydrolysates, purification and evaluation of three novel corn antioxidant peptides.

Corn gluten meal is a major co-product of corn wet milling. Corn gluten meal was hydrolyzed with Alcalase, Flavourzyme, Alcalase+Flavourzyme and Flavourzyme+Alcalase. At the substrate concentration of 10%, corn protein hydrolysate catalyzed by Alcalase had a degree of hydrolysis of 17.83%, which was higher than that by Flavourzyme (3.65%). The hydrolysate catalyzed by Alcalase+Flavourzyme exhibited better antioxidant activities and was further purified. Three novel antioxidant peptides were purified by a series of chromatographic techniques. Sequences of the three peptides were identified as Cys-Ser-Gln-Ala-Pro-Leu-Ala, Tyr-Pro-Lys-Leu-Ala-Pro-Asn-Glu and Tyr-Pro-Gln-Leu-Leu-Pro-Asn-Glu, respectively. Among the three peptides, Cys-Ser-Gln-Ala-Pro-Leu-Ala exhibited good reducing power and excellent scavenging capacities for DPPH radical and superoxide anion radical, with IC50 values of 0.116 and 0.39mg/ml, respectively. The results from our study indicate antioxidant potency of corn protein hydrolysates and peptides separated from corn gluten meal and can provide basic understanding for the application of corn protein hydrolysates as natural antioxidants.

Production of hydrolysate with antioxidative activity by enzymatic hydrolysis of extruded corn gluten.

Hydrolysate of extruded corn gluten with higher solubility and antioxidative property was prepared. Extrusion and starch removal of corn gluten were applied as pretreatment before enzymatic hydrolysis by Alcalase. The amylase hydrolysis of starch at 70 degrees C for 3 h resulted in the removal of the starch from the extruded corn gluten. The best hydrolysis results can be obtained by conducting the hydrolysis at 60 degrees C with water addition 20 g/g protein, enzyme addition 0.048 Ansen units/g protein, pH 8.5, and 120 min. Degree of hydrolysis of extruded and nonextruded corn gluten reached 39.54 and 31.16%, respectively, under the optimal condition. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the optimal hydrolysate revealed that proteolysis of extruded corn gluten was more extensive than proteolysis of its counterpart which was not subjected to extrusion. The molecular weight of the peptides in the optimal hydrolysate was mainly over 3,710-660 Da as determined by gel filtration chromatography. The hydrolysates displayed good solubility and antioxidative activity. The separation profile of the hydrolysate on an ion exchange chromatography of Q-Sepharose Fast Flow showed that many kinds of peptides had antioxidative effect. A new peptide with antioxidative activity was purified, and its amino acid sequence was Phe-Pro-Leu-Glu-Met-Met-Pro-Phe, which was identified by Q-TOF2 mass spectrometry.