| Corn gluten meal(CGM) is a byproduct of maize grain after production of starch in food industry or purification of wine industry. It contains appropriate amount of amino acids.However, due to the low antioxidant effect of protein, it is necessary to hydrolyzed it to produce peptides and improve the utilization of bioavailability. Ultrasound and heat pretreatments were used to improve the hydrolysis of corn gluten meal, facilitating the change of its structure, which become larger, and eases attack with enzyme. In this study, comprehensive balance method was used to optimize the preparation of antioxidant peptide in order to improve the utilization of corn gluten meal. The effects and mechanism of ultrasound and heat pretreatments on the enzymolysis and bioavailability of corn gluten meal were studied. The antioxidant mechanism of corn gluten meal hydrolysate(CGMH) in O/W emulsion were also examined.Effects of five experimental parameters, including CGM concentration, pre-treatment time,enzymolysis pH, enzymolysis temperature and enzymolysis time were investigated to discuss the antioxidant of peptides from CGM by an orthogonal design L16(45). The orthogonal design was used to optimize the best condition for antioxidant and the comprehensive balance method was used to analyze the data:( Ⅰ) CGM concentration of 6%, pre-treatment time of 40 min,enzymolysis pH 7.5, enzymolysis temperature of 55°C, and enzymolysis time of 6 h.(II) CGM concentration of 18%, pre-treatment time of 40 min, enzymolysis pH 7.5, enzymolysis temperature of 55°C, enzymolysis time of 24 h. The validated test measured DPPH IC50,molecular weight(200~2500Da) distribution, degree of hydrolysis, residual ratio and antioxidant indicators(hydroxyl radical IC50, superoxide anion IC50, reducing power) and AY(Ala—Tyr)determination. Optimal process were corn gluten meal at 6%, pre-treatment time of 40 min,enzymolysis pH 7.5, enzymolysis temperature of 55°C, enzymolysis time of6 h.When the concentration of corn hydrolysate was 3.33 mg/mL, DPPH radical scavenging rate was 72.74%and half inhibitory concentration(IC50 value) was 2.09 mg/mL. Hydroxyl radical IC50 value of27.03 mg/mL, superoxide anion radical scavenging IC50 value of 39.91 mg/mL, corn oligopeptide absorbance increased with concentration increasing, and the absorbance and mass concentration substantially proportional relationship, degree of hydrolysis of 19.45%, the remaining rate of 49.76%, AY content of 0.48%.Based on ultrasonic and heating changeson the physical and chemical properties of protein,the effects and mechanism action of ultrasonic pretreatment(UP) and heat pretreatment(HP) on enzymolysis of protein were explored. Effects of ultrasonic and heat pretreatment were studied through dynamic model for corn proteolytic digestion. In order to observe the effects of ultrasonic and heat pretreatmentson the structure of corn protein, fluorescence spectroscopy,FTIR spectroscopy, circular dichroism(CD), scanning electron microscopy(SEM) and atomic force microscope(AFM) wereevaluated. Results show that ultrasonic pretreatment, heat pretreatment and heat pretreatment before ultrasonic pretreatment(HPUP) followed by 5 min digestion, the KM value did not significantly reduce. However, in case of ultrasonic pretreatment before heat pretreatment(UPHP) followed by 5 min digestion, KM value was decreased by11.56%. It was evident that the preprocessing of corn gluten meal with ultrasonic pretreatment before heat pretreatment is not able to make the affinity between the enzyme and substrate in a short period. Preprocessing of corn with ultrasonic pretreatment before heating pretreatment makes the affinity of enzyme and substrate in a short period. Ultrasonic pretreatment before heat pretreatment on the enzymatic reaction kinetics is done by changing the affinity of enzyme and substrate.Results of fluorescence spectra, fourier infrared spectrum, circular dichroism, scanning electron microscopy and atomic force microscope under ultrasonic pretreated corn protein before heat pretreatmentpresent porous, loose tissue; and the structure is become conducive andfacilitate the combination of enzyme and protein.Emulsion stability test showed that tannin could improve the stability ofemulsion. Inverted fluorescence microscope shows after joining tannins emulsion,the particles are larger than not join tannins particles. Laser confocal scanning microscope photo shows that under the same multiples of join tannins emulsion particles per unit areamore than join the latex particles of tannins. Transmission electron microscopy figure shows that the join of tannins make polypeptide wrapped grease is better. Oxidation test show that corn protein hydrolysate for emulsion had oxidation stability, corn protein oxidation characteristics. Rheological test shows that after 15 days of oxidation, emulsion viscosity did not change. This behavior might be attributed that viscosity of the emulsion tends to be smaller, because the fat in emulsion is completely oxidized in 11 days time, resulting in smaller droplet size emulsion, the surface area becomes smaller, the viscosity becomes smaller. |
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