Effect Of Different Working Mode Of Ultrasound Pretreatment On Enzymatic From Wheat Germ And Evaluating The Activity And Stability Of Hydrolysates

Defatted wheat germ is a byproduct of flour processing, the protein is a good raw material preparation of ACE inhibitory peptides. The extensive studies have found that ultrasound pretreatment can increase the ACE inhibitory activity of wheat germ enzyme products significantly.The effects of different working mode of ultrasound on the degree of enzymatic hydrolysis and ACE inhibitory activity of defatted wheat germ were studied under the same condition. And the ultrasound pretreatment technology for defatted wheat germ and enzymatic hydrolysis of defatted wheat germ were optimized. The impacts of ultrasound pretreatment on structure of wheat germ protein were studied by the methods of ultraviolet spectrometry and the changing content of thiol group and two sulfur bond. Meanwhile, it has investigated whether there is a corresponding relationship between the changing structure of wheat germ protein and ACE inhibitory activity of the enzymatic hydrolysate after ultrasonic pretreatment. The ACE-inhibitory peptides from defatted wheat germ were tested in vitro to determine stability.The main research are concluded as follows:(1) In order to study the effects of different working mode of ultrasound on the degree of enzymatic hydrolysis and ACE inhibitory activity of defatted wheat germ,five kinds of working mode of ultrasound, energy aggregation counter flow single-frequency ultrasound, energy aggregation counter flow dual-frequency ultrasound, pulsed and sweeping frequency ultrasound, divergence triple-frequency ultrasound and opposite-site dual-frequency ultrasound were used to pretreat defatted wheat germ under the ultrasonic power per unit volume of 40 W/L.The results illustrated that different working mode of ultrasound pretreatment had no significant effect on the degree of hydrolysis but can increase the ACE inhibitory activity of enzyme products significantly. The maximum ACE inhibitory activity increase rate is8.76%,which is 2.92 times of the minimum of 3%.The best ultrasonic working mode is 40 kHz / 28 kHz pulse plate dual-frequency ultrasound.(2) On basis of optimum working mode of ultrasound, the single factor experiments were conducted, along with the index of the degree of enzymatic hydrolysis and ACE inhibitory activity, so as to optimize the pretreatment on enzymatic preparation of ACE-inhibitory peptides from defatted wheat germ. The results showed the best technical condition of ultrasonic pretreatment and enzymatichydrolysis: ultrasonic power per unit volume of 60 W/L, ultrasound time of 70 min,ultrasonic initial temperature at 60 ℃, the substrate concentration 7%.The IC50 of enzymatic hydrolysates value could drop to 2.483 mg/mL. The percentage of IC50 decreased by 5.8% compared to the control group. Moreover, it displayed that the amino acids and hydrophobic amino acid were enhanced moderately compared with control group after ultrasonic pretreatment of the hydrolyzed wheat germ.(3) The ultraviolet spectrometry of defatted wheat germ pretreated by ultrasound and the changing content of thiol group and two sulfur bond have been studied. By comparative analysis on ultrasonic power, ultrasonic time, ultrasonic per unit volume,substrate concentration,ultraviolet absorption spectrum, thiol and disulfide bond content and its corresponding ACE inhibition, it showed that the change of the ultraviolet absorption spectrum was concerned with the rise of ACE inhibition rate of enzymolysis impacted by ultrasonic wave. The change of thiol and disulfide bond content illustrated that ultrasound could shift the structure of wheat germ protein, but can’t fully explain the changes were related with the change of ACE inhibition rate of enzymolysis.(4) After determining the bioactivity of polysaccharide from the enzyme products of wheat germ, it is found that the polysaccharide in enzyme products from defatted wheat germ could lower blood pressure and has antioxidant effect. Moreover, it is also confirmed that the enzyme products from defatted wheat germ have antioxidant effect.The vitro stability test on enzyme products from defatted wheat germ showed that enzyme products had considerable tolerance to thermal,acid and intestinal digestion.