Alternating Electric Field Enhancement Of α-Amylase-catalyzed Hydrolysis Of Corn Starch

Starch,which is one of the most abundant macromolecular resources in nature,is widely used in food,textile,medicine and other fields due to its low cost,easy availability,and renewability.However,native starch has some disadvantages such as extremely low solublity in cold water,poor emulsifying ability,poor mechanical stability,low storage stability and easily aging property.Therefore,starch typically needs to be degraded into high value-added products such as amylose,glucose syrup and fructose syrup by enzymatic or chemical methods to improvethe functional properties.Compared with chemical methods,enzymatic modification is environmental friendly and efficient.However,there are some restricts for the industrial applications of enzymatic modification,due to the poor binding ability of amylase to native starch granulesthe inactivation of amylase,and the strict environmental requirements.Electric field treatment can induce the exposure of active groups of enzyme molecules,increase the affinity of enzyme to raw starch,and thus exhibiting as a green,efficient and continuous treatment technique.Therefore,in this paper,the effect of alternating electric field on the efficiency of amylase-catalyzed hydrolysis was studied by using corn starch as substrate and alpha-amylase as catalyst,the mechanism of electric field enhancement of starch enzymatic hydrolysis was revealed by exploring the changes in amylase activity and starch structure during electric field treatment;and a new technology with low energy consumption and high production efficiency was established.The detailed contents are as follows:1.The effects of electric field on the enzymatic hydrolysis efficiency,structure and physicochemical properties of hydrolyzed starches were investigated.The results showed that electric voltage and reaction temperature significantly improved the hydrolysis efficiency of corn starch,whereas frequency,ion species and ion concentration had no obvious effect on the hydrolysis efficiency.For example,the efficiency increased significantly from 9.81%to 30.05%.when the voltage was increased from 0 V to 25 V,while the efficiency remained between 11.43%and 11.81%when the frequency was increased from 0 Hz to 350 Hz.With hydrolysis,the surface of starch granules became rough and some pores and cracks appeared;the size of starch granules gradually decreased,the amorphous and crystalline areas inside starch granules were destroyed;the gelatinization temperature and enthalpy were decreased.Meanwhile,the water and oil absorption of hydrolyzed starcheswere increased by 2.34 and 4.69 times,expending the possible applications as adsorbents and embedding materials.2.The effect of electric field on the enzymatic hydrolysis of corn starch was studied by investigating the activity and structure characteristics of α-amylase during electric field treatment.The results showed that the electric voltage,frequency,treatment temperature,and treatment time significantly affected α-amylase activity.For example,as the voltage increased from 0 to 25 V,the enzyme activityinitially increased and then decreased.At a voltage of 5 V and a frequency of 150 Hz,the activity of α-amylase was the highest,23.28%higher than that of the original enzyme.After electric field treatment,the optimum temperature and pH value of enzyme remained unchanged.However,the optimum reaction range was widened,the thermal stability was improved,the activity loss was delayed,and the affinity between enzyme and substrate molecule was increased.The change of enzyme activity was significantly related to the change of its conformation.After electric field treatment,the primary structure of alpha-amylase had little change,but the secondary structure tended to be ordered.The content of β-coil and random crimp decreased by 14.74%and 12.86%,respectively.Moreover,more hydrophobic amino acids such as tryptophan were exposed in the tertiary conformation of enzyme protein.Overall,the variation trend of enzyme activity was different from that of enzyme efficiency under electric field,which indicated that the change of enzyme activity was not the only factor of the enhancement of amylases under electric field.3.Analyze the change characteristics of corn starch structure and physical and chemical properties under the action of medium and strong electric field,and reveal the mechanism of the change of starch structure and properties on the electric field intensifying the enzymatic hydrolysis of corn starch.The results show that the surface of the corn starch particles treated by the alternating electric field changes from smooth and flat to rough and concave.When the voltage increases to 25 V,they even break into small particles,and the volume average particle size also decreases,compared with the original one.Starch decreased by 28.11%.The crystalline region of starch molecules is damaged to a certain extent,resulting in a decrease in the proportion of this region,and the hydrogen bond between the crystalline phase and the amorphous phase is broken.The complete gelatinization temperature of corn starch was reduced by 11.49%,and the enthalpy value was reduced by 52.11%.At the same time,the peak viscosity of corn starch also decreased sharply with the increase of the electric field treatment intensity,reducing by 51.68%.Therefore,the changes of starch structure and physicochemical properties under the action of electric field are significantly positively correlated with the enzymolysis efficiency,which is a key factor in determining the enhancement of enzymatic hydrolysis of starch by electric field.