| Rice cake,as a traditional Chinese characteristic food,is popular among consumers because of its unique taste and flavor.However,rice cakes age seriously in short-term storage,which restricts its industrial development.Although many studies have shown that adding amylase could delay the aging of starchy foods to a certain extent,the application of this method in the industrial production of rice cakes and other starchy foods were seldom due to the complicated enzyme treatment process and many conditions,and the anti-aging effect product quality were unstable.This project changed the use of enzymes by preparing different amylase（α-amylase andβ-amylase）and different degree of enzymatic hydrolysis of waxy rice starch and studied the influence on the aging characteristics and food qualities of rice cakes.The mechanism of enzymatically-hydrolysates of waxy rice starch（EWS）was investigated from the perspective of starch molecular structure and properties.The results provided reference for anti-aging of rice products and expanding the application of amylase and rice starch in food industry.The main results were as follows:The gelatinization characteristics of rice flour,specific volume,texture,sensory evaluation and volatile flavor compounds of rice cakes were applied to study the changes of food qualities of rice cakes by EWS（substitution of 20%）of different enzymatic degree byα-amylase andβ-amylase.The results showed thatαEWS decreased the viscosity of rice flour by 21.30%,whileβEWS decreased by 43.46%.EWS reduced specific volume of rice cakes.When DE value was>20,the specific volume of rice cakes inβEWS-DE22 group were decreased by 36.47%compared with the control group（p<0.05）,which caused the rice cakes to collapse to a certain extent.EWS significantly reduced the hardness and chewiness of rice cakes（p<0.05）,with a decrease of about 50%,and the decrease was greater with the increase of DE value.The decrease ofβEWS group was greater than that ofαEWS group.For sensory evaluation,with the increase of DE value of EWS,the scores of rice cakes increased,for the reason that the sticky rice flour problem was improved,so the overall acceptance of rice cakes were improved.EWS increased the volatile flavor compounds of esters and furans in rice cakes,and improved the flavor to a certain extent.EWS could effectively delay the aging of rice cakes.The aging rate,thermodynamic properties,crystal structure,moisture content and texture of rice cakes during storage period were applied to study the aging characteristics of rice cakes by EWS.The results showed that with the increase of DE value（DE value<20）,the aging rate of rice cakes decreased by82.38%compared with the control group.When DE value was similar,the aging rate of rice cakes inβEWS group was significantly lower than that inαEWS group（p<0.05）,the highest was 61.56%lower（DE20）.EWS increased the initial gelatinization temperature and peak gelatinization temperature of rice cakes,but had no effect on the formation of starch crystal in rice cakes.The water content and texture of rice cakes decreased during storage,while the addition of EWS reduced the change degree of water content,cohesiveness,elasticity and chewiness,which improved the quality deterioration of rice cakes during storage to a certain extent.The water absorption,solubility,swelling power,viscosity,correlation analysis,thermodynamic properties,long range ordered structure,short range ordered structure,particle morphology,water mobility of rice cakes,molecular weight distribution and chain length distribution were applied to explore the reasons for the varying degrees of characteristics of rice cakes.The results showed that with the increasing DE value,the average molecular weight of EWS decreased,the polydispersity coefficient increased,and the difference of molecular structure increased.The short chain ratio was increased from 0.76%to 72.93%（βEWS-DE20）and the A chain ratio and B chain ratio were decreased,which was beneficial to delaying starch retrogradation.The molecular variation and mean chain ofαEWS were larger than that ofβEWS,and the composition ofαEWS was more complex when the DE value changed.With the increase of DE value,the water absorption,swelling power and viscosity of EWS decreased,while the solubility increased,and the gel strength decreased.The breakdown value and setback value decreased,and the short-term retrogradation degree decreased.The solubility ofαEWS-DE20 was 7.86 times of that of original waxy rice starch,and its swelling power was 3.95%of that of original waxy rice starch,and its final viscosity was 7.50 c P.The solubility ofβEWS-DE22 was 6.8 times of that of original waxy rice starch.The swelling power was 9.64%of original waxy rice starch,and the final viscosity was 67.50 c P,indicating that when DE value was too high,it was not conducive to maintaining the gel strength,andα-amylase had greater damage thanβ-amylase.The correlation analysis showed that the hardness,chewiness,elasticity and specific volume of fresh rice cakes were closely related to the physicochemical properties of EWS（p<0.01）.When the viscosity,water absorption and swelling power of EWS were too low and the solubility was too high,the rice cakes would be too soft and difficult to maintain the shape.With the increasing DE value,the gelatinization temperature of EWS increased after 28 days of retrogradation.The highest was 7.04°C higher than that of control.The crystal structure and infrared absorption peak spectrum of EWS were not different from that of waxy rice starch.B-type crystals were formed during the retrogradation process.The degree of retrogradation decreased and the degree ofβEWS was significantly lower thanαEWS（p<0.05）,which was consistent with the retrogradation trend of rice cakes.SEM grain morphology at the same magnification showed that the starch was meshed.EWS reduced the decrease degree of water mobility of rice cakes during storage period,and T22increased with the increase of DE value on the whole,and retained more moisture in semi-bound water state.The water holding capacity ofβEWS was better than αEWS. |
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