| Native starch can be modified to overcome its inherent limitations,so as to meet the needs of the industry and improve its additional value.Both ultrasonic and microwave treatments are effective methods for the physical modification of starch,however,there are limited information about dual-modification of starch using these two methods.In this study,three starches with different crystallinity structures,i.e.,maize starch(A-type crystalline polymer),potato starch(type B)and chestnut starch(type C),were selected as raw materials.Single ultrasonic or microwave treatment,and dual-treatment(ultrasonic-microwave and microwave-ultrasonic)were carried out to explore their effect on the physicochemical and functional properties of starches.The effects of the dual-modification sequence on the physicochemical properties of starches were compared.The main results are as follows:(i)After ultrasonic and microwave modification,the total starch content of the three starches decreased due to the degradation of starch.The apparent amylose content of maize starch(except for single ultrasonic treatment)and potato starch decreased,while that of chestnut starch by different treatments increased.In addition,the damaged starch content of the three kinds of starches increased,and that of the ultrasonic-microwave dual modified samples was the highest,indicating that the starch damage was the most serious.(ii)The microstructure observation revealed that compared with single ultrasonic or microwave treatment,ultrasonic-microwave dual treatment caused more serious damage to the surface of the particles,and the birefringence phenomenon was weakened,suggesting that the surface and crystal structure of the starches modified by ultrasonic-microwave were more severely damaged.The particle size analysis implied that the particle size distribution moved to larger particle sizes under the action of ultrasonic and microwave,indicating that ultrasonic and microwave treatment promoted the aggregation of small particles.(iii)Ultrasonic and microwave treatments did not change the crystal forms of the three starches,but the relative crystallinity was mostly decreased(except for the microwave-treated potato starch).The results of thermodynamic analysis showed that the initial temperature(T_o)of the three starches increased,while the enthalpy value(ΔH)appeared different trends.The short-range order of the three starches also showed different changes.The effect of ultrasonic and microwave processing sequence on theΔH value and short-range order of starch was correlated to the starch type.(iv)The solubility,water and oil absorption capacity of maize,potato and chestnut starches were all increased under the treatment of ultrasonic and microwave,and the freeze-thaw stability became better.Among them,chestnut starch had the lowest syneresis,which was more suitable for frozen food.The dual modification sequence had no significant effect on the water and oil absorption capacity of the three starches(P>0.05),while the effects on solubility,swelling power and freeze-thaw stability were correlated to starch types.Correlation analysis showed that the solubility of the three starches was significant negatively correlated with the relative crystallinity(r=–0.763,–0.826,–0.697).(v)The single microwave treatment increased the resistant starch of the maize,potato,and chestnut starches,reduced the in vitro digestibility and the estimated glycemic index(e GI),while the single ultrasonic and dual treatment increased the digestibility of starch.Potato starch was a low-glycemic food among them,and the microwave-modified sample had the lowest e GI(44.00)that could be used to develop low-e GI foods.Correlation analysis showed that the rapidly digestible starch of the maize,potato,and chestnut starches was positively correlated with damaged starch content(r=0.808,0.960,0.979,respectively),and negatively correlated with relative crystallinity(r=–0.564,–0.712,–0.900,respectively). |
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