The Effects Of Repeated/Continuous Heat-moisture Treatments On Structural And Physicochemical Properties Of Different Crystal Types Of Starches

In recent years,the chemical industry of starch as material has developed rapidly,which have become important components of the national economy.However,the original starch has the problems and greatly limits the extensive application of the original starch.Therefore,in order to expand its application range and improve its performance,we modify starch with all kinds of methods.Heat-moisture treatment is the heat treatment process of starch under low moisture content.Generally,the moisture content is between 18% and 35%,and the temperature is relatively high.The effect on starch properties depends on the type,source and treatment condition of starch.Heat-moisture treatment is a potential and environmental-friendly modification method.In this study,three kinds of wheat A,B and whole starch(common wheat,part waxy wheat and waxy wheat),potato starch,red adzuki bean starch and mung bean starch were used as materials to study repeated/continuous heat-moisture treatment of starch granules of different crystal forms.The results of repeated/continuous heat-moisture treatment were compared.The effects of structural properties,physicochemical properties,and enzymolysis properties were compared to explore the impact mechanism.The main results were as follows:(1)Whole wheat starch(common wheat,part waxy wheat and waxy wheat)are round or oval,and the particles are divided into larger A type and smaller B type,and the surface of particles is smooth.Wheat A starch is round or lentil-shaped,and wheat B starch is round or polygonal.Potato starch is oval or olive-shaped,and the surface is smooth,which particles are larger.Red adzuki bean starch is round or oval with a small amount of cracks on the surface.The smaller particles of mung bean starch are round,and the larger particles are oval,and the surface of the particles has a small amount of cracks.After repeated/continuous heat-moisture treatment,the starch granules are destroyed and start to aggregate,as the scallops start to appear.As the time of continuous heat-moisture treatment and the number of repeated heat-moisture treatments increase,the scallops on the surface of the starch granules and the damage degree increases.The aggregates gradually increase.The starch granules after heat-moisture treatment appear hollow in the center,and as the increase of processing time and times,the diameter and depth of the hollow area increase.After repeated/continuous heat-moisture treatment,the polarization crosses disappear,and with the treatment times and processing time increase,the disappeared number of polarization crosses increase gradually.After heat-moisture treatment,the bright fluorescent area and the hilum becomes darker,and the edges and growth rings of starch particles become blurred gradually.The crystal types of three types wheat A,B starch,whole wheat starch and mung bean starch are A type.The crystal type of potato starch is B type.The crystal type of red adzuki bean starch is C type.After repeated/continuous heat-moisture treatment,the crystal types of the three types wheat A,B,whole starch and mung bean starch did not change and remained A type.The crystal type of potato starch changed from B type to C type.The crystal type of red adzuki starch changed from C type to A type.After repeated/continuous heat-moisture treatment,the crystallinity of the three crystal types starches decreased.As the increase of processing time and times,the changing trends of different starches are different.According to the FTIR spectra,the spectra of three types wheat A,B,whole starch and potato starch have a blue-shifted and the spectra of red adzuki bean starch and mung bean starch have a red-shifted after repeated/continuous heat-moisture treatment.After repeated/continuous heat-moisture treatment,there are some influences on starch-iodine-blue,iodine-binding capacity and maximum absorption wavelength of three wheat A,B,whole starch(common wheat,part waxy wheat and waxy wheat),potato starch,red adzuki bean starch and mung bean starch.Meanwhile,compared to the native starch,the freeze-thaw stability of the three crystalline starches deteriorated,the water holding capacity increased,the SDS content gradually increased,the RS content gradually decreased,and the swelling power also decreased at higher temperatures.The peak viscosity,trough viscosity,final viscosity and set back viscosity were significantly lower than those of native starch.(2)The contents of amylose of three untreated wheat A,B and whole starch were as follows: common wheat > part of waxy wheat > waxy wheat,and the relative crystallinity was: common wheat < part of waxy wheat < wheat wheat.The various physicochemical and digestive properties of three wheat starches are closely related to their amylose content and crystallinity.The higher of amylose content,the higher of starch-iodine-blue,the higher of solubility,the lower of swelling power,and the lower of peak viscosity.In the meantime,the higher of starch crystallinity,the smaller of water holding capacity and water leaching rate,the greater of enthalpy,and the higher of resistant starch content.Compared with continuous heat-moisture treatment,repeated heat-moisture treatment has a more significant effect on the structural properties,physicochemical properties and enzymatic hydrolysis properties of different crystal types starches.This may due to the existence of a cooling process in the repeated heat-moisture treatment that does not occur in the continuous heat-moisture treatment.In this process,the structure of the starch granules becomes more stable and the link between the recombinant amylose and amylopectin,amylose and amylose are strengthened.In addition,during the cooling process,the water molecules in the starch are redistributed,laying the foundation for structural changes in the next cycle.