| Porous starch is a kind of green and environment-friendly adsorption material,which is mainly used as adsorbent and sustained-release agent to absorb and encapsulate the target material,make up for the defects of the original material and improve its properties.Core materials for preparation of microcapsules;It can also be used as hemostatic agent and drug carrier in medicine.In this paper,sweet potato starch with larger granules was used as raw material to prepare sweet potato porous starch by the co-treatment of glucosidase(AMG),β-amylase(BA)and glucosidase transferase(TG).The damage degree,pore formation,particle size distribution,the change of crystal structure and the rmodynamic properties of porous starch granules were measured by the instrument.The main research results are as follows:1.The optimal conditions for the preparation of porous starch were:1200u/g of glucosidase and 12h of enzymatic hydrolysis;The addition of β-amylase was 18u/g and the enzymatic hydrolysis time was 12h.The added amount of glucoside transferase was 8716u/g,and the enzymatic hydrolysis time was 14h.2.Structural characterization of porous starch(1)The surface of porous starch granules was observed by scanning electron microscopy(SEM).The structure of starch granules was damaged and holes were formed on the surface.(2)Polarizing cross of porous starch granules was not obvious or disappeared through polarizing light microscope(PLM).The greater the amount of glucosyltransferase(TG)was added,the polarizing cross was less obvious,and the black area was larger of the cross,indicating that the crystalline structure of starch was destroyed in the process of enzymatic hydrolysis.(3)According to the analysis of the structure of porous starch and original starch by high performance anion chromatography(HPAEC),the original starch peaked when DP was 12,and the ion chromatogram of porous starch showed acromion peak when DP was 12 or 13,and the peak height decreased obviously.In the process of enzymatic hydrolysis,the proportion of short chains in the branched structure of porous starch gradually increased,while the proportion of medium and long chains was decreased,indicating that compound enzyme broke the a-1,4 glycosidic bond and the long chain was cut into short chains.(4)According to the laser particle size analyzer,the particle size distribution range of porous starch is enlarged.When the original starch particle size is distributed,the porous starch is "thin and tall type",and the porous starch is "short and fat type".With the increase of the enzyme content,the particle size distribution range was different and expanded slowly,and most of the particle size was mostly concentrated in 10～100μm.(5)The pore diameter of the original starch is mostly microporous and mesoporous,while the pore diameter of the porous starch is mostly macroporous;Compared with the original starch,the pore size and pore volume of porous starch increased,and the larger the pore size,the larger the pore volume.(6)The differential scanning calorimeter,according to the results of sweet potato starch gelatinization peak temperature of 66.03℃,the range of porous starch peak temperature is 71～73 ℃,and composite enzyme treatment to lower its endothermic enthalpy value,it shows that the crystallization of the starch granules in the process of enzymatic hydrolysis of area was damaged,leading to lower crystallinity.(7)Sweet potato starch in 2 theta for 15°,17°,18°and 23° has obvious diffraction peak,the crystalline structure of C type,the relative crystallinity is 33.28%,after enzyme treatment,the diffraction peaks of the starch change,it have both C type characteristic peak and V type characteristic peak,the crystal structure changes.When porous starch at 2 theta is 23° and 15°,the characteristics of the diffraction peak intensity is abate,and with the increase of amount of enzyme,weaken the intensity of the diffraction peak is more and more big,and for 23 0 peak gradually disappeared in 2 theta,diffraction peak is becoming more and more gentle,the lowest relative crystallinity of 27.41%.3.Adsorption property of porous starch(1)Natural sweet potato starch,oil absorption rate of 25%,oil absorption rate of porous starch is 2～2.5 times of the original starch,the oil absorption rate is 50～62.5%,and that treated with compound enzyme increases adsorption performance of porous starch of sweet potato,this is due to the porous starch granule surface more holes,specific surface area is larger,it can package more oil,and grease molecules combined in a tightly,so the oil absorption rate of porous starch is higher.(2)The adsorption capacity of sweet potato starch to methylene violet was 5.74mg/g,and that of heavy metal ions Cu2+,Cd2+and Pb2+was 16.37mg/g,41.50mg/g and 45.74mg/g,respectively.The adsorption capacity of porous starch to methylene violet was 2～3 times that of the original starch,and the adsorption capacity of heavy metal ions Cu2+,Cd2+and Pb2+ was about 2.5 times,1.5 times and 1.7 times of that of the original starch,respectively.It shows that porous starch is a good adsorption material for pigment and heavy metal. |
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