Effect Of Extrusion On Multi-scalestructure And Physicochemical Properties Ofseveral Starches

Extrusion is a common,green and sustainable physical modification method.However,the research on starch structure and physical and chemical properties is not systematic enough,which limits the application of extrusion in starch modification.In this study,the starch-water blend was used as the raw material,and the starch was physically modified by twin-screw extrusion.Modern analysis and detection technology is used to study the changes of starch's molecular chain structure,aggregate structure and physical and chemical properties.The effects of moisture content and screw speed on the structure and properties of maize starch were studied.Then the effects of extrusion parameters and starch types on in vitro digestion characteristics were investigated,and the reasons for the differences were analyzed.Using maize starch(MS)as raw material,the effect of material moisture content(30%-50%)on the properties and structure of extrudates was studied.The extrusion treatment improves the water solubility index(WSI)and water absorption index(WAI)of MS,reduces the gelatinization characteristic value and the storage modulus(G?)and loss modulus(G??)of the gel.Extrusion treatment reduces starch molecular weight,relative crystallinity(Rc)and double helix order.With the increase of moisture content(30%?50%),the molecular weight,Rc,double helix order(DO)and the distribution ratio of long chain(B₂chain+B₃chain)of EMS samples increased first and then decreased.The content of 40%is its inflection point.According to the above test results,the moisture content of the material was determined to be 40%,and the influence of the extrusion screw speed on the structure and properties of maize starch was studied.Thermogravimetric analysis(TGA)showed that the temperature of the maximum mass loss rate(T_m)decreased from 322.56?to312.70?after extrusion treatment,and the weight loss rate increased from 71.31%to75.27%.At a screw speed of 5 Hz,MS has the lowest degree of degradation and the highest degree of gelatinization.The EMS-5 sample has a higher molecular weight,while Rc and double helix have the lowest degree of order.At the screw speed of 45 Hz,the degradation of MS is the greatest,and a large amount of amylopectin is sheared to produce more linear chains,and the molecular weight is lower.Using maize starch as reference,Pea starch(PS),Cassava starch(CS)and japonica rice starch(JRS)were selected to analyze and compare the differences in structure and gelatinization characteristics of starches from different plant sources.The effects of screw extrusion on different starches were investigated.The order of amylose content was PS>MS>CS>JRS.After extrusion,the amylose content of PS increased to 45.59%,while the amylose content of CS,JRS and MS decreased to 27.81%,24.06%and29.83%,respectively.The distribution ratio of amylopectin chain length of JRS starch was similar to that of MS starch,while the distribution ratio of amylopectin chain length of CS starch and PS starch was slightly different from that of MS starch.The extrusion had an effect on the distribution of amylopectin chain length,and the content of short chain was generally increased,but the effect was not significant.The crystal forms of EMS and EJRS changed from A to A+V,and the relative crystallinity size was EPS>EMS>EJRS>ECS.Among them,the relative crystallinity of CS decreases the most.DSC results show that MS has a higher peak temperature,CS has a higher enthalpy value,and the extruded starch samples have no obvious gelatinization peak.The results of RVA showed that the gelatinization characteristic value of extruded starch was lower than that of natural starch,and the gelatinization characteristic value of CS was the largest before and after extrusion.The reason is that the content of amylose in CS is lower,and the content of A chain in amylopectin is higher.The results of in vitro digestion experiments showed that the extrusion treatment significantly improved the digestibility of MS(P<0.05).When the moisture changes from 30%to 40%,the RDS content is negatively correlated with the moisture content,and the SDS content is positively correlated with the moisture content.When the water content continues to increase to 50%,the correlation is opposite.As the screw speed increases,the shearing force increases,thereby improving the digestibility of starch.In addition,the difference in starch digestibility is closely related to structure.In summary,the extrusion process can effectively change the gelatinization,rheology and digestion properties of starch by changing the molecular chain structure and aggregate structure of starch.By establishing the relationship between the properties and structure of starch before and after extrusion,we can further understand the changes of starch in the process of extrusion,which provides a theoretical basis for the application of extrusion in starch modification.