Pasting,Rheological Properties And The Relationship With Gel Properties Of Eight Kinds Of Starch

Pasting,rheological and gel properties of starch have a great relationship with the processing and quality of starch-based products.Currently,no research has achieved continuous testing of gelatinization,rheological and gel properties of tuber,legume and cereal starch,meanwhile,no analysis of the correlation between pasting,rheological properties with and gel properties was conducted.Setting different processing temperatures(95/80/65?)in gelatinization program,the pasting and rheological properties of eight kinds of starches(potato,sweet potato,cassava,mung bean,pea,buckwheat,wheat and corn starch)were studied,then the gel properties of starch after cooling was determined to achieve continuous detection of these three properties,and the correlation between pasting,rheological properties and gel properties were analyzed.The gelatinization properties of tuber,legume and cereal starch at the concentration of 5% and 10% were studied by dynamic rheometer.The results showed that the gelatinization temperature of wheat starch was the highest and the lowest was potato and mung bean starches at the concentration of 5%,while that of corn starch was the highest and the lowest ware potato and wheat starch at the concentration of 10%.The peak viscosity,trough viscosity and final viscosity of starch increased with the increasing of concentration(5%?10%),and the cereal starch increased mostly,followed by tuber and legume starches.When the concentration doubled(5%?10%),the peak viscosity,trough viscosity and final viscosity of starch increased by 2-15,1-10 and 2-13 times,respectively.The peak viscosity,trough viscosity and final viscosity of potato starch was the highest and the lowest was wheat starch at the concentration of 5%,while that of potato starch was the highest and the lowest was buckwheat starch at the concentration of 10%.The highest processing temperature in gelatinization program could affect the gelatinization of starch,and some starch granules could not be gelatinized completely at 80?and 65?.The dynamic rheological properties of starch showed that the elastic modulus and viscosity modulus of starch increased with the increasing of concentration(5%?10%),and the increase extent of cereal starch was the largest.At 95? and the termination point(50?),the elastic modulus of corn starch was the largest and the lowest was cassava starch at the concentration of 5%,while that of pea starch was the highest and the lowest was cassava starch at the concentration of 10%.The thermal stability of tuber starch was the best,and the changing tendency of its elastic modulus and viscosity modulus were more gentle(50?95?50?).At the temperature rising stage of dynamic rheology,starch which was not fully gelatinized in the gelatinization program had a significant increase in elastic and viscous modulus when the temperature reached 65 or 80?.The static rheological properties showed that the consistency coefficient and the hysteresis loop area of starch increased with the increasing of concentration(5%?10%),and the fluid index decreased with the increasing of concentration.The higher the consistency coefficient was,the higher the viscosity of starch was.The consistency coefficient of mung bean starch was the largest and the smallest was wheat starch at the concentration of 5%,while that of wheat starch was the largest and the smallest was cassava starch at the concentration of 10%.The larger the hysteresis loop area was,the worse the shear stability of starch was,the hysteresis loop area of potato starch was the largest and the lowest was pea starch at the concentration of 5%,while that of pea starch was the largest and the lowest was cassava starch at the concentration of 10%.The higher the fluid index was,the nearer to the Newton fluid the starch paste was.The fluid index of wheat starch was largest and the lowest was corn starch at the concentration of 5%,while that of pea starch was the largest and the smallest was corn starch at the concentration of 10%.In the gelatinization program,the highest processing temperature decreased(95/80/65 ?),the consistency coefficient increased and hysteresis loop area of starch paste decreased.The textural properties of tuber,legume and cereal starch gel(5%,10%)were determined by texture analyzer.The hardness and gumminess increased with the increasing of concentration(5%?10%),which increased 1.5-5,1.5-12 times respectively when the concentration doubled.The increase extent of legume starch was the largest,indicating the highest hardness and gumminess and the strongest gel-forming ability.The hardness and gumminess of mung bean starch gel was the largest and the lowest was cassava starch at the concentration of 5%;while that of pea starch was largest and the lowest was cassava starch at the concentration of 10%.The influence of the highest processing temperature in the gelatinization program on the textural properties was no regular.The microstructure of starch gel after freeze-drying was observed by scanning electron microscope.All starch gels with different temperature showed network structure like spongy,the sizes of the network holes were 30-470 ?m,and the depth and thickness of the network holes were 1-20 ?m.The mesh size decreased and the hole depth increased when the concentration doubled(5%?10%).Potato,sweet potato,green beans and corn starch formed a more perfect network,which showed the uniform pore distribution,density pore and complete hole-wall,and that of cassava,peas,wheat and buckwheat starch had a loose network structure,whose hole wall had small pieces and layer structure.The freeze-thaw stability test showed that the freeze-thaw stability of potato starch was the worst,followed by legume and cereal starch.Correlation analysis between pasting,rheological properties and gel properties showed that gelatinization temperature and fluid index of starch paste were positively associated with the hardness and gumminess of starch gel;the peak viscosity,trough viscosity,final viscosity,consistency coefficient and area of hysteresis loop were positively associated with the hardness and gumminess of starch gel.The above results indicated that choosing starch with lower gelatinization temperature and fluid index or higher peak viscosity,trough viscosity and final viscosity,or higher consistency coefficient and area of hysteresis loop,can formed starch gel with high hardness and gumminess.