Analysis Of Starch Synthesis Gene Expression,starch Molecular Structure And Extrusion Characteristics Of Maize With Different Amylose Content

High-amylose starch is a kind of starch in which the amylose content is more than 50%.High-amylose starch has a bright applicant prospect in medical,food and material industries,due to its special physicochemical characteristics.Based on the maize inbreds and hybrids with different amylose contents,this study investigated the expression levels of starch synthesis genes of high-amylose maize grains during the filling stage,the molecular structures of starches with different amylose contents,and the properties of the extrudate from high-amylose maize grains.1.As the AC increased in high-amylose starches from 27.4% to 62.0%,the average chain length(ACL)of the amylose(Am)decreased from a degree of polymerization(DP)of ~1013 to ~800.The ACLs of Am in high-amylose starches were lower than that in normal maize starch.The proportion of long Am chains in the Am decreased while that of short and intermediate Am chains increased.The ACL of amylopectin(Ap)increased from a DP of ~28 to ~31,and the degree of branching(DB)of Ap declined from 3.6% to 3.2%.The proportions of Fb2 and Fb3 chains in Ap increased,while the proportions of Fa and Fb1 decreased.The increased Am contents in high-amylose maize starches were mainly due to the increased amounts of intermediate Am chains(DP 141-720),and the decreased ACL of Am with increasing Am content was mainly due to the decreasing proportion of long Am chains and the decreasing ACL of the intermediate Am chains.The increased ACL of Ap was mainly due to the increased ACLs and proportions of Fb2 and Fb3 chains in the Ap.2.In the high-amylose maize inbreds,namely,H1(45.2% AAC),H2(55.4% AAC)and H3(62.0% AAC),the expression level of wx increased as the AAC increased.The expression levels of ss1,du1,sbe1 and ae1 followed trends similar to what was observed for wx.The expression levels of sbe1 and ae1 in H2 and H3 were higher than their levels in B73.The expression level of sugary2 in H1 was higher than those in H2 and H3.The expression levels of iso2 and zpu1 in high-amylose maize inbreds were generally higher than those in B73.The high-amylose maize inbreds in this study are expected to be wx mutants,which have higher GBSSI activity than B73.SSIIa and SSIIIa likely contribute to the synthesis of intermediate and long Ap chains,respectively.SBEs likely play a key role in the branching and length modulation of Am,and they might preferentially generate long Am chains.The higher expression levels of DBEs should contribute to the lower DB of Ap in high-amylose maize inbreds.3.Compared to extrudate from normal corn grits(NCG),high-amylose corn grits(HACG)extrudate has higher contents of protein,lipid,fiber,amino acids and resistant starch(RS),but lower content of total starch.HACG extrudate has smoother surface,below which the inner air cells are smaller and more compact.HACG extrudate has lower buck density(BD),radial expansion index(REI)and water solubility index(WSI),but higher specific length(SL)and water absorption index(WSI).Frangibility and cohesiveness in HACG extrudate are higher than in NCG extrudate,but no significant difference was found in hardness,springiness and chewiness.Compared to NCG extrudate,HACG extrudate has better sensory properties,like better overall taste,lower coarseness and lower adhesiveness(to teeth).