Soft and Hard Textured Wheat Differ in Starch Properties as Indicated by Trimodal Distribution, Morphology, Thermal and Crystalline Properties

Starch and proteins are major components in the wheat endosperm that affect its end product quality. Between the two textural classes of wheat i.e. hard and soft, starch granules are loosely bound with the lipids and proteins in soft wheat due to higher expression of interfering grain softness proteins. It might have impact on starch granules properties. In this work for the first time the physiochemical and structural properties of different sized starch granules (A-, B- and C-granules) were studied to understand the differences in starches with respect to soft and hard wheat. A-, B- and C-type granules were separated with >95% purity. Average number and proportion of A-, B-, and C-type granules was 18%, 56%, 26% and 76%, 19%, 5% respectively. All had symmetrical birefringence pattern with varied intensity. All displayed typical A-type crystallites. A-type granules also showed V-type crystallinity that is indicative of starch complexes with lipids and proteins. Granules differing in gelatinization temperature (ΔH) and transition temperature (ΔT), showed different enthalpy changes during heating. Substitution analysis indicated differences in relative substitution pattern of different starch granules. Birefringence, percentage crystallinity, transmittance, gelatinization enthalpy and substitution decreased in order of A>B>C being higher in hard wheat than soft wheat. Amylose content decreased in order of A>B>C being higher in soft wheat than hard wheat. Reconstitution experiment showed that starch properties could be manipulated by changing the composition of starch granules. Addition of A-granules to total starch significantly affected its thermal properties. Effect of A-granule addition was higher than B- and C-granules. Transmittance of the starch granules paste showed that starch granules of hard wheat formed clear paste. These results suggested that in addition to differences in protein concentration, hard and soft wheat lines have differences in starch composition also.淀粉与蛋白质是影响小麦胚乳（wheat endosperm）最终产品品质的主要组分。在硬麦与软麦两类质构小麦中，由于干扰籽粒软度蛋白（interfering grain softness proteins）的高表达，软麦内的淀粉颗粒（starch granules）与脂质、蛋白质结合更为松散，该现象可能会对淀粉颗粒的特性产生影响。 本研究首次针对不同粒径的A型、B型及C型淀粉颗粒（A-, B- and C-granules）的理化与结构特性展开探究，以解析软硬麦来源淀粉的差异。实验中，三类淀粉颗粒的分离纯度均大于95%。A型、B型、C型颗粒的平均占比分别为18%、56%、26%，以及76%、19%、5%。 所有颗粒均呈现对称双折射图案，仅强度存在差异；且所有颗粒均表现出典型的A型微晶（A-type crystallites）结构，其中A型颗粒还具备V型结晶度（V-type crystallinity）特征，这是淀粉与脂质、蛋白质形成复合物的标志性表现。 不同颗粒的糊化焓（ΔH）与转变温度（ΔT）存在差异，加热过程中的焓变也各不相同。取代分析结果表明，不同淀粉颗粒的相对取代模式存在区别。 双折射强度、结晶度百分比、透光率、糊化焓与取代程度均遵循A>B>C的顺序，且硬麦中的相关指标均高于软麦；而直链淀粉含量（amylose content）同样遵循A>B>C的顺序，但软麦中的直链淀粉含量整体高于硬麦。 重组实验（reconstitution experiment）结果表明，通过调整淀粉颗粒的组成即可调控淀粉的特性。向总淀粉中添加A型颗粒会显著改变其热性质，且A型颗粒的影响效果优于B型与C型颗粒。通过对淀粉颗粒糊的透光率测试发现，硬麦来源的淀粉颗粒可形成透明度更高的糊状物。 上述结果表明，除蛋白质浓度存在差异外，软硬麦品系在淀粉组成上同样存在区别。