Heat stress (HS) is a major environmental constraint in sustaining global waxy maize production under future climate condition. Starch physicochemical properties under 5‐day (HS5) and 10‐day (HS10) postsilking HS were investigated using two waxy maize hybrids (Suyunuo5 and Yunuo7) as materials. Ambient and high temperatures were 28°C/20℃ and 35°C/27℃, respectively. Starch granules were enlarged and exhibited additional pitting or cellular structures, increased amylopectin chain length, increased relative crystallinity, and increased 1047/1022 cm−1 ratio under HS. This finding indicated the stable and ordered structure of starch granules, especially under HS10. Pasting viscosities of Yunuo7 reduced by HS, and the change was the same under both HS5 and HS10. Peak viscosity of Suyunuo5 was unaffected and breakdown viscosity increased with HS5 although both characteristics decreased with HS10. HS increased gelatinization temperatures and retrogradation percentage. Results showed that HS enlarges starch granules with stable structure, reduces starch viscosities, and increases retrograde tendency, with severe detrimental effect under long HS durations.
Sweet-waxy maize is a special type of maize with recessive mutations of waxy gene and a gene disturbed sugar-starch transition, and its starch is composed of nearly pure amylopectin. The starch physicochemical properties of four inbred lines and six hybrids of sweet-waxy maize are studied. The starch granules are irregular and large in hybrids and oval and small in inbred lines. The chain length, molecular weight, and crystallinity are significantly different among the samples. However, no distinct difference is observed between hybrids and inbred lines. The branching degree of hybrids (except THN2000) is significantly higher than that of inbred lines. The pasting, gelatinization, retrogradation temperatures, peak and breakdown viscosities, retrogradation enthalpy, and percentage are lower in inbred lines than in hybrids. By contrast, trough, final, and setback viscosities and gelatinization enthalpy are indistinctly different between the hybrids and inbred lines. Among the six hybrids, HTN2 is suitable to make glutinous food due to its high viscosity, whereas MTN2 may enable the production of food with minimal retrogradation. The high viscosity of JH1501 and the low retrogradation percentage of JSW15525 among the four inbred lines endow different advantages on quality breeding.
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