Abstract: Heat moisture treatment was imposed on three kinds of Coix seeds (big Coix seed (BCS), small Coix seed (SCS) and translucent Coix seed (TCS)) to explore the water and heat barrier properties of non-starch components. For this purpose, heat moisture-treated (HMT) Coix seed starches were prepared, and scanning electron microscopy, optical microscope, laser particle analyzer, X-ray diffraction, infrared spectrometry and differential scanning calorimetry were used to explore the impact of HMT of Coix seeds on the morphology, size, structure and thermal properties of starch. The results indicated that HMT caused damage to starch granule surface, increased stomatal size, and weakened birefringence. Meanwhile, the double helix structure and the crystalline and amorphous region were broken, the interaction of starch with itself, and with protein and lipid was reinforced, and the starch molecules were reordered to different degrees. As a result, HMT increased the gelatinization temperature of the starches, weakened crystal heterogeneity, and decreased the energy required for uncoiling. BCS starch was influenced slightly, while TCS starch, rich in amylose, was affected heavily by HMT. Thus, we can apply Coix seed starch more reasonably according to variations in starch properties after HMT.

Key words: Coix seed, heat-moisture treated Coix seeds, starch, morphology, structure, thermal properties