Fully understanding the structures and properties of starches with different amylose contents is important to agriculture and food industries. Structural and functional characteristics of three Japonica rice starches differing in amylose content (<0.5%, 18.8%, and 33.3% for waxy, normal, and high-amylose varieties, respectively) were investigated using a range of characterization methods. As amylose content increased, the weight-average molecular weight, short-range order, relative crystallinity, and lamellar peak intensity of starch decreased. High-amylose starch contained a lower proportion of A chains than waxy and normal starches. High-amylose starch displayed a C-type crystalline structure, different from the A-type crystalline structure of waxy and normal starches. Compared with waxy and normal starches, high-amylose starch exhibited higher granule size (volume-average diameter), pasting temperature and higher resistant starch content, but lower peak viscosity, breakdown viscosity, swelling power, and rapidly digestible starch content. These results can provide reference for the exploitation of Japonica rice starches.

Starches rich in amylose are promising functional ingredients for calory-reduced foods. In this research, a high-amylose Japonica rice starch (amylose content 33.3%) was esterified with octenyl succinic anhydride (OSA) to improve the functional properties. The OSA-modified derivatives were evaluated for structure and functional properties, with OSA-modified normal Japonica rice starch (amylose content 18.8%) used as control. Fourier transform infrared spectra confirmed the introduction of OSA groups to starch. OSA modification made little change to morphology and particle size of high-amylose starch, but decreased the relative crystallinity and pasting temperature and increased the pasting viscosity, swelling power, emulsifying stability, and resistant starch (RS) content. The changes of properties were related to the degree of substitution (DS). Typically, OSA-modified high-amylose starch at DS of 0.0285 shows polyhedral-shape granules, with a volume-average particle diameter of 8.87 μm, peak viscosity of 5730 cp, and RS content of 35.45%. OSA-modified high-amylose starch had greater peak viscosity and RS content and lower swelling power than OSA-modified normal starch of similar DS, but the two kinds of derivatives did not have a significant difference in emulsifying stability. The OSA-modified high-amylose Japonica rice starch could be used as an emulsifier, thickener, and fat replacer in food systems.

Pasting, cooking, and digestible properties of Japonica rice with different amylose contents were investigated. Low-, medium-, and high-amylose Japonica rice (waxy, 18.8% amylose content, and 33.3% amylose content) were cooked and evaluated for water absorption, volume expansion, molecular mobility, microstructure, crystalline structure, and starch digestibility. The results showed that high-amylose rice had lower peak viscosity but higher pasting temperature and final viscosity than low- and medium-amylose rice. After cooking, high-amylose rice showed slightly higher water absorption ratio but lower volume expansion ratio than the other two rice varieties. Water was more evenly distributed in cooked low- and medium-amylose rice than in cooked high-amylose rice. After cooking, starch in low- and medium-amylose rice kernels almost lost the entire crystalline structure, but starch of cooked high-amylose rice still exhibited strong V-type crystallinity. Cooked high-amylose rice contained higher content of resistant starch than cooked rice of other two varieties.

Five experimental storage conditions were designed to study the effect of storage temperature on paddy rice. Three of the conditions were designed with varied order of temperature but with the same overall exposure. The five conditions were: (i) 15°C for 12 months (low-temperature condition, LC); (ii) 30°C for 12 months (high-temperature condition, HC); (iii) 15°C for 6 months followed by 30°C for an additional 6 months (low–high-temperature, LH); (iv) 30°C for 6 months followed by 15°C for an additional 6 months (high–low-temperature, HL); and (v) alternating 2-month intervals at 15°C and at 30°C for a total of 12 months (alternating low–high-temperature, ALH). The resultant quality attributes of the stored rice samples were measured and compared at intervals over the 12 months. For all samples, fat acidity increased during storage, while germ cell volume and cell gap decreased. The changes were greater after exposure to high temperature than after exposure to low temperature. However, the overall results for the samples stored at varied-temperature conditions showed only slight differences in fat acidity, as well as in germ cell volume and cell gap. In addition, the overall results for these samples yielded only slight differences in polyphenol oxidase activity, peroxidase activity, pasting parameters, and cooked rice quality attributes (water uptake ratio, volume expansion ratio, hardness, and springiness). These results suggest that order changes of high- and low-temperature conditions can affect the intermediate quality of the stored rice but have limited influence on the final quality.