To begin with, what is aged rice and new rice? Aged rice or old rice is nothing but stocked rice which is kept for ageing for one or more years. On the other hand, new rice is the one which is produced from newly harvested crops. Compared to the fresh aroma of new rice, aged rice is light and tasteless, which is essentially a change in the internal microscopic morphological structure of aged rice.
Researchers analyzed new rice and aged rice using the CIQTEK tungsten filament scanning electron microscope SEM3100. Let's see how they differ in the microscopic world!
CIQTEK Tungsten Filament Scanning Electron Microscope SEM3100
Figure 1 Cross-sectional fracture morphology of new rice and aged rice
First, the microstructure of rice endosperm was observed by SEM3100. From Figure 1, it can be seen that the endosperm cells of new rice were long polygonal prismatic cells with starch grains wrapped in them, and the endosperm cells were arranged in a radial fan shape with the center of the endosperm as concentric circles, and the endosperm cells in the center were smaller compared with the outer cells. The radial fan-shaped endosperm structure of new rice was more obvious than that of aged rice.
Figure 2 Microstructure morphology of the central endosperm of new rice and aged rice
Further magnified observation of the central endosperm tissue of rice revealed that the endosperm cells in the central part of aged rice were more broken and the starch granules were more exposed, making the endosperm cells radially arranged in a blurred form.
Figure 3 Microstructure morphology of protein film on the surface of new rice and aged rice
The protein film on the surface of the endosperm cells was observed at high magnification using the advantages of SEM3100 with high-resolution imaging. As can be seen from Figure 3, a protein film could be clearly observed on the surface of new rice, while the protein film on the surface of aged rice was broken and had different degrees of warping, resulting in relatively clear exposure of the internal starch granule shape due to the reduction of the surface protein film thickness.
Figure 4 Microstructure of endosperm starch granules of new rice
Rice endosperm cells contain single and compound amyloplasts. Single-grain amyloplasts are crystalline polyhedra, often in the form of single grains with blunt angles and obvious gaps with the surrounding amyloplasts, containing mainly crystalline and amorphous regions formed by straight-chain and branched-chain amylose [1,2]. The complex grain amyloplasts are clearly angular in shape, densely arranged, and tightly bound to the surrounding amyloplasts. Studies have shown that the starch grains of high-quality rice exist mainly as complex grains [3]. By observing the endosperm cells of new rice, as shown in Figure 4, the starch grains mostly existed in the form of compound grains. The compound starch grains were clearly angular in shape and closely bound to the surrounding starch grains, showing the endosperm structure of high-quality rice.
Rice quality is prone to change during storage. As the storage time increases, the hardness of rice increases, the viscosity and elasticity decrease, and the taste deteriorates, and these quality changes are closely related to morphological and structural characteristics such as the shape and arrangement of endosperm cells [4].
The microstructure of a material determines its various properties, and it is these differences in microstructure that make the rice we eat every day exhibit different taste values. Scanning electron microscopy, as a microscopic analysis tool, not only allows various forms of observation of food materials, but also provides a reliable basis for food research, and plays an important role in food safety testing and quality improvement.
References.
[1] Mohapatra D, Bal S. Cooking quality and instrumental textural attributes of cooked rice for different milling fractions [J]. Journal of Food Engineering, 2006, 73(3):253-259.
[2] Zhou Xianqing, Zhang Yurong, Li Rit. Microstructural changes of japonica rice endosperm under different simulated storage conditions[J]. Journal of Agricultural Engineering, 2010(5):6.
[3] Fu Wenying, Xiang Yuanhong. Microstructure of endosperm of edible high-quality rice[J]. Journal of Hunan Agricultural University: Natural Science Edition, 1997, 23(5):8.
[4] Xu M, Cheng W D, Cai X H, et al. Effect of storage on starch structure and content of rice[J]. Chinese Agronomy Bulletin, 2005, 21(6):113-113.
