Abstract
Abstract: Starch is one of the most abundant renewable biological resources and the primary source of stored energy in most plants. But native starch possesses many limitations such as low water solubility, thermal decomposition and chemical activity and high tendency towards retrogradation, which to some extent restricts its processing and application. Rolling technology is an effective physical modification means. It is simple, safe and has no pollution. In addition, it has significant impact on properties and structure of starch, which has a significant and great prospect in future. In this paper, a variety of advanced instrumental analysis techniques were used, which included scanning electron microscope (SEM), polarizing microscope (PLM), confocal laser scanning microscopy (CLSM), X-ray diffraction (XRD), differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and Rapid Visco Analyzer (RVA). Normal corn starches processed by different rolling time and speeds were investigated to demonstrate the effect of rolling on structure and physicochemical properties of corn starch. Structures of normal corn starch such as granular structure, channel structure, particle size distribution, crystalline structure and functional group were analyzed. The properties of starch, including water soluble index, swelling power, transparency, paste stability of corn starch, were studied. And pasting properties and thermal characteristics were comparatively analyzed. Under the frequency of 20 Hz, the results showed that when grinding mill processed for 3-6 h, the particle size of granule underwent a corresponding change with the morphological structure of corn starch changing erratically. The central cavity became larger and the channel was blurred. The DSC results indicated the gelatinization temperatures of the starches were not significantly altered by rolling, but the gelatinization enthalpies were significantly reduced in line with the reduction in the amount of double helices. At the same time, there was no significant decline in the degree of crystallinity. The results showed that the double helices content decreased after rolling treatment but the crystalline structure was seldom destroyed. In other word, rolling treatment had merely impact on double helix structure of amorphous region of corn starch granule. With the increasing of processing time, some bulbous protuberances were formed on the granule surface. And the water solution index, welling power, and transparency presented a significant decrease. Furthermore, peak viscosity and enthalpy of the corn starch also decreased gradually with the rolling time increasing. And crystalline regions still experienced a little damage. It was supposed that aggregation occurred in crystalline regions, which resulted in the formation of bulbous protuberance and the change of properties of corn starch. As the rolling processing time increased to 12 h, the SEM and CLSM analysis revealed that bulbous protuberances of particle surface became less obvious, some debris attached to large particles and the number of channels was increased. Particle size of granules was found to increase but opposite trend was found in enthalpy. Meanwhile, the feature of diffraction peaks observed in the diffractogram was gradually weakened, and crystal structure was severely damaged. At this stage, rolling destroyed the crystalline area of corn starch granules in accompany with the double helical content decreasing. Under the frequency of 30 Hz, due to the shear force is stronger, the effect of rolling treatment on structure and properties of normal corn starch was more obvious. The FTIR analysis showed that rolling treatment significantly decreased the absorption peak intensity at the band of 1 047 cm?1 corresponding to the amorphous part of starch structure, which confirmed the results of enthalpy. In conclusion, the above results demonstrate that rolling treatment has different mechanochemical effect on the amorphous and crystalline regions of corn starch granule, and leads to typical aggregation and agglomeration effects occurring successively in the interior of the starch granules. This study offers significant evidences for further investigations on the mechanochemical theory. What is more, it provides a convenient, rapid, efficient and green new modification technology for starch deep processing.
DownLoad: