Effects of oligosaccharides on particle structure, pasting and thermal properties of wheat starch granules under different freezing temperatures

Insights into the correlations between the size of starch at nano- to microscale and its functional properties based on asymmetrical flow field-flow fractionation

In this study, the starches were isolated from three botanical sources (i.e., rice, sweet potato, and lotus seed). The size distributions of starch granules and molecules were determined by asymmetrical flow field-flow fractionation (AF4), and compared with those measured from optical microscopy (OM) and dynamic light scattering (DLS). Furthermore, the starches were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). AF4 coupled online with UV-visible, multiangle light scattering (MALS), and differential refractive index (dRI) detectors (AF4-UV-MALS-dRI) was employed for the investigation of the digestion and retrogradation properties of starches. Meanwhile, the relationships between the size of starch at nano- to microscale and its functional properties (i.e., digestibility, retrogradation, and thermal properties) were studied by Pearson correlation analysis. AF4-UV-MALS-dRI was proved to be a rapid and gentle method for the separation and size characterization of starches at both micro- and nano-molecule levels. Moreover, it was demonstrated that AF4-UV-MALS-dRI is a useful tool for the monitoring of the digestion and retrogradation properties of starches. The results suggested that the sizes of starch granules and molecules were to some extent correlated with their thermal properties and digestibility, but not with retrogradation property.

[Development of an asymmetrical flow field-flow fractionation system for the size characterization of starch granules]

淀粉颗粒粒径与分子尺寸分别在1~100 μm和20~250 nm之间,是影响淀粉功能特性的重要因素之一。非对称场流分离(AF4)是一种基于样品与外力场相互作用机制的分离技术,已应用于表征淀粉分子尺寸分布。商品化的AF4系统的粒径检测范围为1 nm~10 μm,对于淀粉颗粒粒径表征具有一定的局限性。该文研制了AF4分离系统;考察了其在微米尺度下对红薯、莲子和大米淀粉颗粒粒径表征的性能;采用微米尺寸的聚苯乙烯乳化球(PS)标准样品验证了构建的AF4系统的分离性能。实验结果显示,构建的AF4系统对PS混合样品(粒径2、6、12、20 μm)实现了基线分离,同商品化AF4相比提高了检测上线,具有分离表征淀粉颗粒的潜力。此外,该文研究了载液组成对淀粉颗粒分离表征的影响;通过光学显微镜验证了构建的AF4系统在微米尺度上对淀粉颗粒粒径分布的表征能力。最后,采用商品化的AF4系统串联多角度激光光散射检测器和示差折光检测器对3种淀粉分子进行了分离表征,考察了淀粉的溶解温度对其表征结果的影响。在摩尔质量10 ⁶~10⁸ g/mol范围内,红薯和莲子淀粉的回转半径和水合半径的比值(R_g/R_h)在0.9~1.1之间,大米淀粉的R_g/R_h在1.2~1.4之间。实验结果证明构建的AF4系统是一种快速、准确的淀粉颗粒粒径表征方法,与商品化的AF4系统结合可为研究淀粉尺寸分布与其功能性质之间的关系提供技术支持。

Effect of hydrocolloids on physical, thermal and microstructure properties of par-baked baguette during frozen storage

The retrogradation of starch occurs in the process of freezing storage of par-baked baguette, resulting in easy staling and a decrease of consumer acceptance. The objective of this study was to assess whether the staling of par-baked baguette could be improved by the addition of Arabic gum (AG), Sodium alginate (SA), and Sesbania gum (SG). The physical, thermal dynamic, and microstructure properties of par-baked baguette during frozen storage were analyzed. The addition of hydrocolloid increased the moisture of the baguette and delayed the water migration, which was beneficial to improve the dough formation and gas capacity, hinder the growth of ice crystals, and reduce the hardness of the baguette. These properties were more pronounced with increasing freezing storage periods. These hydrocolloids could slow down the rate of recrystallization, which reduced the enthalpy change and crystallinity of par-baked baguette. It was also found that the hydrocolloids incorporated baguette was smooth in the crumb microstructure. In general, these results suggested that the incorporation of hydrocolloids improved the quality and anti-staling mechanism of the par-baked baguette during frozen storage which can be used as potential improvers to increase freezing stability in the formulation of the baguette.