Investigating the crystalline structure and structural heterogeneity of starch granules using polarization-based...

A thorough understanding of starch structure from crystal distribution level is crucial for production, processing, and application of starch. In this study, we utilized a custom-built polarization-based quantitative phase microscopy based on digital holography as well as a multimodal polarization microscope to investigate the crystalline structure of starch granules at the level of the Maltese cross. Through quantitative analysis, we observed that crystalline regions are distributed on both sides of the granules, with non-crystalline material extending radially in between, with amylose playing a significant role in disrupting this crystal alignment. This offers insights into why starch granules exhibit low overall crystallinity, often below 20%, as observed in maize and potato starches. Additionally, in situ enzymatic hydrolysis and digestion analysis of starch granules revealed the rapid breakdown of granular structures at specific points in the process. The crystalline heterogeneity, quantified as variation in birefringence intensity (with standard deviations of 25-50% for maize starch and 13-25% for potato starch), which was observed across the granule population of the same starch type, resulted in asynchronous granule disruption, emphasizing the structural complexity within starch granules. These findings contribute to a deeper understanding of current models of starch structure, particularly in terms of how crystalline and amorphous regions interact during gelatinization and enzymatic processes. This study offers deeper insights into starch structure-function relationships and underscores the value of digital holographic quantitative phase microscopy for starch analysis.