Gelatinization and Pasting Property of Small Granular Starch from Chlamydomonas reinhardtii and Its Structural Basis

The gelatinization and pasting behavior of starch play a critical role in governing its suitability for various food and non-food applications. Although <i>Chlamydomonas reinhardtii</i> is the most-studied microalga, its starch gelatinization and pasting properties have remained elusive. In this study, we applied nitrogen limitation to promote the starch accumulation of <i>C. reinhardtii</i> and recovered the starch using high-pressure homogenization. The multiscale structure and properties of <i>C. reinhardtii</i> starch (CRS) were comprehensively analyzed and compared with those of commonly used terrestrial plant starch. Results showed that CRS possesses a unique multiscale structure characterized by an exceptionally high degree of branching (18.6%) and a thinner crystalline lamellae (9.29 nm). While maintaining an A-type crystalline pattern, CRS granules exhibited higher crystallinity compared with other microalgal starches. CRS had an irregular red blood cell-like morphology with a small size (~1 μm diameter). Physicochemical analysis revealed that CRS has an intermediate gelatinization temperature and a pasting profile defined by low viscosity and remarkable shear resistance, suggesting high stability during hydrothermal processing. Significantly, cooked CRS demonstrated a lower hydrolysis rate and higher resistant starch content than several common terrestrial starches. It is attributed to its higher degree of branching and superior thermostability. This study extends the fundamental knowledge of CRS and provides a critical scientific basis for its application as a novel, sustainable ingredient with special gel properties in the future food industry.