The development of sustainable, nutrient-dense food systems requires a comprehensive understanding of how microalgae influence the mechanical properties of starch hydrogels. While certain microalgae are common food additives, a critical research gap remains regarding their effect on the rheological behavior and structural integrity of potato starch gels specifically. This study addressed this gap by evaluating the mechanical, microstructural and optical impacts of
Arthrospira platensis (commonly known as Spirulina) and
Chlorella vulgaris at 0.5%, 1% and 2% (
w/
w). Utilizing steady-shear flow tests, colorimetry, NIR spectroscopy and microscopy, we characterized changes in steady rheological parameters, color, chemical changes and microstructure of fortified hydrogels. Results indicated that filamentous
Arthrospira platensis reinforces the matrix, significantly increasing yield stress from 10.2 Pa in the control to 32.4 Pa at 2% inclusion. In contrast, spherical
Chlorella vulgaris appears to act as a structural filler, reducing yield stress to 4.8 Pa at 2%. Microscopy confirmed these morphological influences, showing
Arthrospira platensis filaments entangling granules while
Chlorella cells integrated into inter-granular spaces. Colorimetry revealed significant darkening (
L* decreased from 31.59 to 18.54 at 2%
Spirulina addition) and significant greening (
p < 0.05). NIR spectroscopy demonstrated potential physical interactions via vibrational markers at 5172 cm
−1 and 5646 cm
−1, indicating water matrix redistribution within the system. This research demonstrates how incorporating
Spirulina and
Chlorella vulgaris provides a viable approach for modifying the physical properties of starch-based matrices. The findings indicate that
Spirulina enhances flow resistance and structural stability under steady shear, whereas
Chlorella vulgaris reduces flow barriers, thereby increasing the spreadability of these composite food systems.
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