Impact of granule size on microstructural changes and oil absorption of potato starch during frying

Abstract

Potato starch (PS) was divided into three fractions: small granules (PS-S), medium granules (PS-M), and large granules (PS-L) using a gravity sedimentation method. The chemical composition, particle size distribution, and physicochemical properties of these three starch fractions were measured. The amylose content was proportional to granule size, increasing from 20.3% in PS-S to 27.3% in PS-L. As the granule size increased, the lipid, protein, and phosphorous contents of the starch granules decreased. The swelling power and water-solubility of the starch granules also decreased with increase in granule size. Each fraction was fried either at low (25%) or high (50%) moisture conditions. The hierarchical structural changes of the fried samples were further characterized using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and size exclusion chromatography. The effect of starch granule dimensions on oil absorption was evaluated using low-field nuclear magnetic resonance (LF-NMR). During frying, the granular morphology gradually disappeared, the crystalline structures destroyed, the crystalline lamellae collapsed, and the starch molecules degraded, which impacted the oil absorption behavior of the fried samples. Under low moisture conditions (25%), the granular state was preserved after frying, indicating that the size and porosity of the granules played a dominant role in the oil absorption process, explaining why PS-S absorbed the highest level of oil (0.166 g/g). Conversely, under high moisture conditions (50%), PS-L absorbed the highest level of oil (0.349 g/g) because it had a loose structure with the lowest crystallinity (4.2%), mass fractal index (Dm = 1.38), and molecular density index (ρ = 7.47 g/mol/nm3). The enhanced understanding of the relationship between starch particle size and oil absorption obtained through this research will facilitate the development of healthier fried foods with lower oil contents.