Granular size of potato starch affects structural properties, octenylsuccinic anhydride modification and flowability

• The physicochemical properties of large-, medium- and small-size potato starch fractions were investigated.
• The relative reactivity and OS group distribution of three size fractions were studied.
• Smaller granular size increases flowability so does OSA modification.

Native potato starch (PS) granules were separated into three size fractions: larger than 30 μm (P-L), 15–30 μm (P-M), and smaller than 15 μm (P-S). The morphological and crystalline structure of fractionated potato starches were investigated by light and scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The P-L fraction showed ellipsoidal shape and B-type X-ray pattern, whereas the P-S fraction had spherical shape and A-type pattern. The fluorophore-assisted capillary electrophoresis data showed that the P-L fraction had more B2 chains and less short A and B1 chains than the P-S counterparts. Smaller granules with larger specific surface area had higher degree of substitution when reacted with octenylsuccinic anhydride (OSA), and showed more uniform distribution of octenylsuccinate substituents. Both OSA modified and unmodified P-S samples showed higher flowability compared with the P-L counterparts.