Short-chain glucan aggregate (SCGA) is a starch nanoparticle formed by self-assembly of short-chain glucans (SCGs) obtained through enzymatic debranching of starch. It is a submicron-sized particle that functions as a type of resistant starch and exhibits notable inhibitory effects on α-amylase activity. Therefore, SCGA has been studied as a promising material due to its potential to attenuate glycemic response. Hydroxypropylation (HP) is a chemical modification method that hydroxypropyl groups replace the hydroxyl groups of starch, thereby delaying starch retrogradation and increasing paste transparency. HP increases resistant starch content and enhances water retention, consequently inhibiting amylase activity. However, there have been no reports on the properties of hydroxypropylated SCGA (HPSC). Thus, this study aimed to investigate the physicochemical properties of hydroxypropylated SCGA.

SCGA was produced by gelatinizing waxy corn starch, debranching it with pullulanase, and self-assembling the resulting SCG. HP was carried out by inducing an ether bond with 0 (HPSC0), 12% (HPSC12), and 24% (HPSC24) propylene oxide at pH 11.5. The degree of substitution (DS), DSC, XRD, NMR, SEM, in-vitro digestibility, and α-amylase inhibition of the samples were analyzed.

Native SCGA (NSC) and HPSC0 showed no DS, whereas HPSC12 and HPSC24 revealed DS values of 0.048 and 0.092, respectively. Annealing treatment under alkaline conditions during hydroxypropylation prevented agglomeration of SCGA particles. Moreover, the structural rearrangement induced by annealing resulted in the highest enthalpy and relative crystallinity in HPSC0. However, in HPSC24, the DS was sufficiently high to offset the effects of annealing, leading to decreases in both enthalpy and relative crystallinity. These results suggest that the introduced hydroxypropyl groups in HPSC24 interfered with double-helix formation and reduced the development of crystalline structures. Water retention capacity decreased in HPSC0 because alkaline treatment formed particles with a more ordered structure, but it showed an increase after hydroxypropylation. For in-vitro digestibility, all HPSC samples exhibited higher RS contents than NSC. HPSC0 showed the highest RS content, indicating that the structural reorganization caused by annealing most effectively hindered enzymatic digestion. According to a previous study, SCGA was reported to act as a competitive-type inhibitor of α-amylase. HPSC24 demonstrated the strongest α-amylase inhibitory effect, possibly due to their loosened double-helical structures leading to not only compete with the substrate but also entrap α-amylase. Overall, hydroxypropylated SCGA could enhance RS content and inhibit α-amylase activity, due to alkaline annealing and their looser structure formed by hydroxypropyl substitution, respectively. Hydroxypropylated SCGA have potential as a material capable of lowering postprandial glycemic response and can be utilized as a promising carrier for other bioactive compounds.